shape, the four longest sides being nearly at right angles to each other, while the ends were more irregular. Its medium length was 6 feet; its breadth, 5 feet; and its thickness, 2 feet. Consequently its weight was about eight tons. It was determined to raise it out of its bed; and when this was done, I was surprised to find the striæ more distinct upon the bottom than anywhere else. They were more minute upon the perpendicular sides than on any other part, though these sides were perhaps the most perfectly smoothed. But on all sides they were essentially parallel, although upon the top there were at least two sets, making a small angle with each other, as is common upon surfaces striated by the drift agency.

I had never met with a bowlder of this description. Its unique character awakened an ambition in the class to remove it entire. I doubted their ability to do this: but young men are strong, and in this case they were very skillful also; for although much of the way is ascending, they went through the work successfully, and without accident; and in a single day they planted the bowlder in front of the Wood's Cabinet on a slope, sustaining the lower end by portions of two large trap columns from Mount Tom, so that the visitor can look beneath and see the striæ there. It stands in the same position as originally, except that the ends are inverted. Deeply engraved upon one end are the words,-" The Class of 1857" that being the year when they graduate.

This rock is a fine-grained hard reddish sandstone, such as occurs on the west face of Mettawampe, (Mt. Toby,) a mountain lying nearly north of Amherst, ten miles distant, and from which the bowlder was undoubtedly derived.

How now shall we explain the parallel striation on four sides of this bowlder? Striated blocks I believe, have generally been regarded as having been frozen into an iceberg, or a glacier, which grated along the surface. But this explains the striæ only on one side. For if the bowlder should happen to have been frozen into a second iceberg, or glacier, how small a chance would there be, that it would be scratched in a parallel direction on a second side. Far less is the probability that a third side would have been striated in the same direction; and almost infinitely less the chance that a fourth side would have experienced a like dressing. Should a bowlder be frozen four times into a mass of ice, how almost certain that the stria would run in different directions. We must, therefore, give up the idea that this bowlder was scratched in the manner usually assigned. But suppose that when it started from Mettawampe on its southern journey, it were frozen into the bottom of an iceberg. As this grated over the rocky surface, it would soon be smoothed and striated: nor is it strange that in such a manner the erosion

and grooving should be deeper, and the edges less rounded, (as they are) than by what I suppose to have been the subsequent processes.

There is another way in which this striation of the bottom might have been accomplished. It might have been done while yet the bowlder was a part of the ledge from which it was broken. In that.case it must have been turned over after starting from its bed.

A third method may be suggested for this work. After the bowlder got mixed up with other fragments, and a strong vis a tergo, either aqueous or glacial, was pushing them all forward, so large a block as this might have pressed so heavily upon the surface as to be deeply furrowed.

That a strong force was exerted upon the bowlder to urge it forward, is obvious from a fact respecting the end of it, (A) lying towards the north (now the south end), as shown by the annexed outline. Both ends appear for the most part as if acted upon chiefly by water, being irregularly rounded and smoothed, but not furrowed, except in two places, a and b. Near the middle, the top, as may be seen, projects a foot or so, and on each side the surface is striated by lines running upwards, as if smaller bowlders had struck against it, and not being able to move it, were forced over it.

A

If a strong current were thus crowding detritus against and over the bowlder, its oblong form would keep its longer axis in the same direction as the stream. Hence the smaller fragments forced against and over it, would smooth the top and the sides in the same direction. They would press most heavily upon the top, and accordingly the striæ are much deeper there than upon the sides, though it should also be recollected that the edge of a stratum is usually harder than its face.

I impute the parallel striation of this bowlder, then, first to its great weight, which caused smaller fragments to slide over it more or less; and secondly, to its oblong form, which kept it nearly in the same position while advancing.

The only striæ on this bowlder not yet described, are a few faint ones running obliquely across the present north end, (the

south end as it lay originally). Most of these I presume are simply the marks of vehicles, which, for the whole spring, passed over this part of the bowlder, and I was surprised to find that they made so slight an impression. I think, however, that among these wagon tracks I can see one or two produced by some other agency; and it is not improbable that during its rough transportation, bowlders might have been forced over it in that direction.

I have regarded the detritus collected along the central part of Amherst, where this bowlder lay, as Modified Drift: that is, coarse drift that has been subsequently acted upon, and more or less rounded and sorted by water. Generally the fragments at this place are more rounded and of less size than we see in the coarse drift upon the neighboring hills, and yet the bowlders are considerably larger, though the one now described is much the largest I have seen in our modified drift.

As this bowlder seems to me to be of unusual interest, and is now placed permanently, through the energy and scientific zeal of the class of 1857, where geologists can examine it, I have thought this description might be acceptable to the readers of the Journal. At any rate, it has been the means of qualifying one College Class, as they wander over the world, to examine striated bowlders and ledges.

upon

SCIENTIFIC INTELLIGENCE.

I.

CHEMISTRY AND PHYSICS.

1. On the wave lengths of the most refrangible rays of light in the Interference Spectrum.-EISENLOHR has contributed a very interesting paper the wave lengths of the invisible rays, which he has determined by means of the diffraction spectrum, essentially in the manner employed by Schwerd. The author in the first place describes his method of projecting the phenomena of diffraction upon a screen. A ray of light is introduced horizontally into a dark room by means of a heliostat and allowed to fall upon a narrow vertical slit or other opening placed at a distance of one meter. From 4 to 12 meters behind this slit an achromatic objectglass of 3 meters focal length is placed in a round hole in a board, the plane of which is at right angles to the incident ray. Disks with lattices of different kinds may be fastened immediately in front of the object-glass; a white or transparent screen is placed at a proper distance behind the lens. The image of the slit must be distinctly projected upon this screen before the lattice is fastened in front of the object-glass. In this manner, spectra of extraordinary size and beauty are obtained, particularly when the openings are very narrow and numerous. All the phenomena of diffraction described by Schwerd in his classical work may in this way be represented so that they may be seen by a number of

persons at once. The author considers in the present paper only the phenomena which are seen with a lattice composed of numerous parallel openings. The one employed by him had 1440 parallel lines upon a plane glass 54mm. by 13mm. The spectrum obtained by this lattice could be projected upon a trough filled with a fluorescent liquid, upon paper impregnated with such a liquid, upon a ruler of uranium-glass or upon photographic paper. The spectrum as projected upon a common paper screen exhibited between the two spectra of the first order toward the centre and between the two lines H in the violet, an ill defined dark space. When fluorescent paper was made to receive the spectrum, this dark space became at once sharply defined. The spectrum was longer upon chinin-paper than upon the other fluorescent substances which the author tried, and he confined himself to this in his investigation. The author gives a mathematical investigation of the spectrum as produced by parallel openings, and then makes with the compasses upon the fluorescent paper the requisite measurements of the distances of the points where the first bright spectrum of the diffracted light commences. The wave length is then given by the formula e sin y, in which e represents the distance between two successive lattice-openings and the angle which the diffracted ray makes with the normal to the surface of the lattice. By placing a violet-colored glass over the opening near the heliostat, the most refrangible end of the spectrum became visible with still greater distinctness and exhibited the sharpest termination: even on common paper the spectrum could be seen and with exactly the same length. When the spectrum as thus produced was received upon a plate of porcelain, no trace of extension could be remarked; the spectrum terminated with the extreme visible rays. The author found as the results of his measurements the following wave lengths in fractions of a millimeter. Extreme visible red rays λ= 0.0007064.

Extreme visible violet rays 1. 0.0003956.

Most refrangible invisible rays 2 0.0003540.

Hence it appears that light from the extreme red to the extreme invisible ray embraces a complete octave.

With the view of confirming this result the author produced upon chinin-paper a spectrum by means of the same object-glass and a Munich flint glass prism of 45° at a distance of 7 meters. In this manner many of Fraunhofer's and Stokes's lines were seen with great distinctness. The distances of these lines were measured from the line B, and laid off as ordinates upon an axis of abscissas upon which the single distances of the ordinates are expressed by the difference of the corresponding wave lengths. In this manner the author obtained a curve which from the line I to the extreme invisible ray appears to follow the same law as the other portions of the spectrum. Eisenlohr has furthermore found that crown glass does not absorb the invisible rays in such a manner as to shorten the spectrum. This effect is produced by the low dispersive power of the glass for the invisible rays. This is shewn by the fact that a plate of crown glass placed so that the rays constituting the interference spectrum should pass through it before falling upon the chinin-paper does not produce any shortening of the spectrum. By piercing a hole in the screen upon which the spectrum was received where the invisible rays fell the

SECOND SERIES, VOL. XXII, NO. 66.-NOV., 1856.

author separated these and employed them for various experiments on polarization, double refraction and dispersion, which he promises to describe hereafter.-Pogg. Ann. xcviii, 353, June, 1856.

2. On the connection between the theorem of the equivalence of heat and work and the relations of permanent gases.-CLAUSIUS has published some critical remarks upon the paper of Hoppe which has been noticed in this Journal,* his object being mainly to shew that he himself had considered the subject from a different point of view and had arrived at essentially the same results as Hoppe. In a memoir "On a change in the form of the second principal theorem of the mechanical theory of heat," Clausius deduced the equation

in which denotes the heat communicated to a body during any change of state, W the external work performed, A the equivalent of heat for the unit of work, and U a quantity of which it may be assumed that it is perfectly determined by the initial and terminal state of the body. In the present notice the author deduces the results of Hoppe from this equation in the following simple manner. For the special case in which the state of the body is given by its temperature t and its volume v, U may be considered as a function of these two quantities. When the external work consists only in overcoming a pressure p which opposes the expansion, we have

W

and we obtain from the previous equation by differentiation,

d U
dt

=Sp dv,
+(+4.
1.p) dv.

(2) dQ= dt +

dM

dv

In applying this equation to the more special case of a permanent gas we may express the factors of dt and dv in another manner. The first of

d U
dt

these two factors is evidently nothing but the specific heat at a con

stant volume, and we write for it c. To express the second factor, the specific heat at a constant pressure, c' must be introduced. According to the laws of Gay Lussac and Mariotte, we have

in which a represents the inverse volume of the coefficient of expansion. Hence we have

The sum in the parenthesis [] represents the quantity c', and if we sub

dÚ
dt

tract from it the quantity c= we have

* Vol. xxi, p. 409.