Chapter VI: Part 6

This magnificent instrument stood on the lawn in the rear of Sir
William Herschel’s house at Slough; and some of our readers, like
ourselves, may remember its extraordinary aspect when seen from
the Bath coach-road, and the road to Windsor. The difficulty of
managing so large an instrument--requiring as it did two assistants
in addition to the observer himself and the person employed to note
the time--prevented its being much used. Sir John Herschel, in a
letter to Mr. Weld, states the entire cost of its construction,
4000_l._, was defrayed by George III. In 1839, the woodwork of
the telescope being decayed, Sir John Herschel had it cleared
away; and piers were erected, on which the tube was placed, _that_
being of iron, and so well preserved that, although not more than
one-twentieth of an inch thick, when in the horizontal position
it contained within all Sir John’s family; and next the two
reflectors, the polishing apparatus, and portions of the machinery,
to the amount of a great many tons. Sir John attributes this great
strength and resistance to the internal structure of the tube, very
similar to that patented under the name of corrugated iron-roping.
Sir John Herschel also thinks that system of triangular arrangement
of the woodwork was upon the principle to which “diagonal bracing”
owes its strength.

THE EARL OF ROSSE’S GREAT REFLECTING TELESCOPE.

Sir David Brewster has remarked, that “the long interval of half a century seems to be the period of hybernation during which the telescopic mind rests from its labours in order to acquire strength for some great achievement. Fifty years elapsed between the dwarf telescope of Newton and the large instruments of Hadley; other fifty years rolled on before Sir William Herschel constructed his magnificent telescope; and fifty years more passed away before the Earl of Rosse produced that colossal instrument which has already achieved such brilliant discoveries.”[25]

In the improvement of the Reflecting Telescope, the first object has always been to increase the magnifying power and light by the construction of as large a mirror as possible; and to this point Lord Rosse’s attention was directed as early as 1828, the field of operation being at his lordship’s seat, Birr Castle at Parsonstown, about fifty miles west of Dublin. For this high branch of scientific inquiry Lord Rosse was well fitted by a rare combination of “talent to devise, patience to bear disappointment, perseverance, profound mathematical knowledge, mechanical skill, and uninterrupted leisure from other pursuits;”[26] all these, however, would not have been sufficient, had not a great command of money been added; the gigantic telescope we are about to describe having cost certainly not less than twelve thousand pounds.

Lord Rosse ground and polished specula fifteen inches, two feet,
and three feet in diameter before he commenced the colossal
instrument. It is impossible here to detail the admirable
contrivances and processes by which he prepared himself for this
great work. He first ascertained the most useful combination of
metals for specula, both in whiteness, porosity, and hardness,
to be copper and tin. Of this compound the reflector was cast in
pieces, which were fixed on a bed of zinc and copper,--a species
of brass which expanded in the same degree by heat as the pieces
of the speculum themselves. They were ground as one body to a true
surface, and then polished by machinery moved by a steam-engine.
The peculiarities of this mechanism were entirely Lord Rosse’s
invention, and the result of close calculation and observation:
they were chiefly, placing the speculum with the face upward,
regulating the temperature by having it immersed in water, usually
at 55° Fahr., and regulating the pressure and velocity. This was
found to work a perfect spherical figure in large surfaces with
a degree of precision unattainable by the hand; the polisher, by
working above and upon the face of the speculum, being enabled
to examine the operation as it proceeded without removing the
speculum, which, when a ton weight, is no easy matter.

The contrivance for doing this is very beautiful. The machine is
placed in a room at the bottom of a high tower, in the successive
floors of which trap-doors can be opened. A mast is elevated on the
top of the tower, so that its summit is about ninety feet _above_
the speculum. A dial-plate is attached to the top of the mast, and
a small plane speculum and eye-piece, with proper adjustments,
are so placed that the combination becomes a Newtonian telescope,
and the dial-plate the object. The last and most important part
of the process of working the speculum, is to give it a _true
parabolic figure_, that is, such a figure that each portion of it
should reflect the incident ray to the same focus. Lord Rosse’s
operations for this purpose consist--1st, of a stroke of the first
eccentric, which carries the polisher along _one-third_ of the
diameter of the speculum; 2d, a transverse stroke twenty-one times
slower, and equal to 0·27 of the same diameter, measured on the
edge of the tank, or 1·7 beyond the centre of the polisher; 3d, a
rotation of the speculum performed in the same time as thirty-seven
of the first strokes; and 4th, a rotation of the polisher in the
same direction about sixteen times slower. If these rules are
attended to, the machine will give the true parabolic figure to the
speculum, whether it be _six inches_ or _three feet in diameter_.
In the three-feet speculum, the figure is so true with the whole
aperture, that it is thrown out of focus by a motion of less
than the _thirtieth of an inch_, “and even with a single lens of
one-eighth of an inch focus, giving a power of 2592, the dots on a
watch-dial are still in some degree defined.”

Thus was executed the three-feet speculum for the twenty-six-feet telescope placed upon the lawn at Parsonstown, which, in 1840, showed with powers up to 1000 and even 1600; and which resolved nebulæ into stars, and destroyed that symmetry of form in globular nebulæ upon which was founded the hypothesis of the gradual condensation of nebulous matter into suns and planets.[27]

Scarcely was this instrument out of Lord Rosse’s hands, when he resolved to attempt by the same processes to construct another reflector, with a speculum _six feet_ in diameter and _fifty feet long_! and this magnificent instrument was completed early in 1845. The focal length of the speculum is fifty-four feet. It weighs four tons, and, with its supports, is seven times as heavy as the four-feet speculum of Sir William Herschel. The speculum is placed in one of the sides of a cubical wooden box, about eight feet wide, and to the opposite end of this box is fastened the tube, which is made of deal staves an inch thick, hooped with iron clamp-rings, like a huge cask. It carries at its upper end, and in the axis of the tube, a small oval speculum, six inches in its lesser diameter.

The tube is about 50 feet long and 8 feet in diameter in the middle, and furnished with diaphragms 6½ feet in aperture. The late Dean of Ely walked through the tube with an umbrella up.

The telescope is established between two lofty castellated piers 60 feet high, and is raised to different altitudes by a strong chain-cable attached to the top of the tube. This cable passes over a pulley on a frame down to a windlass on the ground, which is wrought by two assistants. To the frame are attached chain-guys fastened to the counterweights; and the telescope is balanced by these counterweights suspended by chains, which are fixed to the sides of the tube and pass over large iron pulleys. The immense mass of matter weighs about twelve tons.

On the eastern pier is a strong semicircle of cast-iron, with which the telescope is connected by a racked bar, with friction-rollers attached to the tube by wheelwork, so that by means of a handle near the eye-piece, the observer can move the telescope along the bar on either side of the meridian, to the distance of an hour for an equatorial star.

On the western pier are stairs and galleries. The observing gallery is moved along a railway by means of wheels and a winch; and the mechanism for raising the galleries to various altitudes is very ingenious. Sometimes the galleries, filled with observers, are suspended midway between the two piers, over a chasm sixty feet deep.

An excellent description of this immense Telescope at Birr Castle will be found in Mr. Weld’s volume of _Vacation Rambles_.

Sir David Brewster thus eloquently sketches the powers of the telescope at the close of his able description of the instrument, which we have in part quoted from his _Life of Sir Isaac Newton_.

We have, in the mornings, walked again and again, and ever with
new delight, along its mystic tube, and at midnight, with its
distinguished architect, pondered over the marvellous sights which
it dis-closes,--the satellites and belts and rings of Saturn,--the
old and new ring, which is advancing with its crest of waters to
the body of the planet,--the rocks, and mountains, and valleys, and
extinct volcanoes of the moon,--the crescent of Venus, with its
mountainous outline,--the systems of double and triple stars,--the
nebulæ and starry clusters of every variety of shape,--and those
spiral nebular formations which baffle human comprehension, and
constitute the greatest achievement in modern discovery.

The Astronomer Royal, Mr. Airy, alludes to the impression made by the enormous light of the telescope,--partly by the modifications produced in the appearance of nebulæ already figured, partly by the great number of stars seen at a distance from the Milky Way, and partly from the prodigious brilliancy of Saturn. The account given by another astronomer of the appearance of Jupiter was that it resembled a coach-lamp in the telescope; and this well expresses the blaze of light which is seen in the instrument.

The Rev. Dr. Scoresby thus records the results of his visits:

The range opened to us by the great telescope at Birr Castle is
best, perhaps, apprehended by the now usual measurement--not of
distances in miles, or millions of miles, or diameters of the
earth’s orbit, but--of the progress of light in free space. The
determination within, no doubt, a small proportion of error of
the parallax of a considerable number of the fixed stars yields,
according to Mr. Peters, a space betwixt us and the fixed stars of
the smallest magnitude, the sixth, ordinarily visible to the naked
eye, of 130 years in the flight of light. This information enables
us, on the principles of _sounding the heavens_, suggested by Sir
W. Herschel, with the photometrical researches on the stars of Dr.
Wollaston and others, to carry the estimation of distances, and
that by no means on vague assumption, to the limits of space opened
out by the most effective telescopes. And from the guidance thus
afforded us as to the comparative power of the six feet speculum
in the penetration of space as already elucidated, we might fairly
assume the fact, that if any other telescope now in use could
follow the sun if removed to the remotest visible position, or
till its light would require 10,000 years to reach us, the grand
instrument at Parsonstown would follow it so far that from 20,000
to 25,000 years would be spent in the transmission of its light to
the earth. But in the cases of clusters of stars, and of nebulæ
exhibiting a mere speck of misty luminosity, from the combined
light of perhaps hundreds of thousands of suns, the _penetration_
into space, compared with the results of ordinary vision, must
be enormous; so that it would not be difficult to show the
_probability_ that a million of years, in flight of light, would
be requisite, in regard to the most distant, to trace the enormous
interval.

GIGANTIC TELESCOPES PROPOSED.

Hooke is said to have proposed the use of Telescopes having a length of upwards of 10,000 feet (or nearly two miles), in order to see animals in the moon! an extravagant expectation which Auzout considered it necessary to refute. The Capuchin monk Schyrle von Rheita, who was well versed in optics, had already spoken of the speedy practicability of constructing telescopes that should magnify 4000 times, by means of which the lunar mountains might be accurately laid down.

Optical instruments of such enormous focal lengths remind us of the Arabian contrivances of measurement: quadrants with a radius of about 190 feet, upon whose graduated limb the image of the sun was received as in the gnomon, through a small round aperture. Such a quadrant was erected at Samarcand, probably constructed after the model of the older sextants of Alchokandi, which were about sixty feet in height.

LATE INVENTION OF OPTICAL INSTRUMENTS.

A writer in the _North-British Review_, No. 50, considers it strange that a variety of facts which must have presented themselves to the most careless observer should not have led to the earlier construction of Optical Instruments. The ancients, doubtless, must have formed metallic articles with concave surfaces, in which the observer could not fail to see himself magnified; and if the radius of the concavity exceeded twelve inches, twice the focal distance of his eye, he had in his hands an extempore reflecting telescope of the Newtonian form, in which the concave metal was the speculum, and his eye the eye-glass, and which would magnify and bring near him the image of objects nearly behind him. Through the spherical drops of water suspended before his eye, an attentive observer might have seen magnified some minute body placed accidentally in its anterior focus; and in the eyes of fishes and quadrupeds which he used for his food, he might have seen, and might have extracted, the beautiful lenses which they contain, and which he could not fail to regard as the principal agents in the vision of the animals to which they belonged. Curiosity might have prompted him to look through these remarkable lenses or spheres; and had he placed the lens of the smallest minnow, or that of the bird, the sheep, or the ox, in or before a circular aperture, he would have produced a microscope or microscopes of excellent quality and different magnifying powers. No such observations seem, however, to have been made; and even after the invention of glass, and its conversion into globular vessels, through which, when filled with any fluid, objects are magnified, the microscope remained undiscovered.

A TRIAD OF CONTEMPORARY ASTRONOMERS.

It is a remarkable fact in the history of astronomy (says Sir David Brewster), that three of its most distinguished professors were contemporaries. Galileo was the contemporary of Tycho during thirty-seven years, and of Kepler during the fifty-nine years of his life. Galileo was born seven years before Kepler, and survived him nearly the same time. We have not learned that the intellectual triumvirate of the age enjoyed any opportunity for mutual congratulation. What a privilege would it have been to have contrasted the aristocratic dignity of Tycho with the reckless ease of Kepler, and the manly and impetuous mien of the Italian sage!--_Brewster’s Life of Newton._

A PEASANT ASTRONOMER.

At about the same time that Goodricke discovered the variation of the remarkable periodical star Algol, or β Persei, one Palitzch, a farmer of Prolitz, near Dresden,--a peasant by station, an astronomer by nature,--from his familiar acquaintance with the aspect of the heavens, was led to notice, among so many thousand stars, Algol, as distinguished from the rest by its variation, and ascertained its period. The same Palitzch was also the first to re-discover the predicted comet of Halley in 1759, which he saw nearly a month before any of the astronomers, who, armed with their telescopes, were anxiously watching its return. These anecdotes carry us back to the era of the Chaldean shepherds.--_Sir John Herschel’s Outlines._

SHIRBURN-CASTLE OBSERVATORY.

Lord Macclesfield, the eminent mathematician, who was twelve years President of the Royal Society, built at his seat, Shirburn Castle in Oxfordshire, an Observatory, about 1739. It stood 100 yards south from the castle-gate, and consisted of a bed-chamber, a room for the transit, and the third for a mural quadrant. In the possession of the Royal Astronomical Society is a curious print representing two of Lord Macclesfield’s servants taking observations in the Shirburn observatory; they are Thomas Phelps, aged 82, who, from being a stable-boy to Lord-Chancellor Macclesfield, rose by his merit and genius to be appointed observer. His companion is John Bartlett, originally a shepherd, in which station he, by books and observation, acquired such a knowledge in computation, and of the heavenly bodies, as to induce Lord Macclesfield to appoint him assistant-observer in his observatory. Phelps was the person who, on December 23d, 1743, discovered the great comet, and made the first observation of it; an account of which is entered in the _Philosophical Transactions_, but not the name of the observer.

LACAILLE’S OBSERVATORY.

Lacaille, who made more observations than all his contemporaries put together, and whose researches will have the highest value as long as astronomy is cultivated, had an observatory at the Collège Mazarin, part of which is now the Palace of the Institute, at Paris.

For a long time it had been without observer or instruments;
under Napoleon’s reign it was demolished. Lacaille never used
to illuminate the wires of his instruments. The inner part of
his observatory was painted black; he admitted only the faintest
light, to enable him to see his pendulum and his paper: his left
eye was devoted to the service of looking to the pendulum, whilst
his right eye was kept shut. The latter was only employed to look
to the telescope, and during the time of observation never opened
but for this purpose. Thus the faintest light made him distinguish
the wires, and he very seldom felt the necessity of illuminating
them. Part of these blackened walls were visible long after the
demolition of the observatory, which took place somewhat about
1811.--_Professor Mohl._

NICETY REQUIRED IN ASTRONOMICAL CALCULATIONS.

In the _Edinburgh Review_, 1850, we find the following illustrations of the enormous propagation of minute errors:

The rod used in measuring a base-line is commonly about ten
feet long; and the astronomer may be said truly to apply that
very rod to mete the distance of the stars. An error in placing
a fine dot which fixes the length of the rod, amounting to
one-five-thousandth of an inch (the thickness of a single silken
fibre), will amount to an error of 70 feet in the earth’s diameter,
of 316 miles in the sun’s distance, and to 65,200,000 miles in
that of the nearest fixed star. Secondly, as the astronomer in his
observatory has nothing further to do with ascertaining lengths or
distances, except by calculation, his whole skill and artifice are
exhausted in the measurement of angles; for by these alone spaces
inaccessible can be compared. Happily, a ray of light is straight:
were it not so (in celestial spaces at least), there would be an
end of our astronomy. Now an angle of a second (3600 to a degree)
is a subtle thing. It has an apparent breadth utterly invisible to
the unassisted eye, unless accompanied with so intense a splendour
(_e. g._ in the case of a fixed star) as actually to raise by its
effect on the nerve of sight a spurious image having a sensible
breadth. A silkworm’s fibre, such as we have mentioned above,
subtends an angle of a second at 3½ feet distance; a cricket-ball,
2½ inches diameter, must be removed, in order to subtend a second,
to 43,000 feet, or about 8 miles, where it would be utterly
invisible to the sharpest sight aided even by a telescope of some
power. Yet it is on the measure of one single second that the
ascertainment of a sensible parallax in any fixed star depends;
and an error of one-thousandth of that amount (a quantity still
unmeasurable by the most perfect of our instruments) would place
the star too far or too near by 200,000,000,000 miles; a space
which light requires 118 days to travel.

CAN STARS BE SEEN BY DAYLIGHT?

Aristotle maintains that Stars may occasionally be seen in the Daylight, from caverns and cisterns, as through tubes. Pliny alludes to the same circumstance, and mentions that stars have been most distinctly recognised during solar eclipses. Sir John Herschel has heard it stated by a celebrated optician, that his attention was first drawn to astronomy by the regular appearance, at a certain hour, for several successive days, of a considerable star through the shaft of a chimney. The chimney-sweepers who have been questioned upon this subject agree tolerably well in stating that “they have never seen stars by day, but that when observed at night through deep shafts, the sky appeared quite near, and the stars larger.” Saussure states that stars have been seen with the naked eye in broad daylight, on the declivity of Mont Blanc, at an elevation of 12,757 feet, as he was assured by several of the alpine guides. The observer must be placed entirely in the shade, and have a thick and massive shade above his head, else the stronger light of the air will disperse the faint image of the stars; these conditions resembling those presented by the cisterns of the ancients, and the chimneys above referred to. Humboldt, however, questions the accuracy of these evidences, adding that in the Cordilleras of Mexico, Quito, and Peru, at elevations of 15,000 or 16,000 feet above the sea-level, he never could distinguish stars by daylight. Yet, under the ethereally pure sky of Cumana, in the plains near the sea-shore, Humboldt has frequently been able, after observing an eclipse of Jupiter’s satellites, to find the planet again with the naked eye, and has most distinctly seen it when the sun’s disc was from 18° to 20° above the horizon.

LOST HEAT OF THE SUN.

By the nature of our atmosphere, we are protected from the influence of the full flood of solar heat. The absorption of caloric by the air has been calculated at about one-fifth of the whole in passing through a column of 6000 feet, estimated near the earth’s surface. And we are enabled, knowing the increasing rarity of the upper regions of our gaseous envelope, in which the absorption is constantly diminishing, to prove that _about one-third of the solar heat is lost_ by vertical transmission through the whole extent of our atmosphere.--_J. D. Forbes, F.R.S._; _Bakerian Lecture_, 1842.

THE LONDON MONUMENT USED AS AN OBSERVATORY.

Soon after the completion of the Monument on Fish Street Hill, by Wren, in 1677, it was used by Hooke and other members of the Royal Society for astronomical purposes, but abandoned on account of the vibrations being too great for the nicety required in their observations. Hence arose _the report that the Monument was unsafe_, which has been revived in our time; “but,” says Elmes, “its scientific construction may bid defiance to the attacks of all but earthquakes for centuries to come.” This vibration in lofty columns is not uncommon. Captain Smythe, in his _Cycle of Celestial Objects_, tells us, that when taking observations on the summit of Pompey’s Pillar, near Alexandria, the mercury was sensibly affected by tremor, although the pillar is a solid.

Geology and Paleontology.

IDENTITY OF ASTRONOMY AND GEOLOGY.

While the Astronomer is studying the form and condition and structure of the planets, in so far as the eye and the telescope can aid him, the Geologist is investigating the form and condition and structure of the planet to which he belongs; and it is from the analogy of the earth’s structure, as thus ascertained, that the astronomer is enabled to form any rational conjecture respecting the nature and constitution of the other planetary bodies. Astronomy and Geology, therefore, constitute the same science--the science of material or inorganic nature.

When the astronomer first surveys the _concavity_ of the celestial vault, he finds it studded with luminous bodies differing in magnitude and lustre, some moving to the east and others to the west; while by far the greater number seem fixed in space; and it is the business of astronomers to assign to each of them its proper place and sphere, to determine their true distance from the earth, and to arrange them in systems throughout the regions of sidereal space.

In like manner, when the geologist surveys the _convexity_ of his own globe, he finds its solid covering composed of rocks and beds of all shapes and kinds, lying at every possible angle, occupying every possible position, and all of them, generally speaking, at the same distance from the earth’s centre. Every where we see what was deep brought into visible relation with what was superficial--what is old with what is new--what preceded life with what followed it.

Thus displayed on the surface of his globe, it becomes the business of the geologist to ascertain how these rocks came into their present places, to determine their different ages, and to fix the positions which they originally occupied, and consequently their different distances from the centre or the circumference of the earth. Raised from their original bed, the geologist must study the internal forces by which they were upheaved, and the agencies by which they were indurated; and when he finds that strata of every kind, from the primitive granite to the recent tertiary marine mud, have been thus brought within his reach, and prepared for his analysis, he reads their respective ages in the organic remains which they entomb; he studies the manner in which they have perished, and he counts the cycles of time and of life which they disclose.--_Abridged from the North-British Review_, No. 9.

THE GEOLOGY OF ENGLAND

is more interesting than that of other countries, because our island is in a great measure an epitome of the globe; and the observer who is familiar with our strata, and the fossil remains which they include, has not only prepared himself for similar inquiries in other countries, but is already, as it were, by anticipation, acquainted with what he is to find there.--_Transactions of the Geological Society._

PROBABLE ORIGIN OF THE ENGLISH CHANNEL.

The proposed construction of a submarine tunnel across the Straits of Dover has led M. Boué, For. Mem. Geol. Soc., to point out the probability that the English Channel has not been excavated by water-action only; but owes its origin to one of the lines of disturbance which have fissured this portion of the earth’s crust: and taking this view of the case, the fissure probably still exists, being merely filled with comparatively loose material, so as to prove a serious obstacle to any attempt made to drive through it a submarine tunnel.--_Proceedings of the Geological Society._

HOW BOULDERS ARE TRANSPORTED TO GREAT HEIGHTS.

Sir Roderick Murchison has shown that in Russia, when the Dwina is at its maximum height, and penetrates into the chinks of its limestone banks, when frozen and expanded it causes disruptions of the rock, the entanglement of stony fragments in the ice. In remarkable spring floods, the stream so expands that in bursting it throws up its icy fragments to 15 or 20 feet above the stream; and the waters subsiding, these lateral ice-heaps melt away, and leave upon the bank the rifled and angular blocks as evidence of the highest ice-mark. In Lapland, M. Böhtlingk assures us that he has found _large granitic boulders weighing several tons actually entangled and suspended, like birds’-nests, in the branches of pine-trees, at heights of 30 or 40 feet above the summer level of the stream_![28]

WHY SEA-SHELLS ARE FOUND AT GREAT HEIGHTS.

The action of subterranean forces in breaking through and elevating strata of sedimentary rocks,--of which the coast of Chili, in consequence of a great earthquake, furnishes an example,--leads to the assumption that the pelagic shells found by MM. Bonpland and Humboldt on the ridge of the Andes, at an elevation of more than 15,000 English feet, may have been conveyed to so extraordinary a position, not by a rising of the ocean, but by the agency of volcanic forces capable of elevating into ridges the softened crust of the earth.

SAND OF THE SEA AND DESERT.

That sand is an assemblage of small stones may be seen with the eye unarmed with art; yet how few are equally aware of the synonymous nature of the sand of the sea and of the land! Quartz, in the form of sand, covers almost entirely the bottom of the sea. It is spread over the banks of rivers, and forms vast plains, even at a very considerable elevation above the level of the sea, as the desert of Sahara in Africa, of Kobi in Asia, and many others. This quartz is produced, at least in part, from the disintegration of the primitive granite rocks. The currents of water carry it along, and when it is in very small, light, and rounded grains, even the wind transports it from one place to another. The hills are thus made to move like waves, and a deluge of sand frequently inundates the neighbouring countries:

“So where o’er wide Numidian wastes extend,
Sudden the impetuous hurricanes descend.”--_Addison’s Cato._

To illustrate the trite axiom, that nothing is lost, let us glance at the most important use of sand:

“Quartz in the form of sand,” observes Maltebrun, “furnishes, by
fusion, one of the most useful substances we have, namely glass,
which, being less hard than the crystals of quartz, can be made
equally transparent, and is equally serviceable to our wants and
to our pleasures. There it shines in walls of crystal in the
palaces of the great, reflecting the charms of a hundred assembled
beauties; there, in the hand of the philosopher, it discovers to us
the worlds that revolve above us in the immensity of space, and the
no less astonishing wonders that we tread beneath our feet.”

PEBBLES.

The various heights and situations at which Pebbles are found have led to many erroneous conclusions as to the period of changes of the earth’s surface. All the banks of rivers and lakes, and the shores of the sea, are covered with pebbles, rounded by the waves which have rolled them against each other, and which frequently seem to have brought them from a distance. There are also similar masses of pebbles found at very great elevations, to which the sea appears never to have been able to reach. We find them in the Alps at Valorsina, more than 6000 feet above the level of the sea; and on the mountain of Bon Homme, which is more than 1000 feet higher. There are some places little elevated above the level of the sea, which, like the famous plain of Crau, in Provence, are entirely paved with pebbles; while in Norway, near Quedlia, some mountains of considerable magnitude seem to be completely formed of them, and in such a manner that the largest pebbles occupy the summit, and their thickness and size diminish as you approach the base. We may include in the number of these confused and irregular heaps most of the depositions of matter brought by the river or sea, and left on the banks, and perhaps even those immense beds of sand which cover the centre of Asia and Africa. It is this circumstance which renders so uncertain the distinction, which it is nevertheless necessary to establish, between alluvial masses created before the commencement of history, and those which we see still forming under our own eyes.

A charming monograph, entitled “Thoughts on a Pebble,” full of playful sentiment and graceful fancy, has been written by the amiable Dr. Mantell, the geologist.

ELEVATION OF MOUNTAIN-CHAINS.

Professor Ansted, in his _Ancient World_, thus characterises this phenomenon:

These movements, described in a few words, were doubtless going
on for many thousands and tens of thousands of revolutions of our
planet. They were accompanied also by vast but slow changes of
other kinds. The expansive force employed in lifting up, by mighty
movements, the northern portion of the continent of Asia, found
partial vent; and from partial subaqueous fissures there were
poured out the tabular masses of basalt occurring in Central India;
while an extensive area of depression in the Indian Ocean, marked
by the coral islands of the Laccadives, the Maldives, the great
Chagos bank, and some others, were in the course of depression by a
counteracting movement.

Hitherto the processes of denudation and of elevation have been so far balanced as to preserve a pretty steady proportion of sea and dry land during geological ages; but if the internal temperature should be so far reduced as to be no longer capable of generating forces of expansion sufficient for this elevatory action, while the denuding forces should continue to act with unabated energy, the inevitable result would be, that every mountain-top would be in time brought low. No earthly barrier could declare to the ocean that there its proud waves should be stayed. Nothing would stop its ravages till all dry land should be laid prostrate, to form the bed over which it would continue to roll an uninterrupted sea.

THE CHALK FORMATION.

Mr. Horner, F.R.S., among other things in his researches in the Delta, considers it extremely probable that every particle of Chalk in the world has at some period been circulating in the system of a living animal.

WEAR OF BUILDING-STONES.

Professor Henry, in an account of testing the marbles used in building the Capitol at Washington, states that every flash of lightning produces an appreciable amount of nitric acid, which, diffused in rain-water, acts on the carbonate of lime; and from specimens subjected to actual freezing, it was found that in ten thousand years one inch would be worn from the blocks by the action of frost.

In 1839, a report of the examination of Sandstones, Limestones,
and Oolites of Britain was made to the Government, with a view to
the selection of the best material for building the new Houses
of Parliament. For this purpose, 103 quarries were described, 96
buildings in England referred to, many chemical analyses of the
stones were given, and a great number of experiments related,
showing, among other points, the cohesive power of each stone,
and the amount of disintegration apparent, when subjected to
Brard’s process. The magnesian limestone, or dolomite of Bolsover
Moor, was recommended, and finally adopted for the Houses; but
the selection does not appear to have been so successful as might
have been expected from the skill and labour of the investigation.
It may be interesting to add, that the publication of the above
Report (for which see _Year-Book of Facts_, 1840, pp. 78-80)
occasioned Mr. John Mallcott to remark in the _Times_ journal,
“that all stone made use of in the immediate neighbourhood of its
own quarries is more likely to endure that atmosphere than if it
be removed therefrom, though only thirty or forty miles:” and the
lapse of comparatively few years has proved the soundness of this
observation.[29]

PHENOMENA OF GLACIERS ILLUSTRATED.

Professor Tyndall, being desirous of investigating some of the phenomena presented by the large masses of mountain-ice,--those frozen rivers called Glaciers,--devised the plan of sending a destructive agent into the midst of a mass of ice, so as to break down its structure in the interior, in order to see if this method would reveal any thing of its internal constitution. Taking advantage of the bright weather of 1857, he concentrated a beam of sunlight by a condensing lens, so as to form the focus of the sun’s rays in the midst of a mass of ice. A portion of the ice was melted, but the surrounding parts shone out as brilliant stars, produced by the reflection of the faces of the crystalline structure. On examining these brilliant portions with a lens, Professor Tyndall discovered that the structure of the ice had been broken down in symmetrical forms of great beauty, presenting minute stars, surrounded by six petals, forming a beautiful flower, the plane being always parallel to the plane of congelation of the ice. He then prepared a piece of ice, by making both its surfaces smooth and parallel to each other. He concentrated in the centre of the ice the rays of heat from the electric light; and then, placing the piece of ice in the electric microscope, the disc revealed these beautiful ice-flowers.

A mass of ice was crushed into fragments; the small fragments were then placed in a cup of wood; a hollow wooden die, somewhat smaller than the cup, was then pressed into the cup of ice-fragments by the pressure of a hydraulic press, and the ice-fragments were immediately united into a compact cup of nearly transparent ice. This pressure of fragments of ice into a solid mass explains the formation of the glaciers and their origin. They are composed of particles of ice or snow; as they descend the sides of the mountain, the pressure of the snow becomes sufficiently great to compress the mass into solid ice, until it becomes so great as to form the beautiful blue ice of the glaciers. This compression, however, will not form the solid mass unless the temperature of the ice be near that of freezing water. To prove this, the lecturer cooled a mass of ice, by wrapping it in a piece of tinfoil and exposing it for some time to a bath of the ethereal solution of solidified carbonic-acid gas, the coldest freezing mixture known. This cooled mass of ice was crushed to fragments, and submitted to the same pressure which the other fragments had been exposed to without cohering in the slightest degree.--_Lecture at the Royal Institution_, 1858.

ANTIQUITY OF GLACIERS.

The importance of glacier agency in the past as well as the present condition of the earth, is undoubtedly very great. One of our most accomplished and ingenious geologists has, indeed, carried back the existence of Glaciers to an epoch of dim antiquity, even in the reckoning of that science whose chronology is counted in millions of years. Professor Ramsay has shown ground for believing that in the fragments of rock that go to make up the conglomerates of the Permian strata, intermediate between the Old and the New Red Sandstone, there is still preserved a record of the action of ice, either in glaciers or floating icebergs, before those strata were consolidated.--_Saturday Review_, No. 142.

FLOW OF THE MER DE GLACE.

Michel Devouasson of Chamouni fell into a crevasse on the Glacier of Talefre, a feeder of the Mer de Glace, on the 29th of July 1836, and after a severe struggle extricated himself, leaving his knapsack below. The identical knapsack reappeared in July 1846, at a spot on the surface of the glacier _four thousand three hundred_ feet from the place where it was lost, as ascertained by Professor Forbes, who himself collected the fragments; thus indicating the rate of flow of the icy river in the intervening ten years.--_Quarterly Review_, No. 202.

THE ALLUVIAL LAND OF EGYPT: ANCIENT POTTERY.

Mr. L. Horner, in his recent researches near Cairo, with the view of throwing light upon the geological history of the alluvial land of Egypt, obtained from the lowest part of the boring of the sediment at the colossal statue of Rameses, at a depth of thirty-nine feet, this curious relic of the ancient world; the boring instrument bringing up a fragment of pottery about an inch square and a quarter of an inch in thickness--the two surfaces being of a brick-red colour, the interior dark gray. According to Mr. Horner’s deductions, this fragment, having been found at a depth of 39 feet (if there be no fallacy in his reasoning), must be held to be a record of the existence of man 13,375 years before A.D. 1858, reckoning by the calculated rate of increase of three inches and a half of alluvium in a century--11,517 years before the Christian era, and 7625 before the beginning assigned by Lepsius to the reign of Menos, the founder of Memphis. Moreover it proves in his opinion, that man had already reached a state of civilisation, so far at least as to be able to fashion clay into vessels, and to know how to harden it by the action of strong heat. This calculation is supported by the Chevalier Bunsen, who is of opinion that the first epochs of the history of the human race demand at the least a period of 20,000 years before our era as a fair starting-point in the earth’s history.--_Proceedings of Royal Soc._, 1858.

Upon this theory, a Correspondent, “An Old Indigo-Planter,” writes
to the _Athenæum_, No. 1509, the following suggestive note: “Having
lived many years on the banks of the Ganges, I have seen the stream
encroach on a village, undermining the bank where it stood, and
deposit, as a natural result, bricks, pottery, &c. in the bottom
of the stream. On one occasion, I am certain that the depth of
the stream where the bank was breaking was above 40 feet; yet in
three years the current of the river drifted so much, that a fresh
deposit of soil took place over the _débris_ of the village, and
the earth was raised to a level with the old bank. Now had our
traveller then obtained a bit of pottery from where it had lain for
only three years, could he reasonably draw the inference that it
had been made 13,000 years before?”

SUCCESSIVE CHANGES OF THE TEMPLE OF SERAPIS.

The Temple of Serapis at Puzzuoli, near Naples, is perhaps, of all the structures raised by the hands of man, the one which affords most instruction to a geologist. It has not only undergone a wonderful succession of changes in past time, but is still undergoing changes of condition. This edifice was exhumed in 1750 from the eastern shore of the Bay of Baiæ, consisting partly of strata containing marine shells with fragments of pottery and sculpture, and partly of volcanic matter of sub-aerial origin. Various theories were proposed in the last century to explain the perforations and attached animals observed on the middle zone of the three erect marble columns until recently standing; Goethe, among the rest, suggesting that a lagoon had once existed in the vestibule of the temple, filled during a temporary incursion of the sea with salt water, and that marine mollusca and annelids flourished for years in this lagoon at twelve feet or more above the sea-level.

This hypothesis was advanced at a time when almost any amount of fluctuation in the level of the sea was thought more probable than the slightest alteration in the level of the solid land. In 1807 the architect Niccolini observed that the pavement of the temple was dry, except when a violent south wind was blowing; whereas, on revisiting the temple fifteen years later, he found the pavement covered by salt water twice every day at high tide. From measurements made from 1822 to 1838, and thence to 1845, he inferred that the sea was gaining annually upon the floor of the temple at the rate of about one-third of an inch during the first period, and about three-fourths of an inch during the second. Mr. Smith of Jordan Hill, from his visits in 1819 and 1845, found an average rise of about an inch annually, which was in accordance with visits made by Mr. Babbage in 1828, and Professor James Forbes in 1826 and 1843. In 1852 Signor Scaecchi, at the request of Sir Charles Lyell, compared the depth of water on the pavement with its level taken by him in 1839, and found that it had gained only 4½ inches in thirteen years, and was not so deep as when MM. Niccolini and Smith measured it in 1845; from which he inferred that after 1845 the downward movement of the land had ceased, and before 1852 had been converted into an upward movement.

Arago and others maintained that the surface on which the temple stands has been depressed, has _remained under the sea, and has again been elevated_. Russager, however, contends that there is nothing in the vicinity of the temple, or in the temple itself, to justify this bold hypothesis. Every thing leads to the belief that the temple has remained unchanged in the position in which it was originally built; but that the sea rose, surrounded it to a height of at least twelve feet, and again retired; but the elevated position of the sea continued sufficiently long to admit of the animals boring the pillars. This view can even be proved historically; for Niccolini, in a memoir published in 1840, gives the heights of the level of the sea in the Bay of Naples for a period of 1900 years, and has with much acuteness proved his assertions historically. The correctness of Russager’s opinion, he states, can be demonstrated and reduced to figures by means of the dates collected by Niccolini.--See _Jameson’s Journal_, No. 58.

At the present time the floor is always covered with sea-water. On the whole, there is little doubt that the ground has sunk upwards of two feet during the last half-century. This gradual subsidence confirms in a remarkable manner Mr. Babbage’s conclusions--drawn from the calcareous incrustations formed by the hot springs on the walls of the building and from the ancient lines of the water-level at the base of the three columns--that the original subsidence was not sudden, but slow and by successive movements.

Sir Charles Lyell (who, in his _Principles of Geology_, has given a detailed account of the several upfillings of the temple) considers that when the mosaic pavement was re-constructed, the floor of the building must have stood about twelve feet above the level of 1838 (or about 11½ feet above the level of the sea), and that it had sunk about nineteen feet below that level before it was elevated by the eruption of Monte Nuovo.

We regret to add, that the columns of the temple are no longer in the position in which they served so many years as a species of self-registering hydrometer: the materials have been newly arranged, and thus has been torn as it were from history a page which can never be replaced.

THE GROTTO DEL CANE.

This “Dog Grotto” has been so much cited for its stratum of carbonic-acid gas covering the floor, that all geological travellers who visit Naples feel an interest in seeing the wonder.

This cavern was known to Pliny. It is continually exhaling from its sides and floor volumes of steam mixed with carbonic-acid gas; but the latter, from its greater specific gravity, accumulates at the bottom, and flows over the step of the door. The upper part of the cave, therefore, is free from the gas, while the floor is completely covered by it. Addison, on his visit, made some interesting experiments. He found that a pistol could not be fired at the bottom; and that on laying a train of gunpowder and igniting it on the outside of the cavern, the carbonic-acid gas “could not intercept the train of fire when it once began flashing, nor hinder it from running to the very end.” He found that a viper was nine minutes in dying on the first trial, and ten minutes on the second; this increased vitality being, in his opinion, attributable to the stock of air which it had inhaled after the first trial. Dr. Daubeny found that phosphorus would continue lighted at about two feet above the bottom; that a sulphur-match went out in a few minutes above it, and a wax-taper at a still higher level. The keeper of the cavern has a dog, upon which he shows the effects of the gas, which, however, are quite as well, if not better, seen in a torch, a lighted candle, or a pistol.

“Unfortunately,” says Professor Silliman, “like some other grottoes, the enchantment of the ‘Dog Grotto’ disappears on a near view.” It is a little hole dug artificially in the side of a hill facing Lake Agnano: it is scarcely high enough for a person to stand upright in, and the aperture is closed by a door. Into this narrow cell a poor little dog is very unwillingly dragged and placed in a depression of the floor, where he is soon narcotised by the carbonic acid. The earth is warm to the hand, and the gas given out is very constant.

THE WATERS OF THE GLOBE GRADUALLY DECREASING.

This was maintained by M. Bory Saint Vincent, because the vast deserts of sand, mixed up with the salt and remains of marine animals, of which the surface of the globe is partly composed, were formerly inland seas, which have insensibly become dry. The Caspian, the Dead Sea, the Lake Baikal, &c. will become dry in their turn also, when their beds will be sandy deserts. The inland seas, whether they have only one outlet, as the Mediterranean, the Red Sea, the Baltic, &c., or whether they have several, as the Gulf of Mexico, the seas of O’Kotsk, of Japan, China, &c., will at some future time cease to communicate with the great basins of the ocean; they will become inland seas, true Caspians, and in due time will become likewise dry. On all sides the waters of rivers are seen to carry forward in their course the soil of the continent. Alluvial lands, deltas, banks of sand, form themselves near the coasts, and in the directions of the currents; madreporic animals lay the foundations of new lands; and while the straits become closed, while the depths of the sea fill up, the level of the sea, which it would seem natural should become higher, is sensibly lower. There is, therefore, an actual diminution of liquid matter.

THE SALT LAKE OF UTAH.

Lieutenant Gunnison, who has surveyed the great basin of the Salt Lake, states the water to be about one-third salt, which it yields on boiling. Its density is considerably greater than that of the Red Sea. One can hardly get the whole body below the surface: in a sitting position the head and shoulders will remain above the water, such is the strength of the brine; and on coming to the shore the body is covered with an incrustation of salt in fine crystals. During summer the lake throws on shore abundance of salt, while in winter it throws up Glauber salt plentifully. “The reason of this,” says Lieutenant Gunnison, “is left for the scientific to judge, and also what becomes of the enormous amount of fresh water poured into it by three or four large rivers,--Jordan, Bear, and Weber,--as there is no visible effect.”

FORCE OF RUNNING WATER.

It has been proved by experiment that the rapidity at the bottom of a stream is every where less than in any other part of it, and is greatest at the surface. Also, that in the middle of the stream the particles at the top move swifter than those at the sides. This slowness of the lowest and side currents is produced by friction; and when the rapidity is sufficiently great, the soil composing the sides and bottom gives way. If the water flows at the rate of three inches per second, it will tear up fine clay; six inches per second, fine sand; twelve inches per second, fine gravel; and three feet per second, stones the size of an egg.--_Sir Charles Lyell._

THE ARTESIAN WELL OF GRENELLE AT PARIS.

M. Peligot has ascertained that the Water of the Artesian Well of Grenelle contains not the least trace of air. Subterranean waters ought therefore to be _aerated_ before being used as aliment. Accordingly, at Grenelle, has been constructed a tower, from the top of which the water descends in innumerable threads, so as to present as much surface as possible to the air.

The boring of this Well by the Messrs. Mulot occupied seven years, one month, twenty-six days, to the depth of 1794½ English feet, or 194½ feet below the depth at which M. Elie de Beaumont foretold that water would be found. The sound, or borer, weighed 20,000 lb., and was treble the height of that of the dome of the Hôpital des Invalides at Paris. In May 1837, when the bore had reached 1246 feet 8 inches, the great chisel and 262 feet of rods fell to the bottom; and although these weighed five tons, M. Mulot tapped a screw on the head of the rods, and thus, connecting another length to them, after fifteen months’ labour, drew up the chisel. On another occasion, this chisel having been raised with great force, sank at one stroke 85 feet 3 inches into the chalk!

The depth of the Grenelle Well is nearly four times the height of
Strasburg Cathedral; more than six times the height of the Hôpital
des Invalides at Paris; more than four times the height of St.
Peter’s at Rome; nearly four times and a half the height of St.
Paul’s, and nine times the height of the Monument, London. Lastly,
suppose all the above edifices to be piled one upon each other,
from the base-line of the Well of Grenelle, and they would but
reach within 11½ feet of its surface.

MM. Elie de Beaumont and Arago never for a moment doubted the final
success of the work; their confidence being based on analogy, and
on a complete acquaintance with the geological structure of the
Paris basin, which is identical with that of the London basin
beneath the London clay.