Chapter XIII: TECHNOLOGY.--Future Prospects for Gas Companies.--By Mr (2)

It was furthermore found by these experiments, on comparing the crushing resistance of a full-sized column with that of a portion of the same, perhaps two feet in length, that the results were practically identical, likewise that within the limits of construction used for these columns the question of flexure did not enter at all in the problem, but they gave way by direct crushing, and that the resistance to crushing was proportional to its load upon the minimum cross section.

The precedents of safe construction in this matter show that wood columns in mills have successfully sustained for many years a load of six hundred pounds to the square inch without deterioration. As the resistance of such columns is proportional to the cross section, the results of these experiments have changed the practice of mill engineers in the matter; and square columns are of almost universal use, which interfere with no greater area on the floor than the round column of the same diameter, while they furnish an increased resistance of a little over twenty per cent. in excess.

Along the axis of such columns a hole of about one and one-half inches in diameter is bored, and near each end a couple of transverse holes, generally half an inch in diameter, furnish means of ventilating the inside of the column for the prevention of dry rot and also checking, due to contraction and seasoning.

There are several methods of laying the floor plank upon these beams, which are placed from eight to ten feet apart, according to the dimensions of the machinery to be placed in the mill. The first floor of three-inch plank, planed on one side and grooved on both edges, is laid planed side down, and the hardwood splines are inserted into the grooves before the planks are pressed up and spiked to the beams. An agreeable finish is sometimes arranged underneath by plowing a rabbet in each of the corners, and inserting a bead in the groove thus formed, which is secured by nails driven diagonally into the plank on one side only, because if the nails were driven into both sides, the bead would be split by the contraction of the plank.

These planks should be cut to sufficient length to cover two bays of the mill; and their transverse resistance is that of a beam fixed at one end and supported at the other, or one and three-fifths as much as a plank of the same size but half the length would support; but it should be remembered in this connection that, if evenly distributed on the floor, five-eighths of the load would be carried by every alternate beam unless the planks are so laid to break joints at convenient intervals of about three feet.

The top flooring is generally laid directly upon the floor plank, with one or two thicknesses of roofing paper interposed; but the preferable method, which deadens the sound and vibration, and also greatly increases the fire-resisting qualities of the structure, is to lay a coat of mortar on the floor plank, preserving the uniform thickness by means of furring placed about sixteen inches apart, and then to lay the upper floor upon this.

For these upper floors hardwood plank, one and one-fourth inches thick, and not over four inches wide, is used. The black birch is considered by many to possess the greater resistance to wear; and Southern pine is ranked next, although the latter wood gives trouble by stringing, especially when trucks are rolled over it. White maple forms an excellent top floor, although not so hard as others, especially where the floor is likely to be exposed to water, as in paper mills and bleacheries.

ROOFS.

Benjamin Franklin once said that next to a good foundation a good roof was the most important feature of a building. Although the constructive features of mill roofs are well defined, yet with regard to roof covering there is a wide diversity of experience and opinion.

The present form of factory roofing resembles a floor in its construction, being made, in a similar manner, of plank laid upon beams which project through the walls, where they act as a bracket to the cornice, the ends being sawed after any suitable ornamentation. The inclination for such roofs is about three-fourths of an inch to the foot. Where a mill is narrow enough for a single beam to reach from the wall to the ridge, they form cantilevers, the second point of support from the wall being by the columns one-third of the distance across the mill, and the ends of the beams are further secured together by means of iron dogs. For mills of greater width, the beam would reach only to the row of columns, and over the middle of the mill a beam is placed, usually horizontal on the under side, and hewn down from the middle to each end, so as to preserve the same slope on the upper side of the beam as for the roof.

In many instances mills are built with brick cornices, without any of the wood projection from the side; and in other buildings the walls are carried above the roof, which slopes toward the center, and all water falling on it or melted from the snow is conducted from it by pipes leading down through the middle of the mill.

It is not desirable to place gutters around the edge of the mill, as they serve no useful purpose, and are in continual need of repairs. By leaving the edge of the mill plank square and protecting it by sheet metal flashing, the rain falling from the roof can be received by a concave walk of coal tar concrete placed on the ground around the building. Suitable porches over doors, or some guard on the roof at these points, will prevent people who may be passing in at doors from being unduly wet by water from the roof.

There are numerous forms of roof coverings, the use of the different varieties being to a great extent local; that is, the sheet iron coverings used in the Middle States are almost unknown in New England; and in the latter place the ordinary tinned iron roofing is universally painted, while in the Dominion of Canada it is laid obliquely and never painted.

It is conceded by all that sheet copper forms the most desirable method of covering a roof; and, if one could be assured of the permanence of the structure, irrespective of the necessity for making changes every half year in order to keep pace with the march of invention, it would doubtless be shown that under such conditions of permanency copper would form the cheapest roof.

The most widely used roofing materials for this class of buildings are the asphalt and the coal tar roof, the latter being the most widely used in New England. There are numerous varieties of these composition coverings, which are applied by various methods. Some of these are of the most satisfactory character, while others are poorly designed and unskillfully applied, and are a constant source of trouble and expense to the occupant of the building.

One of the leading manufacturers, the efficiency of whose work for many years over a large amount of mill property I can vouch for by personal knowledge, uses the following method of applying the roofing. Three layers of roofing felt are placed on the plank parallel to the eaves, and continued by lapping each additional layer two thirds of its width upon the preceding one, and in this manner covering the roof with three thicknesses of the felt, breaking joints. This is secured to the roof by nails through tin washers and coated with a melted composition, and then two additional layers of felt are placed over the whole. Another coat of composition is then applied and gravel is placed over the whole while soft.

This maker does not approve of the practice of cementing each sheet of felt when it is laid, because it does not allow the felt freedom to yield from the expansion and contraction of the roof. When tin is applied to roofs, resin-sized building paper should first be laid on the roof plank, and the sheets of tin should be painted on the lower side before being laid.

Of late years cotton duck has been applied as a roof covering, and has been watched with a great deal of anticipation, although it has been used for similar purposes in covering ships' decks for many years. But the two uses are not strictly comparable, because the ship's deck is calked tight, and therefore the covering is free from the application of moisture underneath, while the roof is never tight, and the warm air underneath, heavily charged with moisture, which permeates the cracks between the planks, becomes chilled and condenses as it nears the top, carrying on a process of distillation.

As an example of the extent to which this can be carried on, I have known of instances where people presumed they were making a good roof by leaving slight air spaces by means of the furring laid between the roof plank and the top boarding. The circulation of air in these spaces deposited sufficient moisture to rot the boards.

A mill manager, wishing to have a roof over a very warm room, which should be both tight and a very perfect non-conductor, made a roof containing a space of about sixteen inches, which was filled with sawdust, and the roof boarding on top of this was covered with tar and gravel in the usual manner. In a few weeks the water began to drip through the ceiling as if the roof was leaking, although there was no snow on the top of the roof. Investigation showed that within that short time a sufficient amount of water had condensed with the sawdust to saturate the whole.

I would say in this connection that three inches of plank afford an ample protection against condensation over any ordinary process of manufacture, although four inches of plank have been used as a roof over paper machines in order to be safe beyond peradventure; but it is necessary that nails should not be driven into the bottom of this roof plank, because the point of a nail will reach to a lower temperature near the outside of the roof in the winter, and being a better conductor, it will cause moisture to condense upon the head of the nail.

Tin roofing is so general in use as not to require any allusion to methods of application, but the only course to reach economical and satisfactory results for a term of years, especially for locations near to the sea shore, is to use the best quality of dipped roofing plates of some brand which can be relied on as conforming to the standard and free from "wasters" or imperfect plates.

Duck roofing has been successfully applied by first laying and tacking down a covering of two-ply asphalt paper, and upon this was spread a covering of resin-sized sheathing paper, tacked in the usual manner. Upon this was laid a covering consisting of cotton duck, forty-four inches wide and weighing twenty-six ounces to the yard. Several methods of joining the edges of the duck together have been tried, resulting in the abandonment of the method of sewing used, for the preferable method of nailing the duck down, laying one strip over the other, and then opening the duck, a lock joint is formed without any jointure between the two sheets exposed to the weather. After the duck is stretched on the roof, it is securely fastened by means of round-headed woodscrews, one and one-fourth inches long, through a concave tin washer three-fourths of an inch in diameter, resting upon a seven-eighths of an inch washer made of roofing felt.

A coat of hot pine tar with a small quantity of linseed oil is laid upon the whole of the duck roofing, after being laid, for the purpose of filling the fiber and preserving the cotton fabric by means of the antiseptic principles of the pine tar. The surface is then covered with two coats of mineral paint.

Within a year, paper has been very successfully used as a roof covering. Sheets of wood pulp board about one-sixteenth of an inch in thickness are treated by a process which renders them hard and elastic, and secured upon the roof by means of tacks through concave tin washers. The edge of each sheet is grooved, in order to allow for the expansion and contraction of the roof. The whole roof is then covered with a heavy mineral paint. Experience with this during the past severe winter in Maine has been of the most satisfactory nature.

Shingles furnish a much better roof covering than slate, both in the matter of conduction of heat or cold in the extremes of summer and winter and also in resistance to fire. The heat of a slight fire underneath the roof will cause slates to crumble; and the same result will be obtained by heavy sparks falling and burning upon the roof. Some people treat shingles by boiling them under pressure in a solution of salt and chloride of lime, for the purpose of antiseptic treatment and also to render them fireproof.

STOREHOUSES.

The latest form of storehouses tends to one of two extremes. Where land is nearly level, and cheap, the greatest storage capacity can be obtained with the greatest economy by means of a one or two story storehouse built with a plank construction, with the beams secured to the posts by means of knees. A traveling crane or railroad runs along the middle of the storehouse, affording a ready means for rapid changes of the contents of the storehouse.

Another form for storage is by means of very large brick buildings, especially arranged as a protection against outside fire. In designing a storehouse it is of especial importance that the stories should not be made so high that it will be possible for a dangerous load to be piled upon any one floor.

The wool storehouse of the Pacific Mills at Lawrence can be safely said to be in its design and construction the finest example of mill engineering in the country.

Another type of mill storehouse, designed for both raw material and finished goods, is designed by Mr. John Kilburn, of Lowell, and consists of two buildings placed at right angles to each other, and joining only at one corner. These buildings do not contain openings through the floors of any nature whatsoever, either for stairways, elevators, or any other purpose; but all vertical communication is furnished by means of a masonry tower at one corner of the buildings, which contains an elevator and stairway. At the level of each floor, substantial balconies lead through a doorway in the tower to one in the storehouse, and the storage is added to or withdrawn from the storehouse in this manner.

I have not made any reference to the use of rolled iron for structural purposes, because such material has not been used to any extent in mill architecture. Irrespective of questions of space or of strength, wood beams possess advantages in the reduction of vibration, facility of securing the plank above and hangers below, and a great many other purposes in the changing and alterations of a mill, which render them peculiarly useful, and I believe that the results with Southern pine beams in American mills are much superior to those of the iron beams in European mills.

No small part of the success attending the use of rolled iron in the structural purposes for which it is adapted, has been due to the excellent and reliable engineering information contained in the manuals and catalogues issued by the rolling mills. Such works are reliable and clear, and, as far as I know, can without exception be safely followed.

The general tendency of American mill construction is toward as low buildings as the price of land will admit. The American mills being devoted to a large variety of operations, instead of being confined to a single process after the manner of those of European type, require a great deal more care in their organization, not merely in the original lay-out for the purpose of arranging for the passage of the stock in processes from the raw material to the finished product in as straight lines as possible, but due consideration should also be given to providing facilities for the enlargement of the mill.

As an illustration of the methods employed, in a paper mill plan of my own design, [the view and plan being thrown on the screen], the various operations containing processes of different hazard in regard to fire are completely isolated from each other by means of fire walls, and the storage of the mill is in turn isolated from the manufactory.

The storehouse consists of three sections, the largest section for paper stock, which is sorted in the upper story, the second section, one story in height, for other manufacturing supplies, and beyond the fire wall the storehouse is arranged to contain the finished paper. Goods can be taken away from or added to the storehouse at the single line of teams, or railroad siding.

After the stock leaves the sorting room, it is carried to the dusting room over a covered bridge, which is protected from the weather on one side, yet does not form a flue for the spread of fire as does a closed bridge.

The first room in the main mill is used for a dusting room, and thence the stock falls into the rotary bleach, whence it is carried through the fire doors to the engine room. Here it meets the wood pulp and clay wheeled from the middle section of the storehouse, which is on that same level. After washing and beating, the stock is run into the drainers below, whence it is raised again, and after suitable intermediate processes the pulp is converted into paper on the paper machine in the connecting building. This paper is then taken into the upper part of the main building, and after being dried on the lofts is suitably calendered and packed before being transferred into the extreme end of the storehouse to await shipment.

At the present time it has been found that an inclined roof of the olden type is not a necessity over a paper machine, as has been decreed by the tradition passed down from old practices. Within the last year, a number of flat roofs have been placed over paper machines, without any trouble ensuing from condensed water forming on the ceiling and thence dropping upon the stock. It is well known that the use of a flat roof in such places is attended with a great many mechanical conveniences; and the pitched roof hitherto used for these purposes has been submitted to, only because it was presumed to be necessary. The whole tendency of mill design is in the line of fitness of means to ends, in the simplest and most direct manner.

When the mills in Lowell were first built, they consisted of isolated buildings, which it was presumed would remain for all time; but when it became necessary to increase the plant, it was found that the engineer had wisely laid out the mills in the same yard in reference to a fixed grade, so that corresponding floors would meet when the buildings were extended so that they reached each other.

Wherever a strong and diffused light is necessary for any manufacturing process, or the conditions are such as to require unusual stability of the building, one-story mills lighted by monitors afford accommodations not reached by any other form of construction.

In presenting before you some of the salient features of modern mill construction, I have endeavored to show the various steps of progress leading up to the development of the present types of design, as well as some of the methods of construction in present use.

These various steps in advance, producing mills better suited for the purposes for which a mill is built, are not generally due to elements originating with the manufacturers, but with the Factory Mutual Underwriters, who, finding it cheaper to prevent a fire than to settle a loss, have in every manner encouraged improvements in construction, equipment, and administration, with the result of diminishing the insurance on textile manufacturing property during the last generation from two and one-half down to one-fourth of one per cent., or reducing the cost of insurance eighty per cent.

In designing any work, a careful regard should be given to precedents, remembering that a good designer must also be a good copyist.

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THE PASSIVE STATE OF IRON AND NICKEL.--E. Saint Edme.--The nickel of commerce immediately becomes passive if immersed in ordinary nitric acid. Iron, while being briskly attacked by common nitric acid, is rendered passive by contact with nickel. If steel and nickel are plunged into the acid together, the former metal is not even momentarily attacked. Nickel retains energetically a proportion of combined nitrogen, to which its passivity is due.

IMPROVED TORPEDO BOAT.

We give an illustration of the new type of second class torpedo boat which Messrs. Yarrow & Co. have recently constructed to the order of the Admiralty, and which was tried at the latter part of last year. The boat is 60 ft. long over all and 8 ft. 6 in. wide, 3 ft. shorter and from a foot to 15 in. wider than the old type of second class boats. She attained a speed of rather more than 17 knots per hour on her official trial with 4 tons on board. The speed, when light, for six runs on the measured mile was 18-1/2 knots. The latter seems a very high speed for so small a vessel, and indeed it is a remarkable performance, but at the same time the speed of 17.031 knots on a four hours' trial with 4 tons on board is more remarkable still. It is well to note, says _Engineering_, in comparing speeds of torpedo boats, under what conditions as to weight carried and duration of running the trial is made. In our previous notice we referred to the manner in which this boat differs from ordinary second class boats in the manner of ejecting the torpedo; and the arrangement is well shown in the engraving. The more ordinary method of firing the torpedo from a tube or tubes, built into the hull and pointing forward through the bow, will be familiar to the majority of our readers; but here it will be seen the bow fire has been altogether abandoned, and a swiveling gun placed aft is substituted. The gun, of course, is not new; indeed, one was placed on the old Lightning, the first torpedo boat built for the English navy. That vessel was, however, a first class boat, and although not so large as the first class boats now built, was considerably bigger than No. 50, which is the official designation of the craft under notice. In the Lightning, too, the torpedo gun was placed forward, and was trained in quite a different manner to that of this second class boat. We have already commented on the offensive advantages of being able to eject the torpedo through a wide angle of range, and when going at speed, rather than having to bring the boat to a stop and fire only end on. We need not therefore recur to this point; but since our former notice appeared we have had, while on shore, an opportunity of seeing the boat steam at speed and maneuver. Our previous experience was obtained on board--a position which, in some respects, does not afford so good a point of observation as when one is at some little distance from the boat. It is certainly a remarkable sight to see the manner in which this little vessel winds among craft or round buoys, or turns circles of surprisingly small diameter. She seems to pivot on a point very near the bow, a fact which is no doubt chiefly to be accounted for by the way the deadwood is cut away aft. This allows the stream of water diverted by the unusually large rudder to swing the after part round with facility.

Another notable feature about No. 50 is the comparatively small bow wave she throws up. We believe it is pretty generally acknowledged now that the most noticeable point at night about a torpedo boat traveling at high speed--putting on one side flame and sparks from the funnel--is the high bow wave the majority of these vessels throw up when going quickly through the water. The powerful electric search light causes this mass of foaming water to show up with peculiar distinctness against the dark background of sea and sky. It has been, therefore, thought advisable to reduce this undesirable feature even if something in the shape of speed has to be sacrificed. Fairly full bow lines are the best for fast boats of this class, but in such a model the big bow wave is very noticeable. Messrs. Yarrow have met the demand of naval officers for a less easily observed boat by placing the greatest cross section further aft than they would have done had speed alone been the point aimed at, as it almost always was in the earlier torpedo boats. It is therefore additionally creditable to Messrs. Yarrow that they have reached the unprecedentedly high speed of seventeen knots, with so considerable an addition to the beam, and that they have at the same time reduced the bow wave.

There is a further advantage of less surface disturbance when running torpedo boats. It is unnecessary to point out that surprise will be the chief element of success in future possible attacks in which these craft may be engaged. As the bow wave is most likely to reveal the presence of the boat by sight, so also will it most probably give first warning of approach by sound. It is the splash of the water and not the noise of the machinery that can be heard for the greatest distance when a boat is running with hatches closed--speaking of course of high-speed boats in which the engines are kept to a high degree of perfection, as they should be, and in the Royal Navy are, with all torpedo boats. It will therefore be seen that there is an additional reason for reducing the objectionable bow wave.

The boat which we illustrate recently made the run from the Thames to Portsmouth, and, the weather being bad, was taken through the somewhat intricate but more sheltered fairways and channels of what is known as the "overland passage." Off Margate she managed to get on the ground--a result by no means to be wondered at; and, as the sands here are very hard, she smashed her propeller. After a time she was got off and beached, when a new propeller was fitted. We mention this incident, as it is generally supposed that these craft are of a very fragile description; "egg shell" is the favorite term of comparison. One distinguished naval officer--retired--has said he would never willingly go on board these craft, for fear of putting his foot through the bottom; and there is a very funny story extant about a sailor with a wooden leg. It would seem, however, from the experience of No. 50, that steel vessels are of much more robust constitution than is generally supposed, and, indeed, there is ample testimony to the fact. We recently witnessed the efforts of a small working party to get one of these vessels over a bank. She was pushed as high up as the strength of the party would allow, and in this position her fore part was over the bank for about a third of the length of the boat. A tackle was then put on the bow, which was bowsed down until the boat could be dragged straight ahead.

A few words may appropriately be added here as to torpedo boat policy generally. Admiral Colomb, in the opening remarks of his excellent little manual, "The Naval Year Book," refers to the torpedo boat question in the following terms: "The fleet, the flotilla, the cruiser, and the harbor attack and defense have each had (_i. e._, during the past year) their share of attention, and developed exercise, and opinion has been advanced, guided, or turned back by the observation of facts which these exercises have brought out. While it cannot, perhaps, be said that the torpedo, as torpedo, has much altered its position in naval estimation, it seems fair to assume that the torpedo boat, as boat, has fallen in repute. In the first, it has grown very much larger, and has, in point of fact, ceased to be a boat. In part this may have come about because the _role_ which some proposed for the torpedo boat, of being an entirely defensive weapon confined to territorial localities, and operating only within a short distance from its port, has never been generally accepted. Boats which were never intended for voyages have been sent on voyages, and, being found more or less unsuited for that kind of service, supposed improvements have been made, so that they should be capable of executing it. The 'harbor defense' instrument has become a 'sea attack' instrument, and in some sense an unrecognized rival to the undoubted sea-going torpedo vessels like the Archer, the Fearless, and the Rattlesnake."

In these passages Admiral Colomb has put the present aspect of the torpedo boat question very aptly. We are now experiencing the inevitable reaction consequent upon our early over-valuing of the torpedo. The unknown possibilities for distinction of those weapons were so magnified that scarcely any expenditure was thought too great to provide means for their employment, both in and out of season. Torpedo vessels have been growing in size and costliness. More and more gear has been crowded into them, increasing their weight and cost, and also the intricacy of their machinery. In all this, cheapness, the one great virtue of the torpedo, has been overshadowed. No doubt it is right for a great naval power like Great Britain to have vessels of all classes, and the possible value of small fast vessels such as the Archer or the Rattlesnake--not necessarily as connected with the torpedo--can hardly be overestimated. But for smaller naval powers, that look on the torpedo boat as a means of coast defense, especially those countries having a broken coast line studded with islands, bays, and inlets, it is very questionable whether the smaller boats, such as that now under notice, will not be a better investment than the larger craft at present more in vogue. By the additional seaworthiness of this boat, secured chiefly by the increased width, the 60 ft., or second class, boat has been lifted into the category of practicable vessels; and it must be remembered that four or five of these smaller craft can be purchased for the price of one modern first class boat. This is the crucial point, the money standard, and it is to that that all ship and boat building questions must be reduced, whether it be in wealthy England or the most impecunious and perhaps hardly more than half-civilized state.

The question may be argued from many points of view, and we put forward these remarks simply as suggestions, without any wish to dogmatize. But it seems that, as the cheaper second class boat has been carried so many steps in advance, it may be worth while to reconsider the position with a view to returning to the original torpedo boat idea of small, inexpensive vessels, acting by surprise; and not putting too many eggs in one basket.

SCIENTIFIC APPARATUS AT THE MANCHESTER ROYAL JUBILEE EXHIBITION.

_Sine and Tangent Galvanometer._--An exhibit of original scientific apparatus was contributed by Prof. G. F. Fitzgerald, of Trinity College, Dublin. The first instrument was a sine and tangent galvanometer, which combines both instruments, and has four interesting peculiarities: (1) The windings of the coils are visible through the plate glass sides, so as to be capable of easy measurement _in situ_. (2) The position of the needle is read by reflections of a cylindrical scale in two rectangular mirrors whose intersection is horizontal, and which are attached to the magnet. These mirrors reflect images of opposite sides of the scale to a fixed mirror which reflects them into a microscope, in which, by means of a micrometer, it is possible to read accurately the position of the line which is the same in the two images. (3) This cylindrical scale is affixed to the base of the instrument, and the coils can be rotated round it, so that when the instrument is used as a sine galvanometer its position is read by reflection in the rectangular mirrors attached to the magnet of a pointer attached to the coils. (4) By a slight modification of the suspension, a beam of light can be reflected from a mirror connected to the magnet at 45 deg. to its axis of rotation, and can emerge through the plate glass side of the instrument and fall on a horizontal scale, where it will measure the tangent of the deviation instead of the tangent of twice the deviation, as in ordinary reflecting galvanometers.

The meldometer shown is an instrument for facilitating the identification of small quantities of minerals by comparative observations on their melting points, and for observing the phenomena of their fusion and ebullition. It consists of a strip of platinum arranged to traverse the stage of a microscope, and heated by a current derived from two Grove's cells.

On this strip the fragments of the mineral, or, if for comparative observation, of two or more minerals, are placed. The temperature of the platinum is then raised by gradually diminishing a resistance placed in circuit with the battery and meldometer, the behavior of the substance being meanwhile observed through the microscope. To effect the elevation of a temperature automatically, a resistance, consisting of a rod of carbon fitted in a vertical glass tube, is employed. Professor Fitzgerald showed two sets of apparatus for measuring the densities of gases. Both methods depend on the determination of the amount by which a body is buoyed up when immersed in the gas.

_Model for Illustrating the Properties of the Ether._--A very interesting exhibit was the model for illustrating the electromagnetic and luminiferous properties of the ether, of which a detailed description is almost necessary. The model consists of a series of wheels, rotating on axes fixed perpendicularly in a plane board, and connected together by India-rubber bands. The axes are fixed at the intersections of two systems of perpendicular lines, and each wheel is connected with each of its four neighbors by an India-rubber band. Thus all the wheels can rotate without any consequent straining of the system if they all rotate at the same rate. If, however, some of the wheels are rotated through a different angle from others, the India-rubber bands will be strained. If it be desired to represent a region in which conducting matter exists, it will be represented by removing the bands from a set of wheels. Suppose the bands are removed from the regions, A and B, and from the connecting line, A B, then we can represent the charging of these regions with opposite electricities by introducing some mechanism by means of which the wheels on opposite sides of the line, A B, can be rotated in opposite directions. The model is not intended to illustrate in any way the connection between the ether and matter; indeed, one of the advantages claimed for the model is, that the study of it so distinctly emphasizes the distinction between the phenomena depending on the general properties of the ether by itself and those depending on its connection with matter. For instance, from the very case we have just considered, we get impressed upon us that it is by means of matter only that we can get a hold on the ether so as to strain it. As the object is not to illustrate the connection between matter and ether, any rough method of turning the wheels so as to create the proper strain will do well enough, as it is not the method of producing, but the nature of the strain produced that is to be considered. Having once rotated these wheels, we may replace the bands along the line, A B, and we have the state of the ether between two oppositely electrified bodies represented on the model.

It will be observed that half the India-rubber bands are strained, and that in lines running round the bodies the tight side of a band is always away from one body and next the other. This represents the polarization of the ether. The late Prof. Clerk-Maxwell defined polarization as a state in which the opposite sides of each element are in opposite states. Now, the opposite sides of each band are in opposite states--one side loose, the other tight; and so it can very well represent the polarized state of the ether. The displacement producing the polarization is due to the different rotation of the wheels carrying the band causing more of the band to be at one side of the wheels than at the other--less at the tight and more at the loose side of the pair of wheels, and this represents the electric displacement producing the polarization. The direction of this displacement is at right angles to the line of the bands that are strained, and is out from one body and in toward the other all round.

Considering the other properties of the ether that are represented by the model, we observe in the first place that during the time polarization is taking place the wheels are rotating, and that the rate of rotation of the wheels is proportional to the rate of increase of polarization, and that the direction of the axis of rotation is perpendicular to the direction of the displacement. Hence it is seen that the magnetic force is properly represented by the rate of rotation of the wheels, and its direction by the axis of rotation. The model, although simple in construction, is very useful, and its careful study will greatly assist the student in obtaining definite physical conceptions of many of the more abstruse phenomena depending on the ether.

_Prismatic Photometers._--Another exhibit was a photometer made of solid paraffin, or any other translucent substance, invented by Mr. J. Joly, of the University of Dublin. The arrangement is at once simple and effective. The instrument depends upon the fact that if a prism be cut from a translucent body, and so exposed to a source of light that one only of its faces is illuminated, the light diffused through the substance and reflected out through the illuminated faces of the prism gives it an appearance as if lighted up internally. The effect is, in fact, as if the prism itself was a source of light. Two such prisms laid together on smooth faces, and receiving light from separate sources, if placed so as to be at opposite sides of the plane of division, appear as if each was emitting light proportional in intensity to the source of its supply. The double prism has the appearance of two luminous bodies laid side by side.

When, however, the supply to each prism is brought to equality, they appear as if emitting equal quantities of light; and it is hard to detect any longer that two prisms are being observed, so completely does all trace of the plane of division disappear. An ingenious piece of apparatus invented by Mr. Joly was one for carrying out his method of determining the specific gravity of small quantities of dense or porous bodies. The method here shown enables the specific gravity to be determined whatever the density or state of aggregation of the substances, and in extremely minute quantities, with an accuracy limited only by the sensitiveness of the chemical balance.

_Telegraphing the Readings of Scientific Instruments._--Another invention of Mr. Joly was his apparatus for obtaining telegraphically the readings of meteorological instruments placed at a distance from the observer. This apparatus may be attached or adapted to the various thermometers, the barometer, rain gauge, and to other instruments placed in a mountain station, thus enabling their readings to be taken from a conveniently placed observatory. Any number of instruments may be worked with perfect reliability and certainty by the use of three wires only; the only extra piece of apparatus needed being a disk, carrying insulated contact pieces arranged round its circumference, to which the wires of the different instruments are attached. Of these three wires, one serves to put one after the other of the contacts into circuit with the home station through the second wire. By this second wire the readings are taken and the readjustment of the instruments effected. The third wire is for the indication of the contacts, and is taken from all the instruments to the galvanometer in the home station.--_Industries._

COLORED PHOTOGRAPHY.

About nine months since we directed attention to the system of colored photography invented by Mr. J. E. Mayall, London. Since that time, Mr. Mayall has further developed the details of his process, and as a result his color pictures have been much improved both as regards appearance and size, and are beautiful specimens of this new departure in photographic art. As stated in our previous notice, Mr. Mayall, after fourteen years of experimental research, has discovered the art of reproducing the colors latent in the negative of the photograph, having arrived at his discovery by the aid of spectrum analysis, which led him to the conclusion that every color in the organic world, when exposed to a suitable photographic plane in a camera, registers exact vibrations. Mr. Mayall has succeeded in producing chemical colors extremely attenuated, which exactly correspond with the vibrations in the negative. In doing this, he keeps the film alive to the smallest vibrations of light. He uses, first, lactate of iron to impregnate the isinglass film with a salt of iron capable of uniting with any stronger organic acid; and, secondly, meconic acid, which impregnates the film of albumen, and has a stronger affinity for iron than lactic acid. It unites with the iron, and forms a red film, which is in a state to receive all the lower vibrations of the red end of the spectrum, and this gives these lower vibrations a fair chance with the electric light. All subsequent processes assist this chemical march to the final end of making a print that will take up colors, which, when added, fall in their places, and there remain indelible and unalterable.--_Iron._

FUTURE PROSPECTS FOR GAS COMPANIES.[4]

By Mr. THOS. WOOD, of Sandusky.

Those who were in attendance at our Dayton meeting will perhaps recall the fact that the writer, in a paper read at that time, strongly advocated gas companies taking hold of the electric light business and running the same in connection with their gas business; you will also recall the fact that the writer suggested that gas companies should take up the incandescent electric light and fuel gas. Since that time it has been demonstrated by several gas companies in this and other States that the electric arc system can be added with success, financially, to gas companies and with satisfaction to their patrons; and the writer derives great pleasure in hearing of so many companies who have left the narrow and beaten track of prejudice and are now walking in the broad road of progression.

[4] A paper read lately before the Ohio Gas Light Association.

It is not my intention to dwell upon arc lighting now only long enough to state that, after two years of practical experience with the combination, our company consider they have taken a right step in adopting it, and that it is satisfactory in every respect. Other gas companies that have adopted the arc system can undoubtedly corroborate this with their experience. I would make this paper a continuation of the last one by now taking up the incandescent electric system and fuel gas question. That both will be introduced into every city in the United States before long by some one I have not a shadow of a doubt; and why? Simply because they are both desirable commodities in domestic economy and hygiene.

Please lay aside all prejudice, and I will show you an ideal domestic burner for illumination purposes. Now, what comprises an ideal burner for domestic use? In the first place, such a burner must not blacken our walls and ceilings, neither must it give off deleterious products of combustion; it must be a steady light, and not subject to draughts; it must not give out heat in summer, it must not be possible for inflammable goods to ignite by coming in contact with it; it must be a light that will have no ill effect if by accident the key is left open; it must be a light that our country cousins cannot blow out, neither must it be one that requires dangerous matches to ignite it, and lastly, it must be a fairly cheap light.

Now, gentlemen, if you have thrown prejudice to the winds, perhaps you can recognize in this ideal burner the incandescent electric light for domestic use. Now, if this light is an ideal one, who is going to prevent its adoption by the public? Gas companies cannot, and if they cannot no one can. So, in my mind, the wisest course to pursue is to admit what we know to be true, and proceed at once to supply the demand, increase our revenue, push out into the suburbs of our cities, sell it as cheaply as possible, and don't let others come in and take away what rightly belongs to you. If there is any money to be made in the business by others, there is still more in it for us.

For store purposes, where the hours of burning are defined, I think it better to abandon the meter system and fix a price per annum or month for each lamp, taking into consideration the hours of use as a basis for charges. For private dwellings this would not be practicable, and we would have to resort in this case to meters, or perhaps fix upon a price for furnishing the current and have the consumer purchase the bulbs or lamps whenever renewals were necessary. In this way economy would cheapen the light to the consumer. Any method that will dispense with the meter and still be satisfactory will be the one to adopt.

I cannot understand how some gas companies who have the incandescent electric system as a competitor can console themselves with the fact that it is not injurious to their gas business, even taking it for granted they are selling as much gas as before its advent. Is this a just reason why they should make no effort to secure their old patronage? I think not, for it is human nature to secure a whole loaf in place of the half, when it is possible to get it. A gas company's revenues would certainly be increased by the step, and a dangerous rival would be made profitable.

I think it is a mistake to think that by and by the people will get back to gas. Of course some will, just as gas consumers sometimes go back to coal oil; but, because a few give it up, don't let us deceive ourselves by thinking that all will do it eventually, for the incandescent electric burner is bound to remain wherever it is now in use, and will find its way to the other places where it is not now in use. "That is all very well to talk about," I hear some one say, "but what are they going to do with our prior investment?" To such I would say, push that, too. Cheapen it to its lowest point and urge its use for power and cook stoves until such time that you find yourselves able to supply gas for heating purposes of all kinds.

What difference does it make to a company whether the money expended for improvement account be coal gas benches, holders and mains, or dynamos, boilers, and wire? I fail to see the difference, and if improvements have to be made in both, so much the better--it shows a healthy demand for both branches, and should be promptly provided for.

If arc lighting is to be the light on our streets and the incandescent electric light for our stores and dwellings, shall we have to draw our fires from under our gas benches and stop making gas? This, to the writer, would be an absurd deduction, for the very reason that in nature's laboratory all these elements are placed, and gas would not be one of them if there were not some important part for it to play in the supplying of man's wants. It is for us to take the things we find in nature's laboratory and select the fittest articles for each special use; and it is reasonable to suppose that it will be only the fittest that will finally be a success. The arc light, so far as the writer has ascertained, has asserted pretty generally throughout the country its supremacy on our streets, and this in spite of all opposition from gas companies--showing conclusively that it has gained its position by the force of demand for the fittest. Incandescent electric light is just as surely finding its position and field of usefulness, and in its turn will assert its supremacy, and why? Because it has the qualifications called for in the public specifications. Some will assert that it is too expensive to come into general use, and also that it is not as reliable as gas. The first is no argument against it, for was not coal gas sold at exorbitant prices in its early days? It certainly is capable of being cheapened in the future, as gas has been, and this is one reason why gas companies should enter the business, as it is in their power to cheapen it.

As far as unreliability is concerned, it certainly looks the most serious objection; but don't be alarmed on that score, for duplicate machinery or storage batteries will eventually overcome this bugbear, and while discussing this subject don't let us forget that the breaking of a main, the filling up of a drip, a flood or explosion, or even Jack Frost, has often caused our customers to think that even gas is not very reliable.

I cannot understand what prompts gas companies as a rule to prejudice against electric lighting, unless it be they imagine the outcome to be idle gas mains and cold benches. This I think is all wrong. The largest unoccupied field to-day is the fuel gas field, and who should step in and supply this demand? Could any one do it as well as the present gas companies? We have our mains and services already laid; we have our holders, meters, and trained labor, most of us have also the necessary land to spare on which to erect the generators.

Next to the fuel gas field I think I can see another field nearly as extensive, and that is the coal oil field.

Please imagine the following picture, which is representative of the writer's belief of what a gas company will be in the near future; in fact so near in the future that before our next convention rolls around it will be a reality.

One set of officers, whose principal qualifications shall be progressiveness--their duties to be divided between electric lighting of all kinds, including electric power, fuel gas for all purposes, including gas engines; also incandescent lights off fuel gas mains.

Now let us see what the plant will consist of. One set of mains for fuel gas, from which our patrons will draw all their fuel, and also light, if they wish. Gas engines will be run economically with this gas. One set of meters only will be required.

There will be no coal gas benches as we have them now, as the method of manufacture is too laborious, too expensive and very primitive, not to say barbarous--everything now being built on the horizontal plan, requiring the greatest possible exertion to both draw a charge and stoke. The generators of the future will be on the cupola style, feeding by gravitation from the top. Native coals in all probability will be sufficiently good to make gas of. One portion of the plant will be devoted to the dynamos and engines for furnishing the electric light. Where the coal gas benches now are will be boilers, or perhaps even these will be unnecessary if gas engines be used. If steam boilers be used, they will be fired with producer gas, and the holders will become simply pressure regulators. The revenues of gas companies will be increased fivefold, if not more; the consumer will get cheaper fuel, cheaper power, and cheaper light.