Chapter V: I D C L L L I M I I V (3)

Baltimore and Ohio Railroad Company. _A list of the officers and employees of the Baltimore and Ohio Railroad for November, 1857._ Baltimore, 1857.

----. _Third annual report of the president and directors to the stockholders of the Baltimore and Ohio Rail Road Company._ Baltimore: 1829. (Also the fourth through 38th annual reports. Baltimore, 1830-1864.)

----. _Baltimore and Ohio exhibits at the Century of Progress._ Chicago, 1934.

_Biographical cyclopedia of representative men of Maryland and the District of Columbia._ Baltimore, 1879.

BOLLMAN, WENDEL. _Iron suspension and trussed bridge as constructed for the Baltimore and Ohio Rail Road Co. at Harper's Ferry, and on the Washington branch of this road._ Baltimore, 1852.

----. Letter to John W. Garrett dated June 17, 1862. In files of Division of Mechanical and Civil Engineering, United States National Museum, Washington, D.C.

----. _Report of Mr. Bollman in relation to Central Ohio Rail Road._ Baltimore, 1854.

BRYANT, WILLIAM C. _Picturesque America._ New York, 1874.

CLARKE, THOMAS CURTIS. _An account of the iron railway bridge across the Mississippi River at Quincy, Illinois._ New York, 1869.

COLBURN, ZERAH. American iron bridges. _Minutes of the proceedings of the Institution of Mechanical Engineers_ (1863), vol. 22, pp. 540-573.

CONDIT, CARL. _American building art:--The nineteenth century._ New York: Oxford Press, 1960.

GRAY, GEORGE E. Notes on early practice in bridge building. _Transactions of the American Society of Civil Engineers_ (1897), vol. 37, pp. 2-16.

GREINER, JOHN E. The American railroad viaduct--Its origin and evolution. _Transactions of the American Society of Civil Engineers_ (1891), vol. 25, pp. 349-372.

LANG, PHILIP GEORGE. Bollman trusses on Valley of Virginia Branch will soon be memories. _Baltimore and Ohio Magazine_ (October 1923), pp. 18-19.

----. The old Baltimore and Ohio bridge crossing the Potomac River at Harpers Ferry, West [sic] Virginia. _Engineering News-Record_ (September 17, 1931), p. 446.

MALEZIEUX, EMILE. _Travaux publics des Etats-Unis d'Amerique en 1870._ Paris, 1873.

MCDOWELL, W. H. Unpublished engineer's report to the president and directors of Wilmington Railway Bridge Company, Wilmington, North Carolina, dated March 12, 1868. Typewritten copy in files of Division of Mechanical and Civil Engineering, U.S. National Museum, Washington, D.C.

SMITH, CHARLES SHALER. _Comparative analysis of the Fink, Murphy, Bollman and triangular trusses._ Baltimore, 1865.

SMITH, WILLIAM P. _The book of the great railway celebrations of 1857._ Baltimore, 1858.

TYRRELL, HENRY G. _History of bridge engineering._ Chicago, 1911.

WHIPPLE, SQUIRE. _Bridge building._ Albany, New York, 1869.

* * * * *

CONTRIBUTIONS FROM
THE MUSEUM OF HISTORY AND TECHNOLOGY:

PAPER 37

SCREW-THREAD CUTTING BY THE MASTER-SCREW METHOD SINCE 1480

_Edwin A. Battison_

_Edwin A. Battison_

SCREW-THREAD CUTTING BY THE MASTER-SCREW METHOD SINCE 1480

_Among the earliest known examples of screw-thread cutting machines
are the screw-cutting lathe of 1483, known only in pictures and
drawings, and an instrument of the traverse-spindle variety for
threading metal, now in the Smithsonian Institution, dating from the
late 17th or early 18th century. The author shows clearly their
evolution from something quite specialized to the present-day tool.
He has traced the patents for these instruments through the early
1930's and from this research we see the part played by such devices
in the development of the machine-tool industry._

THE AUTHOR: _Edwin A. Battison is associate curator of mechanical
and civil engineering in the Smithsonian Institution's Museum of
History and Technology._

Directness and simplicity characterize pioneer machine tools because they were intended to accomplish some quite specialized task and the need for versatility was not apparent. History does not reveal the earliest forms of any primitive machines nor does it reveal much about the various early stages in evolution toward more complex types. At best we have discovered and dated certain developments as existing in particular areas. Whether these forms were new at the time they were first found or how widely dispersed such forms may have been is unknown. Surviving evidence is in the form of pictures or drawings, such as the little-known screw-cutting lathe of 1483 (fig. 1) shown in _Das mittelalterliche Hausbuch_.

This lathe shows that its builder had a keen perception of the necessary elements, reduced to bare essentials, required to accomplish the object. Present are the coordinate slides often credited to Henry Maudslay. His slides are not, of course, associated with the spindle; neither is there any natural law which compels them to guide the tool exactly parallel with the axis of revolution. In this sense the screw-cutting lathe in the _Hausbuch_ is superior because it is in harmony with natural law and can generate a true cylinder, whereas Maudslay's lathe can only transfer to the work whatever accuracy is built into it.

In principle this machine shown in the _Hausbuch_ is very advanced as we see when we follow the design through to the present time. The artist, whose drawings give us our only knowledge of the machine, himself was obviously not very familiar with the details of its function. Reference to figure 1 shows that the threads on the lead screw and on the work, wind in opposite directions. This must be an error in delineation since the two are closely coupled together without any intervening mechanism so that the only possible result on the work must be a thread winding in the same direction as on the original screw. The work also is shown threaded for its entire length; this cannot be accomplished with any one location of the cross-slide. We are left with the question of whether this slide was used in two locations or whether the artist, possibly working from notes or an earlier rough sketch, failed to show an unthreaded portion on one end or the other of the work.

Of at least equal importance with the lead screw and work and their relationship to each other is the tool-support with its screw-adjusted cross-slide (fig. 2). Just how this was attached to the frame of the machine so that it placed the tool at a suitable radius is again a questionable point. The very well-developed cutting tool is sharpened to a thin, keen edge totally unsuited for cutting metal but ideal for use on a softer, fibrous substance: undoubtedly wood, in this instance. Unfortunately, the angle at which the artist chose to show us this cutter is not a view from which it is possible to judge whether or not the tool has been made to conform to the helix angle of the thread to be cut. This cross-slide, in conjunction with the traversing work spindle, gives us a machine having two coordinate slides yielding the same effect as the slide rest usually attributed to Henry Maudslay at the end of the 18th century. Actually, an illustration of coordinate slides independent of the spindle had been published as early as 1569 by Besson[1] and knowledge of them widely disseminated by his popular work on mechanics. These slides are shown as part of a screw-cutting machine with a questionably adequate connection, by means of cords, between the master screw and the work.

It was the author's pleasure recently to obtain for the Smithsonian Institution and identify a small, nicely made, brass instrument which had been in two collections in this country and one collection in Germany as an unidentified locksmith's tool (fig. 3). This proved to be an instrument of the traverse-spindle variety for threading metal. Fortunately, all essential details were present including a cutter (A in figure 4); this instrument was identified by the signature "Manuel Wetschgi, Augspurg." The Wetschgis were a well-known family of gunsmiths and mechanics in Augsburg through several generations. Two bore the given name Emanuel: the earlier was born in 1678 and died in 1728. He was quite celebrated in his field of rifle making and became chief of artillery to the Landgrave of Hesse-Kassel shortly before his death in his 51st year. Little is known of the later Emanuel Wetschgi except that he was at Augsburg in 1740. Tentative attribution of the instrument has been made to the earlier Emanuel, chiefly on the basis of his recognized position as an outstanding craftsman.

In several respects this little machine differs from its predecessor of the _Hausbuch_, as might be expected when allowance is made for the generations of craftsmen who undoubtedly worked with such tools over the roughly 200 years of time separating them. Another factor to consider when comparing these two machines is that one was used on metal, the other probably only on wood. Therefore, it is not surprising to find on the later machine an outboard or "tailstock" support for the work. The spindle of this support has to travel in unison with the work-driving spindle so that it is not an unexpected discovery to find that it is spring-loaded. Figure 5 shows how this spring may be adjusted to accommodate various lengths of work by moving the attachment screw to various holes in both the spring and in the frame. Also visible in the same illustration is a rectangular projection at the other end of the spring which engages a mating hole in the "tailstock" spindle to prevent its rotation.

Figure 6 shows the traversing spindle and nut removed from the machine. Provision has been made for doing this so easily that there is every reason to believe that, originally, there were various different spindle and nut units which could be interchangeably used in the machine. Additional evidence tending to support this concept exists in the cutting tool (fig. 4), which must have been intended for serious work as it has been carefully fitted in its unsymmetrical socket. The cutting blade of this tool, which works with a scraping rather than a true cutting action, is too wide to form a properly proportioned thread when used with the existing lead screw. This may well indicate that the tool was made for use with a lead of coarser pitch, now lost.

Perhaps the most startling feature of this machine when compared with the machine of the _Hausbuch_, is the absence of a cross-slide for adjusting the tool. Possibly this can be explained by the blunt scraping edge on the tool. In actual use, recently, to cut a sample screw, using a tool similar to the one found in the machine (fig. 7), it was found advantageous to be free of a cross-slide and thus be able to feed the tool into the work by feel rather than by rule, as would be done with a slide rest. In this way, it was possible to thread steel without tearing, as the cutting pressure could readily be felt and the tool could release itself from too heavy a cut. Size on several screws could be repeated by setting the tool to produce the desired diameter when its supporting arm came to rest against the frame of the machine. The screws used in the machine itself were apparently made in just such a way. They were not cut with a die as the thread blends very gradually into the body of the screw without the characteristic marks left by the cutting edges of a die. Threads cut with a single-point tool controlled by a cross-slide usually end even more abruptly than those cut by a die, while it would be quite simple with a machine of the nature we are considering to bring the thread to a gentle tapering end as seen in figure 8 (another view of the screw A in fig. 3) by gradually releasing the pressure necessary to keep the tool cutting as the end of the thread was approached.

That machines of this general type having the lead screw on the axis of the work were competitive with other methods and other types of machines over a long period of time may be seen from figures 9 and 10. The machine, left front in figure 9 and in more intimate detail in figure 10, can be seen to differ little from that shown in _Das mittelalterliche Hausbuch_ of 1483. The double work-support is, of course, a great improvement, while the tool-support is regressive since it lacks a feed screw.

The development of engineering theory, coupled with the rising needs of industry, particularly with the advent of the Industrial Revolution, brought about accelerated development of screw-cutting lathes through the combination of screw-cutting machines with simple lathes as seen in figure 9 and in detail in figure 11. One important advance shown here is driving the machine by means of a cord or band so that any means of rotary power could be applied, not just hand or foot power. Of greater interest and technical importance to this study is the provision, seen to better advantage in figure 11, for readily changing from one master lead screw to another. This had already been achieved in the Manuel Wetschgi machine, as far as versatility is concerned, although not in quite such a convenient way.

Figure 12, the headstock of another and more advanced lathe than shown in figures 9 and 11 but of the same type, shows "keys" (D), each of which is a partial nut of different pitch to engage with a thread of mating pitch. The dotted lines in figure 13 show the engaged and disengaged positions of one of these keys, and figure 14 shows the spindle with the various leads, C. At D is a grooved collar to be engaged by the narrow key shown in operating position at the left in figure 12 for the purpose of controlling the endwise movement of the spindle when used for ordinary turning instead of thread-cutting. In return for greater convenience and freedom from the expense of the many separate spindles, as typified by the Wetschgi machine, a sacrifice has been made in the length of the thread which can be cut without interruption.

This reduction in the length that could conveniently be threaded was no great drawback on many classes of work. This can be realized from figure 16 which shows a traverse-spindle lathe headstock typical of the mid-19th century. During the years intervening between the machines of figures 12 and 16, the general design was greatly improved by removing the lead screws from the center of the spindle. This made possible a shorter, much stiffer spindle and supported both ends of the spindle in one frame or headstock rather than in separate pieces attached to the bed. The screws were now mounted outside of the spindle-bearings, one at a time, while the mating nuts were cut partially into the circumference of a disk which could be turned to bring any particular nut into working position as required. With this arrangement, a wide variety of leads either right or left hand could be provided and additional leads could be fitted at any future time. Screw-cutting lathes of this design were popular for a very long time with instrument makers and opticians who had little need to cut screws of great length.

The demands of expanding industry for greater versatility in the production of engineering elements late in the 18th century set the stage for the evolution of more complex machines tending to place the threaded spindle lathes in eclipse. Maudslay's lathe of 1797-1800 (fig. 15) appeared at this time when industry was receptive to rapid innovation. Unfortunately, the gearing which once existed to connect the headstock spindle with the lead screw has long been lost. At this time it is quite difficult to say with certainty whether the original gear set offered a variety of ratios, as was true of slightly later Maudslay lathes, or a fixed ratio. The plausibility of the fixed ratio theory is supported by the very convenient means, seen in figure 15, for removing the lead screw in preparation for substitution of one of another pitch. All that is required is to back off its supporting center at the tailstock end and withdraw the screw from its split nut[2] and from the driving clutch near the headstock. This split nut also would have to be changed to one of a pitch corresponding to that of the screw. While more expensive than a solid nut, it neatly circumvents the need (and saves the time involved) to reverse the screw in order to get the tool back to the point of beginning preliminary to taking another cut. David Wilkinson's lathe of 1798 (fig. 17) which was developed in Rhode Island at the same time shows the same method of mounting and driving the master screw. At least in the United States, this method of changing the lead screw instead of using change gears remained popular for many years. Examples of this changeable screw feature are to be found in the lathes constructed for the pump factory of W. & B. Douglas Company, Middletown, Connecticut,[3] in the 1830's. Middletown, at that time one of the leading metal-working centers in one of the chief industrial States, had been for many years the site of the Simeon North arms factory which rivaled Whitney's. In this atmosphere, it is reasonable to expect that machinery constructed by local mechanics, as was the custom in those days, would reflect the most accepted refinements in machine design.

Roughly twenty years later, Joseph Nason of New York patented[4] the commercially very important "Fox" brassworker's lathe (fig. 18). While this does have a ratio in the pair of gears connecting the work spindle and master screw, it is clear from the patent that various pitches are to be obtained by changing screws, not by changing gears. The patent sums it up as follows:

A nut upon the end of the stud ... is unscrewed when the guide
screw is to be removed or changed. The two wheels ... should have
in their number of teeth a common multiple. They are seldom or
never removed and their diameters are made dissimilar only for the
purpose of giving to the guide screw a slower rate of motion than
that of the mandrel whereby it may be made of coarser pitch than
that of the screw to be cut and its wear materially lessened.

The introduction of gearing between the spindle and the lead screw, for whatever purpose, could not help but introduce variable factors caused by inaccuracies in the gears themselves and in their mounting. These were of little consequence for common work, particularly when coupled to a screw which, itself, was of questionable accuracy. The increasing refinements demanded in scientific instruments and in machine tools themselves after they had reached a relatively stable form dictated that attention be dedicated to improved accuracy of the threaded components.

An attack on this problem, which interestingly reverts to the fundamental principle of motion derived from a master screw without the intervention of other mechanism (fig. 19), is covered by a patent[5] issued to Charles Vander Woerd, one-time superintendent of the Waltham Watch Company. The problem is well stated in the patent:

This invention relates to the manufacture of leading screws to be
used for purposes requiring the highest attainable degree of
correctness in the cutting of the screw-threads of said screw ...
as, for example, in machines for ruling lines in glass plates to
produce refraction [sic] gratings for the resolution of the lines
of the solar spectrum, such machines being required to rule many
thousands of lines on an inch of space by a marking device which is
reciprocated over the glass plate and is fed by the action of a
leading screw after the formation of each line. Great difficulty
has been experienced in constructing a leading screw for this and
other purposes, in which the thread is so nearly correct as to
produce no perceptible variation in the microscopic spaces between
the ruled lines or gratings.... Various causes prevent the
formation of a thread on the rod or blank, which is absolutely
uniform and accurate from end to end of the rod. Among other causes
are the variations of temperature from time to time, the
imperfections of the operating leading screw, the springing of the
leading screw and of the rod that is being threaded, and other
unavoidable causes, all of which, although apparently trivial and
producing only slight variations in the thread at different parts
of the rod or blank, are of sufficient moment to be seriously
considered when a screw of absolute accuracy is desired.

It is interesting to note in figure 19 that Vander Woerd's machine, to avoid the problems outlined in his patent, has returned to a starkly simple design. We are not told, however, how he originated this master screw which is used to produce the accurately threaded work pieces. Later generations, in the search for ever-greater accuracy, also returned to the fundamental simplicity of a master screw as we shall see when we consider the refinements in mechanism necessary to the extended development of the automobile and the airplane.

As the power and speed of automobiles and aircraft increased, critical parts became more highly stressed. Gears and threaded parts were particularly troublesome details of the mechanism because of the stresses concentrated in them, and, in the case of gears, because of the internal and external stresses originating in minute deviations from the ideal of tooth form and spacing. The problems were not entirely new but had hitherto been solved by increasing the size of the parts, an avenue of limited utility to designers in these fields where total weight as well as the effects of mass and inertia are so important. By making these parts of heat-treated steel, the strength could be made suitable while the size and mass of the parts were kept within bounds. The necessary processes of heat-treating were not always applicable to finished parts as they sometimes destroyed both finish and accuracy. Grinding, which was well developed for the simple plane, cylindrical, and conical surfaces so widely used in mechanisms, had to be extended to threads and gears so that they could be finished after heat-treating. Sometimes the gear teeth themselves were ground; for other applications it was sufficient to improve the accuracy of the gear cutters.

Attempts to produce gear hobs free of the imperfections and distortions introduced by heat treatment led to another return to the use of the master lead screw. Figure 20 illustrates a machine having this feature which was patented in 1932 by Carl G. Olson.[6] In speaking of the spindle-driving mechanism disclosed in earlier patents, the patent goes on to say:

This driving mechanism includes an integral spindle 20, one
extremity thereof being designed for supporting a hob 22 and the
other extremity thereof being formed so as to present a lead screw
24. The spindle 20 is mounted between a bearing 26 and a bearing
28, the latter bearing providing a nut in which the lead screw 24
rotates.... From the description thus far given it will be apparent
that the rotation of the lead screw 24 within the bearing or nut 28
will cause the hob to be moved axially, the lead of the screw 24
being equal to the lead of the thread in the hob.

Claim 8 which concludes the descriptive portion of the patent states in part:

In a hob grinding machine of the class described, a rotary work
supporting spindle, means for effecting longitudinal movement of
the spindle, a tool holder for supporting a grinding wheel in
operative position with respect to the work supported by the
spindle during the rotary and longitudinal movement thereof, ...

Even before this patent was applied for, another patent was pending for the purpose of modifying the pitch of the lead screw without the use of change gears in spite of the wide acceptance of such gear mechanisms for over a hundred years.

Figure 21 shows a plan view[7] of the machine, and figure 22 a detailed view of the sine-bar mechanism actuated by the master screw, 6, to modify the effective pitch of the lead screw in accordance with the realities of practice as stated in the preamble of the patent:

This invention relates to material working machines, and
particularly to machines such as hob grinders and the like, wherein
the work is reciprocated through the agency of a lead screw.

In the manufacture of hobs it is common practice to employ the same
machine for grinding hobs of varied diameters, and in order to
employ such a machine in this manner the pitch of the lead screw,
thereof, which actuates the work carrier, must conform to the axial
pitch of the hob to be ground. This will be readily apparent when
it is understood that the helix angles of hobs vary in accordance
with their diameters and, consequently, the difference between the
normal pitch and the axial pitch correspondingly varies. While the
requirement for the normal pitch may be the same for hobs of
different diameters, it is necessary to change the axial pitch in
accordance with a change in the hob diameter, and this axial pitch
of the hob is equal to the pitch of the lead screw which actuates
the work carrier in grinding machines heretofore used. Hence, in
order to adapt such machines to cover a wide range of leads, it is
necessary to provide a large number of interchangeable lead screws
and obviously this represents a large investment, and the
interchanging of these screws requires the expenditure of
considerable time in setting up the machine for each job.

Thread-grinding machines were being designed concurrent with the development of hob-grinding machines. Many were entirely concerned with features peculiar to the problems of wheel-dressing and to automatic characteristics. An invention to embody the use of a master screw and concerned with the precision grinding of worm threads, for use in gearing, was patented by Frederick A. Ward in this era.[8] That part of the invention pertaining to the use of a master screw, "a rotary work holder mounted on said carriage and provided with a driving spindle, an exchangeable master screw and stationary nut detachably secured to said spindle and head,..." is shown in figure 23.

Machines embodying the principle of the master lead screw are found in constant use by industry at the present time for specialized application. Whenever technological changes again reopen the topic of thread-cutting to a new degree of accuracy or call for a reevaluation of popular methods for any other reason, we may expect to see another resurgence of the master-screw method, for no other design eliminates so many variables or rests on such firm and fundamental natural principles as the machine of _Das mittelalterliche Hausbuch_ of 1483, the earliest such machine now known.

* * * * *

FOOTNOTES

[1] JACQUES BESSON, _Des instruments mathématiques, et méchaniques,
servants à l'intelligence de plusiers choses difficiles, &
necessaires à toutes républiques_, 1st ed. (Orleans, 1569).
[Also available in later editions in French, German, and
Spanish.]

[2] J. FOSTER PETREE, introduction, _Henry Maudslay, 1771-1831, and
Maudslay Sons and Field, Ltd._ (London: The Maudslay Society,
1949).

[3] _American Machinist_ (September 28, 1916), vol. 45, no. 13,
pp. 529-531.

[4] U.S. patent 10383 issued to Joseph Nason of New York, January 3,
1854.

[5] U.S. patent 293930 issued to Charles Vander Woerd of Waltham,
Massachusetts, February 19, 1884.

[6] U.S. patent 1874592, filed June 8, 1929, issued to C. G. Olson of
Chicago, Illinois, August 30, 1932, and assigned to the Illinois
Tool Works, also of Chicago.

[7] U.S. patent 1901926, filed February 16, 1928, issued to C. G.
Olson of Chicago, Illinois, March 21, 1933, and assigned to the
Illinois Tool Works, also of Chicago.

[8] U.S. patent 1899654, filed August 31, 1931, issued to F. A. Ward
of Detroit, Michigan, February 28, 1933, and assigned to the
Gear Grinding Company of Detroit, Michigan.

* * * * *

Typographical Corrections

Page 107: "... servants à l'intelligence de plusieurs choses difficiles,
& nécessaires ..." (had "a," "plusiers," "necessaires")

* * * * *

CONTRIBUTIONS FROM
THE MUSEUM OF HISTORY AND TECHNOLOGY:

PAPER 38

THE EARLIEST ELECTROMAGNETIC INSTRUMENTS

_Robert A. Chipman_

ELECTROSTATIC INSTRUMENTS BEFORE 1800 123

INSTRUMENTING VOLTAIC OR GALVANIC ELECTRICITY, 1800-1820 124

ELECTRICAL INSTRUMENTATION, 1800-1820 125

OERSTED'S DISCOVERY 126

BEGINNINGS OF ELECTROMAGNETIC INSTRUMENTATION 126

CHRONOLOGY AND PRIORITY 127

ORIGINAL ELECTROMAGNETIC MULTIPLIERS 129

CONCLUSIONS 135

ACKNOWLEDGMENTS 136

_Robert A. Chipman_

THE EARLIEST ELECTROMAGNETIC INSTRUMENTS

_The history of the early stages of electromagnetic instrumentation
is traced here through the men who devised the theories and
constructed the instruments._

_Despite the many uses made of voltaic cells after Volta's
announcement of his "pile" invention in 1800, two decades passed
before Oersted discovered the magnetic effects of a voltaic circuit.
As a result of this and within a five-month period, three men,
apparently independently, announced the invention of the "first"
electromagnetic instrument. This article details the merits of their
claims to priority._

THE AUTHOR: _Robert A. Chipman is chairman of the Department of
Electrical Engineering at the University of Toledo in Toledo, Ohio,
and consultant to the Smithsonian Institution._

Electrostatic Instruments before 1800

It is the fundamental premise of instrument-science that a device for detecting or measuring a physical quantity can be based on any phenomenon associated with that physical quantity. Although the instrumentation of electrostatics in the 18th century, for example, relied mainly on the phenomena of attraction and repulsion and the ubiquitous sparks and other luminosities of frictional electricity, even the physiological sensation of electric shock was exploited semiquantitatively by Henry Cavendish in his well-known anticipation of Ohm's researches. Likewise, Volta in 1800[1] described at length how the application of his pile to suitably placed electrodes on the eyelids, on the tongue, or in the ear, caused stimulation of the senses of sight, taste and hearing; on the other hand, he reported that electrodes in the nose merely produced a "more or less painful" pricking feeling, with no impression of smell. The discharges from the Leyden jars of some of the bigger frictional machines, such as van Marum's at Leyden, were found by 1785 to magnetize pieces of iron and to melt long pieces of metal wire.[2]

The useful instruments that emerged from all of this experience were various deflecting "electrometers" and "electroscopes" (the words were not carefully distinguished in use), including the important goldleaf electroscope ascribed to Abraham Bennet in 1787.[3]

In 1786, Galvani first observed the twitching of the legs of a dissected frog produced by discharges of a nearby electrostatic machine, thereby revealing still another "effect" of electricity. He then discovered that certain arrangements of metals in contact with the frog nerves produced the same twitching, implying something electrical in the frog-metal situation as a whole. Although Galvani and his nephew Aldini drew from these experiments erroneous conclusions involving "animal electricity," which were disputed by Volta in his metal-contact theory, it is significant from the instrumentation point of view that the frog's legs were unquestionably by far the most sensitive detector of metal-contact electrical effects available at the time. Without their intervention the development of this entire subject-area, including the creation of chemical cells, might have been delayed many years. Volta himself realized that the crucial test between his theory and that of Galvani required confirming the existence of metal-contact electricity by some electrical but nonphysiological detector. He performed this test successfully with an electroscope, using the "condensing" technique he had invented more than a decade earlier.

Instrumenting Voltaic or Galvanic Electricity, 1800-1820

In his famous letter of March 20, 1800, written in French from Como, Italy, to the president of the Royal Society in London, Volta made the first public announcement of both his "pile" (the first English translator used the word "column"), and his "crown of cups" (the same translator used "chain of cups" for Volta's "couronne de tasses"). The former consisted of a vertical pile of circular disks, in which the sequence copper-zinc-pasteboard, was repeated 10 or 20 or even as many as 60 times, the pasteboard being moistened with salt water. The "crown of cups" could be most conveniently made with drinking glasses, said Volta, with separated inch-square plates of copper and zinc in salt water in each glass, the copper sheet in one glass being joined by some intermediate conductor and soldered joints to the zinc in the next glass.

Volta considered the "crown of cups" and the "pile" to be essentially identical, and as evidences of the electrical nature of the latter, said:

... if it contains about 20 of these stories or couples of metal, it
will be capable not only of emitting signs of electricity by
Cavallo's electrometer, assisted by a condenser, beyond 10° or 15°,
and of charging this condenser by mere contact so as to make it emit
a spark, etc., but of giving to the fingers with which its
extremities (the bottom and top of the column) have been touched
several small shocks, more or less frequent, according as the
touching has been repeated. Each of these shocks has a perfect
resemblance to that slight shock experienced from a Leyden flask
weakly charged, or a battery still more weakly charged, or a torpedo
in an exceedingly languishing state, which imitates still better the
effects of my apparatus by the series of repeated shocks which it
can continually communicate.[4]

The "effects" provided by Volta's pile and crown-of-cups are therefore electroscope deflection, sparks, and shocks. Later in the letter, he describes the stimulation of sight, taste, and hearing as noted earlier, but nowhere does he mention chemical phenomena of any kind, or the heating of a wire joining the terminals of either device. Hence, except for the additional physiological responses, he adds nothing to the catalog of observations on which instruments might be based. His familiarity with the moods of the torpedo (electric eel) seems to be intimate.

The reading of Volta's letter to the Royal Society on June 26, 1800, its publication in the Society's _Philosophical Transactions_ (in French) immediately thereafter, and its publication in English in the _Philosophical Magazine_ for September 1800,[5] gave scientists throughout Europe an easily constructed and continuously operating electric generator with which innumerable new physical, chemical, and physiological experiments could be made. Editor-engineer William Nicholson read Volta's letter before its publication and, by the end of April, he and surgeon Anthony Carlisle had built a voltaic pile. Applying a drop of water to improve the "connection" of a wire lying on a metal plate, they happened to notice gas bubbles forming on the wire, and pursued the observation to the point of identifying the electrical decomposition of water into hydrogen and oxygen.

Within two or three years innumerable electrochemical reactions had been described, some of which, one might think, could have served as operating principles for electrical instruments. Although the phenomena of gas formation and metal deposition were in fact widely used as crude indicators of the polarity and relative strength of voltaic piles and chemical cells during the period 1800-1820 (and the gas bubbles were made the basis of a telegraph receiver by S. T. Soemmering), the quantitative laws of electrolysis were not worked out by Faraday until after 1830, and not until 1834 was he satisfied that the electrolytic decomposition of water was sufficiently well understood to be made the basis for a useful measuring instrument. Describing his water-electrolysis device in that year, he wrote:

The instrument offers the only _actual measurer_ [italics his] of
voltaic electricity which we at present possess. For without being
at all affected by variations in time or intensity, or alterations
in the current itself, of any kind, or from any cause, or even of
intermissions of actions, it takes note with accuracy of the
quantity of electricity which has passed through it, and reveals
that quantity by inspection; I have therefore named it a
VOLTAELECTROMETER.[6]

In passing, Faraday commented that the efforts by Gay-Lussac and Thenard to use chemical decomposition as a "measure of the electricity of the voltaic pile" in 1811 had been premature because the "principles and precautions" involved were not then known. He also noted that the details of _metal deposition_ in electrolysis were still not sufficiently understood to permit its use in an instrument.[7]

The heating of the wires in electric circuits must have been observed so early and so often with both electrostatic and voltaic apparatus, that no one has bothered to claim or trace priorities for this "effect." The production of incandescence, however, and the even more dramatic combustion or "explosion" of metal-foil strips and fine wires has a good deal of recorded history. Among the first to burn leaf metal with a voltaic pile was J. B. Tromsdorff of Erfurt who noted in 1801 the distinctly different colors of the flames produced by the various common metals. In the succeeding few years, Humphry Davy at the Royal Institution frequently, in his public lectures, showed wires glowing from electric current.

Early electrical instrumentation based on the heating effect took an unusual form. Shortly after 1800, W. H. Wollaston, an English M.D., learned a method for producing malleable platinum. He kept the process secret, and for several years enjoyed an extremely profitable monopoly in the sale of platinum crucibles, wire, and other objects. About 1810, he invented a technique for producing platinum wire as fine as a few millionths of an inch in diameter, that has since been known as "Wollaston wire." For several years preceding 1820, no other instrument could compare the "strengths" of two voltaic cells better than the test of the respective maximum lengths of this wire that they could heat to fusion. One can sympathize with Cumming's comment in 1821 about "the difficulty in soldering wires that are barely visible."[8]

Electrical Instrumentation, 1800-1820

The 20 years following the announcement of the voltaic-pile invention were years of intense experimental activity with this device. Many new chemical elements were discovered, beginnings were made on the electrochemical series of the elements, the electric arc and incandescent platinum wires suggested the possibilities of electric lighting, and various electrochemical observations gave promise of other practical applications such as metal-refining, electroplating, and quantity production of certain gases. Investigators were keenly aware that all of the available means for measuring and comparing the _electrical_ aspects of their experiments (however vaguely these "electrical aspects" may have been conceived), were slow, awkward, imprecise, and unreliable.

The atmosphere was such that prominent scientists everywhere were ready to pounce immediately on any reported discovery of a new electrical "effect," to explore its potentialities for instrumental purposes. Into this receptive environment came H. C. Oersted's announcement of the magnetic effects of a voltaic circuit, on July 21, 1820.[9]

Oersted's Discovery

Many writers have expressed surprise that with all the use made of voltaic cells after 1800, including the enormous cells that produced the electric arc and vaporized wires, no one for 20 years happened to see a deflection of any of the inevitable nearby compass needles, which were a basic component of the scientific apparatus kept by any experimenter at this time. Yet so it happened. The surprise is still greater when one realizes that many of the contemporary natural philosophers were firmly persuaded, even in the absence of positive evidence, that there _must_ be a connection between electricity and magnetism. Oersted himself held this latter opinion, and had been seeking electromagnetic relationships more or less deliberately for several years before he made his decisive observations.

His familiarity with the subject was such that he fully appreciated the immense importance of his discovery. This accounts for his employing a rather uncommon method of publication. Instead of submitting a letter to a scientific society or a report to the editor of a journal, he had privately printed a four-page pamphlet describing his results. This, he forwarded simultaneously to the learned societies and outstanding scientists all over Europe. Written in Latin, the paper was published in various journals in English, French, German, Italian and Danish during the next few weeks.[10]

In summary, he reported that a compass needle experienced deviations when placed near a wire connecting the terminals of a voltaic battery. He described fully how the direction and magnitude of the needle deflections varied with the relative position of the wire, and the polarity of the battery, and stated "From the preceding facts, we may likewise collect that this conflict performs circles...." Oersted's comment that the voltaic apparatus used should "be strong enough to heat a metallic wire red hot" does not excuse the 20-year delay of the discovery.

Beginnings of Electromagnetic Instrumentation

The mere locating of a compass needle above or below a suitably oriented portion of a voltaic circuit created an electrical instrument, the moment Oersted's "effect" became known, and it was to this basic juxtaposition that Ampère quickly gave the name of galvanometer.[11] It cannot be said that the scientists of the day agreed that this instrument detected or measured "electric current," however. Volta himself had referred to the "current" in his original circuits, and Ampère used the word freely and confidently in his electrodynamic researches of 1820-1822, but Oersted did not use it first and many of the German physicists who followed up his work avoided it for several years. As late as 1832, Faraday could make only the rather noncommittal statement: "By current I mean anything progressive, whether it be a fluid of electricity or vibrations or generally progressive forces."[12]

Nevertheless, whatever the words or concepts they used, experimenters agreed that Oersted's apparatus provided a method of monitoring the "strength" of a voltaic circuit and a means of comparing, for example, one voltaic battery or circuit with another.

It was perfectly clear, from Oersted's pamphlet, that if a compass needle was deflected clockwise when the wire of a particular voltaic circuit lay above it in the magnetic meridian, the same needle would _also_ be deflected clockwise if the wire was turned end-for-end and placed _below_ the compass needle, without changing the rest of the circuit. Anyone perceiving this fact might deduce, as a matter of logic, that if the wire of the circuit was first passed above the needle, in the magnetic meridian, then folded and returned in a parallel path below the needle, the deflecting effect on the needle would be repeated, and a more sensitive indicator would result, assuming that any additional wire introduced has not affected the "circuit" excessively.

Since 1821, historical accounts of the origins of electromagnetism seem to have limited their credit assignments for the conception and observation of this electromagnetic "doubling" effect (or "multiplying" effect, if the folding is repeated) to three persons. Almost without exception, however, these accounts have given no specific information as to precisely what each of these three accomplished, what physical form their respective creations took, what experiments they performed, and what functional understanding they apparently had of the situation. The usual statement is simply that a compass needle was placed in a coil of wire.[13] The main purpose of the present review is to recount some of these details.

The following are the three candidates whose names are variously associated with the "invention" of the first constructed electromagnetic instrument, or "multiplier," or primitive galvanometer.

JOHANN SALOMO CHRISTOPH SCHWEIGGER (1779-1857) in 1820 had already been editor for several years of the _Journal für Chemie und Physik_, and was professor of chemistry at the University of Halle.

JOHANN CHRISTIAN POGGENDORF (1796-1877) in 1820 had only recently entered the University of Berlin as a student following several years as an apothecary's apprentice and a brief period as an apothecary. Four years later, he succeeded Gilbert as editor of the influential _Annalen der Physik_, a position he held for more than 50 years.

JAMES CUMMING (1771-1861) in 1820 was professor of chemistry at Cambridge University.

Chronology and Priority

The earliest established date in the "multiplier" record is September 16, 1820, when Schweigger read his first paper to the Natural Philosophy Society of Halle. There seems to be no reason to doubt that this report justifies the frequently used label "Schweigger's multiplier."

In an exuberant support of Schweigger's position, Speter[14] with no mention of Cumming and no hint of "invention" details, shows that Poggendorf in 1821 admitted Schweigger's priority, but suffered some lapse of memory 40 years later when writing sections of his biographical dictionary, leaving a distinct suggestion that the invention was his. Further confusion for later generations resulted from some ambiguous entries in the _Allgemeine Deutsche Biographie_ of 1888. The name "multiplier" seems not to have originated with Schweigger himself. Speter credits it to Meineke as "working" editor of Schweigger's _Journal_, but Seebeck seems to have used it much earlier.[15]

Conceding priority of conception to Schweigger (Cumming has not been a real competitor on this point) does not alter the fact that all three seem to have reached their results independently of one another, that the first work of each on this subject was published within a period of five months, that there were significant differences in their conceptions of the uses and the optimum design of their devices and that between them they provided an adequate foundation for the subsequent development of the galvanometer to become the primary electrical-measuring instrument.

In the matter of publication, Schweigger, as editor of what was popularly called Schweigger's _Journal_, had an obvious advantage, and presented his experiments beginnings on page 1 of the first volume of his _Journal_ for 1821, published January 1 of that year.[16] Oersted's paper had appeared two volumes previously. He began by referring to Oersted's discovery as "the most interesting to be presented in a thousand years of the history of magnetism." He was, in fact, so impressed with the epochal nature of Oersted's achievement that he commemorated it by giving his _Journal_ a second title so that "volume one" of the new title could begin in the year after Oersted's publication.

Poggendorf, as a relatively junior student, had no such easy access to publicity, but he had a staunch admirer in one of his professors, Paul Erman at the University of Berlin. Erman added a seven-page postscript on Poggendorf's invention to his book _Outline of the Physical Aspects of the Electro-chemical Magnetism Discovered by Professor Oersted_, published before April 1821,[17] with an introductory paragraph:

Herr Poggendorf, who is one of the most excellent ornaments of the
lecture room and laboratory of the University here, carried out a
very coherent and well-conceived investigation of electro-chemical
magnetism, leading step-by-step to a method of amplifying this
activity-phenomenon by means of itself.

The postscript begins by referring to the "condenser [_Kondensator_] just brought to my attention by Herr Poggendorf" and explains that he cannot release his treatise "without preliminary announcement of this subject of the highest importance." (It can be inferred from the text that the name "condenser" was chosen because of the device's enhancing of magnetic measurements analogously to the enhancing of electric measurements by Volta's electrostatic "condenser.")

Immediately on reading the book, Schweigger published extracts, mainly of the postscript, with indignant comments on Erman's remissness (or worse) in having failed to mention Schweigger's prior work.[18]

However, Erman was not alone in his unawareness, if it was that, of Schweigger's discovery.

Rival editor Gilbert of the _Annalen der Physik_ reviewed Erman at much greater length than Schweigger, reprinting most of the postscript with evident enthusiasm, and stating in his preamble that the invention is attributed to "a young physicist studying here in Berlin, Herr Poggendorf."[19] Only in a footnote is the reader directed to another footnote in the next article in the volume, where Gilbert finally states that he "cannot leave unmentioned the fact that this amplifying apparatus seems to be due to Herr Professor Schweigger." He then quotes rather fully from Schweigger's first two papers.[16] Oersted in 1823 explained the situation thus: "The work of M. Poggendorf, having been mentioned in a book on electromagnetism by the celebrated M. Erman published very shortly after its discovery, became known to many scientists before that of M. Schweigger. This is the reason for the same apparatus carrying different names."[20]

The same confusion is well illustrated by the paper to which Gilbert attached his confessional footnote mentioned above. Written by Professor Raschig of Dresden, on April 3, 1821, the paper is entitled "Experiments with the Electro-magnetic Multiplier," but the device, throughout the paper, is repeatedly referred to in the phrase "Poggendorf's condenser, or rather multiplier," an awkward combination that suggests editorial intervention.[21]

The work of James Cumming at Cambridge is described in two papers which he read to the Cambridge Philosophical Society in 1821, which were then duly published in the _Transactions_ of that Society. The first, "On the Connexion of Galvanism and Magnetism," was read April 2, 1821,[22] and the second, "On the Application of Magnetism as a Measure of Electricity," was read a few weeks later on May 21st.[23]

Though he quotes some unrelated 18th-century experiments by Ritter in Germany, an 1807 publication of Oersted's, and electromagnetic experiments with solenoids performed by Arago and Ampère in late 1820, Cumming makes no mention of Schweigger or Poggendorf, and never uses the word "multiplier." It, therefore, seems probable that his work was done without knowledge of the German publications or inventions.

Original Electromagnetic Multipliers

Of the three sets of instruments made, respectively, by Schweigger, Poggendorf and Cumming, those of Schweigger are the most elementary, and the least realistic from a practical point of view. He makes little effort to investigate the effect of any design parameters, but presents some odd conductor configurations that involve unimportant variations of the basic principle. The following extracts from his first three papers[13] contain the major references to his conception, construction, and use of his multiplier.

PAPER READ IN HALLE, SEPTEMBER 16, 1820

That a powerful voltaic pile is required for these experiments (of
Oersted) I have confirmed in my physics lectures, using an electric
pile that was so strong it would easily produce potassium metal the
second and third day after it was built. However, I soon saw that
the electromagnetic effect was related, not to the pile, but to the
simple circuit, and I was thereby led to perform the experiment with
much greater sensitivity. To amplify these electromagnetic phenomena
of the simple circuit it seemed to me necessary to adopt a different
arrangement from that initiated by Volta, in order that the
electrical phenomena of his simple circuit might be raised to a
higher degree.

Since a reversal of the effect occurs according to whether the
connecting-wire lies over or under the needle, and likewise
according to whether the wire leads from the positive or negative
pole, thence I say it is an easy inference that a doubling of the
effect is attainable, which is verified in practice.

I present to the Society the simple "doubling apparatus"
[_Verdoppelungs-Apparat_], where the compass is placed between two
wires passing around it. A multiplication of the effect is easily
obtained when the wire is not just once but many times wound around.
A single turn suffices, however, to demonstrate Oersted's
experiments, using small strips of zinc and copper dipped in
ammonium-chloride solution.

Amid innumerable, rambling theorizations (such as, that "hydrogenation affects magnetism as oxidation affects galvanism," or "sulphur, phosphorous and carbon are especially significant in magnetism, since iron in combination with any of these inflammable materials becomes a magnet-material"), Schweigger announces that he looked for the reactive force of the needle on the connecting wire in the simple Oersted experiment, and that he used his "amplifying apparatus" to look for magnetic effects from an electrostatic machine, but without success in both cases. He suggests that he will continue with many more electromagnetic experiments because "with the use of the doubling-apparatus, the needle, instead of needing for excitation a cell capable of generating sparks, approaches more closely the sensitivity of a twitching nerve." However, "additional special experiments are required to find to what limits the amplification can be increased by the method I have created in the construction of this doubling-apparatus, using multiple turns of wire."

PAPER READ IN HALLE, NOVEMBER 4, 1820

[The first half of this paper describes successful observations of the reaction-force of a magnetic needle on the connecting wire of a voltaic circuit, achieved by pivoting the connecting wire in the form of brass needles above and below the compass needle. Though the multiplier configuration of needle and wire is in fact present here, Schweigger does not mention it, evidently regarding this as a separate project. He continues.]

In my lecture of September 16th, I showed that Oersted's results
depend, not on the voltaic cell, but only on the connecting circuit.
The principle I have used for amplification of the effects, for the
construction of an electromagnetic battery as it were, was the
winding of wire around the compass, and I now present to the Society
a bow-pattern of multiple-wound, wax-insulated wire, Figure 3.
[There were no illustrations with Schweigger's first paper.] While
a single wire, using the weak electric circuit here, deflects the
magnetic needle only 30° or 40°, if the compass is placed in one of
the openings of this pattern, the needle is deflected 90° to the
east, or in the other opening 90° to the west, using the same weak
electric circuit....

The "bow-pattern" device has novelty interest only, adding nothing to the elucidation of the multiplier phenomenon. The same is true of Schweigger's next proposal, shown in figure 4. "... I will now add another apparatus, which is just an extension of the previous one, whereby the needle can take up any angle from 0° to 180°." A short length of circular glass tubing, of inside diameter large enough to contain a compass needle, stands with its axis vertical and has single or multiple loops of wire wound on it in vertical diametral planes. In the illustration, successive plane coils are inclined at 30° to one another. "... the electric current flows through the whole wire, and the needle moves under all of these currents, and coming always into another loop can take any desired angle."