treatise terminates with a series of tables of coefficients of friction, resistances to compression, tenacities, densities, &c. On the whole the work, though not free from faults, will give a real impulse to the cause of sound scientific education, and will be welcomed by both students and teachers. Mechanics is the mother of the physical sciences, and its study must precede that of any branch of physics. Any work which throws light upon its difficulties or which renders its study more attractive must be gratefully received, and regarded as a contribution to every branch of physical science. Prof. Bartlett's work promises to do good service as a carefully considered and well digested treatise upon one of the most difficult but most beautiful and useful of the sciences. 2. Darstellung der Farbenlehre und Optische Studien von H. W. Dové. Under this title Prof. Dové has published the second edition of an admirably clear and well written exposition of the theory of colors. The first edition of this work appeared in 1836, and has long been out of print. The author has now materially enlarged and in some measure recast it, and has added a series of original investigations upon various optical subjects of great value and interest. The work has the rare merit of being both popular and scientific. It is perfectly intelligible to any cultivated mind, while to the physicist by profession, and especially to the teacher of physics, it is full of suggestions which serve to illustrate and adorn familiar topics. The work commences with a historical introduction concerning the propagation of light and the earlier views of its nature. From this it passes to a brief consideration of the Newtonian theory and its final and complete overthrow, and then, after allusion to the now almost forgotten vagaries of Goethe, proceeds to the main portion of the subject. The author classifies colors according to their origin, into Prismatic Colors or colors produced by refrac tion, Colors of Interference, and Colors of Absorption. These three classes of colors differing in origin are then separately considered, and the application of the wave theory to their explanation pointed out. The papers collected under the name of Optical Studies relate to stereoscopic experiments and apparatus, to the polarization of light, and to experiments on subjective colors. The style of the work is lively and attractive, and we are glad to learn that an English translation of it may be expected.

3. Einleitung in die Höhere Optik von Dr. AUGUST BEER.-With this title Dr. Beer has published a treatise upon the wave theory of light, which is in all respects the most complete and satisfactory general view of that theory which has yet appeared. It is true that almost all the best recent treatises on physics employ the doctrine of undulations exclusively. General treatises on physics, however, are rarely suffi ciently full and explicit in the details of the application of theories, and usually confine themselves in a great measure at least to phenomena. The great work of Herschel on light has long been behind the age, while Radicke's Handbuch der Optik is obscure and not suited to the wants of the learner. Meantime memoirs and investigations without number have appeared, and the theory of waves may now be justly considered as almost perfect, and as entitled to rank with the theory of gravitation-in short to be considered as the second great physical gen eralization to which the human mind has arrived. A complete and

thorough elementary work on this branch of science has long been needed, and Dr. Beer's treatise deserves all praise. The work is divided into two parts. The first division, which is of a more elementary nature, treats of the principles of the wave theory for the simple case of isotropic media. The explanation of the attributes of color, intensity and polarization, is clearly set forth, and the fundamental laws of Catoptrics and Dioptrics are theoretically deduced. This portion of the work is in itself a very full treatise on descriptive Photics, though in a few particulars, as for example, upon the subject of circular polarization, more details would have been desirable. The chapter on interference is particularly worthy of notice, the subject being treated in the most general manner. This portion of the work closes with a description of Fessel's wave machine, for the representation of plane circular and elliptically polarized waves, as well as for the illustration of the interference of two rays. The second division treats of the analytical deduction of the laws of the motion of light, and of their experimental confirmation. The author obtains the equations for the condition of rest in the particles of the ether, and then those for a motion consisting of very small oscillations. The second chapter treats of isotropic media; the third of anisotropic media in general, and from this to the eleventh chapter inclusive the work is devoted to the phenomena of the motion of light in crystalline media. The treatise concludes with a description of the beautiful model of the wave surface in a biaxial crystal executed for Prof. Magnus, and the same we believe which was exhibited at the World's Fair in London, in 1852. In the body of the work many tables of optical constants are introduced, while the appendix gives the indices of refraction for a great number of substances as determined by different observers. This last table, however, as the indices do not refer either to definite rays in the spectrum, or to substances of definite constitution, is rather a blemish upon the work. Upon the whole, then, we regard Dr. Beer's treatise as one of the most truly important and valuable contributions to scientific literature which have appeared in recent times, and it is to be hoped that it may soon appear in an English dress, and thus become more generally ac cessible and useful.

4. Die Lehre von der Reibungselektricität von P. T. RIESS.-Prof. Riess is one of the few physicists who has devoted his energies exclusively to the subject of frictional electricity-a subject which, though at one time very popular, has of late years been but little studied. The treatise before us is of a truly German character. It embraces the whole subject of which it treats, and it exhausts that subject completely and systematically. The author divides his work into six sections. The first treats of the action of electrified bodies during their insulation. The second of the action of electrified bodies during their discharge. The third of the mechanism and effect of electric discharges. The fourth of the action of the connecting wire of a battery at a distance. The fifth of the excitement of electricity, and the sixth of atmospheric electricity. The author abstains entirely from theoretical considerations, and devotes his work exclusively to phenomena and their laws. The great mass of isolated experiments with which works on electricity usually abound serves only to confuse the subject, and Prof. Riess SECOND SERIES, Vol. XVII, No. 50.-March, 1854.

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has most judiciously confined himself as much as possible to general principles and to the statement of numerical results. English treatises on physics of late have done little else than re-echo the opinions of the illustrious Faraday upon this branch of science, and we owe this German physicist no inconsiderable debt of gratitude for his faithful exposition and dispassionate criticism of the labors of other experimenters. The results of Prof. Riess's own labors form no inconsiderable or unimportant part of his work, and we find here reproduced his papers on the torsion electrometer, on the development of heat in the connect. ing wire of the electric battery, on induced electrical currents, and upon many other interesting subjects. No treatise which has yet been published upon frictional electricity, at all compares with this in real extent, fullness and completeness, and it is no small part of its merit that it has been drawn wholly from the original sources, and has not been built up upon some other and older work as a foundation. Such works as this are needed in every branch of science; they demand for their production the clearest insight, the most dispassionate judg ment, and the most thorough and comprehensive knowledge. We earnestly hope that Prof. Riess' noble treatise may not long stand alone.

W. G.

5. On the Absolute Zero of the Perfect Gas Thermometer; being a Note to a Paper on the Mechanical Action of Heat; by W. J. MACQUORN RANKINE, Esq., (Abstract of a paper read to the Royal Society of Edinburgh, 4th January, 1853.)-Temperature being measured by the pressure of a perfect gas at constant density, the absolute zero of temperature is that point on the thermometric scale at which, if it were possible to maintain a perfect gas at so low a temperature, the pressure would be null.

As no gas is entirely devoid of cohesion, the immediate results of experiment give only approximations to the position of this absolute zero. These approximate positions approach nearer to the true posi tion as the gas is rarified.

The author having deduced the true position of the absolute zero from M. Regnault's experiments on atmospheric air and carbonic acid, soon after their publication, announced the result in the Edinburgh New Philosophical Journal for July, 1849, and in the Transactions of the Royal Society of Edinburgh, vol. xx.

The present paper gives the details of the method of determination which he adopted, and a copy of the diagram which he used. The following were the results arrived at:

The absolute zero of the perfect gas thermometer is

274° 6 Centigrade, or below the temperature of melting ice. 494° 28 Fahrenheit,

The coefficient of expansion of a perfect gas, in fractions of its volume at the temperature of melting ice, is consequently,―

6. Aridium; by CAMPBELL MORFIT and JAMES C. BOOTH, (Communicated for this Journal.)-Bahr (Jour. Prakt. Chem., Ix, 27,) having

stated his conviction, after recent and careful examination of the Norwegian Chromic Iron Ore, that Aridium, which Ullgren first announced as a new metal obtained by him from that mineral, is nothing more than oxyd of iron admixed with traces of phosphoric acid and oxyd of chrome; we take this opportunity of publishing that our experience is also adverse to the reality of its existence as a distinct element. Of numerous specimens of iron from various sources subjected to a searching method of analysis, (Chem. Gaz., 1853, p. 413,) not one was found to contain a particle of Aridium.

7. Note to J. D. Dana's Contributions to Chemical Mineralogy, p. 210; by the Author.-In writing the formulas on pages 218 to 220, fractions are used as preferable often to whole numbers. Thus, A1 Si, 1 Si, 1 Si, Al Si, are obviously more immediately appreciated and compared than the corresponding formulas, A14 Si3, A13 Si, A12 Si, Al Si. The old objection to fractions that atoms are indivisible is of no value. The ratios are correctly presented and these are all that analy sis affords. The actual number of molecules may be for the first, for example, Al40 Si30 or 124 Si18, etc., and Mr. T. S. Hunt has given good reason for believing that the molecules are in some such multiples. Hence Al Si3, taken as an expression of the absolute number of molecules is beyond doubt false; taken as a ratio simply, the fact is better exhibited by the fraction.

In the formulas, such as (R+R) Si or (3R3+3K) Si, the sum of the fractions is a unit; and in the first of these two formulas, they show that R3 is to as 1:1; in the second, as 3:2. These expressions or formulas of course come under the more general formula (R3, E) Si, in which R3 and are represented as mutually replaceable.

In the oxygen ratio of nepheline, on p. 220, 1:3:4, should be 1:3:41. It may be objected to the new view of the fundamental form of Tourmaline that the planes of it are less common on crystals than those of R (the R of authors). But it is true also in Calcite that -R is one of the most common forms, much more common than R. 8. On the Production of Crystalline Structure in Crystallized Powders, by Compression and Traction; by Sir DAVID BREWSTER, K.H., D.C.L., F.R.S., etc., (Trans. of the Roy. Soc. of Edinb., vol. xx, part 4; cited from the L., E. and D. Phil. Mag., vi, 260.)-The influence of com. pression and dilatation in producing the doubly refracting structure in solids of all kinds, whether crystallized or uncrystallized, which do not possess it, and in modifying that structure in all crystals which do possess it, has been long known; but with this class of phenomena, those which I am about to describe have no connexion whatever.

In the course of experiments on the double reflexion and polarization of light which I discovered in the chrysammates of potash and magnesia, murexide, and other crystals, I was surprised to find that these substances could be spread out upon glass by hard pressure, like grease or soft wax; and that in the case of chrysammate of potash and other bodies, when the powder could scarcely be distinguished from snuff, I obtained a transparent film, exhibiting the phenomena of double reflexion and polarization from its surface as perfectly as if I had been using a large crystal.

In subsequently repeating these experiments, and examining under polarized light the film thus produced by compression and traction, I was surprised to observe that the streaks and separate lines of the film, as well as the film itself, had regular axes of double refraction, as if they were regularly crystallized portions of the substance under examination. These streaks and capillary lines, which were often of extreme minuteness, did not appear to consist of insulated particles merely dragged into a line; but when the substance possessed the new property in perfection, the lines of polarized light were continuous, and the crystallographic as well as the optical axes of the particles were placed in that line. In other cases, where the experiment was less successful, the insulation of the particles was easily recognised, though. the general mass of them was crystallographically arranged.

In making these experiments, the natural crystalline powder, or the particles of the crushed crystal, may be placed either upon a polished glass surface or upon a piece of glass ground on one side. In those cases where the substance is soft, the polished surface is preferable; but when the powder is hard, and considerable pressure necessary, it is better to place it upon the ground surface of a piece of glass, as the particles are detained between its minute elevations, and submit more readily to the combined force of pressure and traction. When the powder is thus placed, I take a polished and elastic knife, and with its broad point I compress and drag the powder in a given direction till there is the appearance of a polished surface on the compressed substance. In general, I have used both the smooth and the rough glass, and have frequently obtained results with the one which were not given by the other.

If we now place the plate of glass in a polarizing microscope with the field dark, we shall find that the streaks and lines produced by traction have, in certain substances, regular neutral and depolarizing axes, as if they were prismatic crystals of the substance under examination. With the chrysammate of magnesia, a red powder with specks of yellow reflected light, the phenomena are peculiarly splendid; the natural colors of the substance, which vary greatly with the thickness of the streaks and films, being combined with the different tints which they polarize. As the crystals of this substance possess unusual reflexion, this property is displayed in the crystallized streaks produced by traction; and the superficial colors which they reflect vary with the azimuth which the plane of incidence forms with the plane passing through the axis of the prism.

The remarkable property which I have now described I have found, in a greater or a less degree, in the following crystals: