Mr. D. Kirkaldy has published some good practical remarks on the influence of repeated forging on the strength of wroughtiron.*

11. PHYSICS.

LIGHT.-The spectral analysis of the light of the stars has been followed up unremittingly by many observers. Amongst others, Father Secchi has published some generalizations: he divides the Stellar spectra into three types.

The first and most dominant type is that exhibited by white stars, such as Sirius. Their characteristic is a black band in the green-blue, and a second band in the violet.

Half the visible stars belong to this type. Two remarkable exceptions have been found, the stars y Cassiopeia and 8 Lyræ. These are perfectly complementary to the type, and instead of having a dark ray in the green, have a luminous band. Another modification of this type is presented by the constellation Orion (a excepted), which has no large bands, and in which the violet lines are very difficult to see. The second type consists of stars having coloured bands in the red and orange. The most remarkable and typical star of this class is Hercules, the spectrum of which has the appearance of a series of columns illuminated from one side; the stereoscopic effect of the convexity of these bands, due to the shading, is so surprising, that it cannot be beheld without astonishment. The third type consists of stars giving fine lines: it includes Arcturus, Capella, Pollux, &c., and also our own sun. The author says that the spectra of these stars perfectly resemble that of the sun, with fine lines in the same places. In these stars may be seen the principal solar rays, B, D, b, E, F, G, and a great many secondary rays.

As a proof of the existence of iron in the solar atmosphere, M. A. J. Angström has compared the solar spectrum with one formed by two iron electrodes, with a battery of 50 elements, and has found more than 460 rays corresponding to the lines of iron. Two observations which the author has made are of interest: one is the certain presence of manganese in the sun, proved by the coincidence of nearly thirty lines; and the other is the discovery of a new ray of hydrogen, situated nearly half way between G and H, and which M. Angström calls h.

An addition, which may prove important, has been made to our knowledge of the obscure subject of right- and left-handed polarization.

* Deutsche Industriezeitung,' No. 82. Organ für die Fortschritte des Eisenbahnwesens,' New Series, vol. iii., p. 178.

VOL. IV.

K

M. Gerney has discovered that a supersaturated solution of left-handed double tartrate of soda and ammonia does not crystallize in contact with a fragment of the same salt right-handed, and vice versa. From an inactive supersaturated solution of double racemate of soda and ammonia, a fragment of right-handed crystal determines only the precipitation of right-handed crystals; whilst a portion of the same liquid, in contact with a left-handed crystal, produces a deposit of the left-handed salt.

This supplies a simple means of separating at will from the double racemate of soda and ammonia, either of its two constituent salts.

M. Niepce de Saint Victor is perseveringly continuing his experiments on the photographic reproduction of colours. He has now succeeded in preparing a silver plate, on which all the colours, and even white and black, are capable of being impressed in the camera. His sixth memoir, which has just been communicated to the Academy of Sciences, contains several improvements in detail, principally with the view to obtain good blacks.

A memoir has been published by M. E. Reichert, on the different refractive powers of fluids, modified by their chemical composition. It contains the results of experiments on solutions. of common salt of different strengths, and the proportions of salt shown by optical means and by ordinary analysis agree very closely. An equally satisfactory result was obtained by solutions of sugar; but with alcohol and acetic acid, the differences in the refractive indices are only half as great.

The refraction- and dispersion- equivalents of chlorine, bromine, and iodine, have been examined by Dr. Gladstone, and by him communicated to the British Association. The refraction-equivalent of the substance is the product of its atomic weight with its specific refractive index-that is, its refractive index minus one, divided by its density. Its dispersion-equivalent is the difference between the refraction-equivalents as calculated for the two extreme lines of the spectrum, A and H.

From the determinations which Dr. Gladstone has made in conjunction with the Rev. T. P. Dale, it is seen that in each case the number for bromine lies between those for the other two. The refraction-equivalents are, for chlorine 9.8, for bromine 15.5, and iodine 24-2, and the dispersion equivalents are, for chlorine 0.5, bromine 13, and iodine 2.6.

HEAT. In experiments on radiant heat with the thermo-electric pile, M. P. Desains proposes the employment of a differential apparatus, consisting essentially of a single source of heat, of two thermoelectric piles, of a double-wire galvanometer, and finally of a rheostat. The apparatus is so arranged that the equilibrium, once obtained,

remains uniform, however the heat from the source varies; but if the smallest variation takes place in one of the radiations, the needle quits the zero point. The author has applied this apparatus to the examination of the absorption of heat by transparent gases, and finds that it gives very delicate and certain indications. This may be the case, but we do not see that the arrangement described by M. Desains is superior to Wheatstone's Bridge, the construction of which is peculiarly simple and easy, whilst the correct adjustment of a double wire differential galvanometer is a most difficult and uncertain operation.

The chemistry of the galvanic battery is a subject which would seem to have become almost exhausted. M. Favre has, however, contributed some important experiments, in which he has examined the amount of heat set in motion during galvanic decompositions or combinations. The conclusions at which he arrives are, that when a body is decomposed by the battery, the constituent elements, in separating, absorb a larger amount of heat than they disengage again in combining under ordinary circumstances. Thus, in the nascent state, bodies possess an excess of heat, which they give up on becoming modified to the ordinary state. The author's experi ments reveal another fact,-that secondary actions take place in the battery, accompanied by a disengagement of heat, which is not turned to account in the current, and therefore he says that electromagnetic machines cannot dispose of all the heat set in action in the battery.

M. de Gernez has investigated the subject of the disengagement of gases from their supersaturated solutions (of the sodawater type) and has discovered the following facts:-1st. Solid bodies, from which the gaseous bubbles are disengaged, lose their property after a certain time. 2nd. Prolonged soaking in water also removes this action from them, 3rd. Heat has the same action. 4th. Solid bodies, which have been in contact with air, have no action on supersaturated gaseous solutions. 5th. Air and gases provoke the disengagement of dissolved gas.

ELECTRICITY.--Electricity, although the youngest of the sciences, has already produced such marvellous results that some knowledge of its principles must, in future, form part of a liberal education. To impart this knowledge in a concise form has been the aim of Doctor Noad in his 'Text Book of Electricity.'* Of course, in a work of this sort, much originality is not expected, nor, indeed, would it be considered so desirable as a judicious selection, from acknowledged authorities, of those facts which form the groundwork of the science, and the truth of which has been

*The Student's Text-Book of Electricity. By Henry M. Noad, Ph.D., F.R.S., F.C.S., &c. London : Lockwood & Co.

universally admitted. This has been the course adopted by Doctor Noad in the present work, and the result is eminently satisfactory, including as it does, within the limits of a moderate-sized volume, all the information necessary to make the student acquainted with the present state of electrical science, as well as with the successive steps by which the knowledge has been obtained. Throughout the book extracts are freely inserted from such works as the report of the committee On the Construction of Submarine Cables,' the Cantor Lectures' of Mr. Fleeming Jenkin, and especially from the beautiful Experimental Researches" of Professor Faraday, with which every student of the science should be familiar. Of late years the practical applications of electricity have naturally received more attention than the theory of the science, and thus we find that, while very few important laws are of recent discovery, the branch relating to electric telegraphy, and more especially to submarine cables, has immensely advanced. Most of this advance is due, not so much to the discovery of new principles, as to the better application of those already discovered, and - almost the whole of the present system of testing may be said to be based upon two of these, viz. Ohm's law, and the law of derived circnits. The former is expressed by the formula

E

C = Ꭱ '

in which equation the current circulating, the electromotive force of the battery, and the resistance of the circuit, are connected together while the latter law is simply this, that if two paths are open for the electricity to travel by, the quantity circulating in each will be inversely as the resistances of the two branches. Wheatstone's bridge, or the electric balance, is one of the most ingenious and valuable applications of these laws; by its means the resistance of any circuit may be found in terms of a known resistance. A very clear description of this invention, and the principles on which it is based, is given in the Text Book.' Most of the information contained in the "Cantor Lectures," delivered by Mr. Fleeming Jenkin at the Society of Arts, will be found here in a condensed form, together with a full description of the improved galvanometers and electronometers invented by Sir William Thomson.

·

Turning from the scientific to the popular side of electricity, as exemplified by the induction coil, we find that here also progress has been chiefly in the direction of improved arrangement and manufacture. In Dr. Noad's treatise on this instrument,* much of the superiority of the modern coils is ascribed to the improved form By Henry M. Noad, Ph.D., F.R.S., F.C.S., &c. Second edition. London Churchill & Sons.

The Inductorium, or Induction Coil.

of contact-breaker introduced by Mr. Ladd, which allows the iron to attain to the maximum of magnetization before the current ceases. The static effects of the secondary current are also largely increased by the use of a condenser, as suggested by M. Fizeau, although the principle of its action is by no means clearly understood. Dr. Noad's Inductorium' gives a complete description and explanation of these instruments, together with a number of scientific and popular experiments which may be made with them. The Small Induction Coil' by J. H. is a description of the cheaper forms of coils which have lately become so popular. Without attempting an explanation of their principles, the author contents himself with showing their construction, and the purposes to which they may be applied; and, for the majority of purchasers of these instruments, his pamphlet will, we think, be found sufficient.

Some very valuable researches on the propagation of electricity in highly-rarefied elastic fluids, and on the stratifications of the electric light which accompany this propagation, have been published by M. A. De la Rive. The author has introduced a novel method of research, which appears capable of throwing considerable light on these obscure phenomena. He takes a large glass globe, furnished with four tubulures, having leather stuffingboxes traversed with metallic rods. Two of these are connected with a powerful Bunsen's battery, and the voltaic arc is produced between them. The other two rods are intended for the passage of an electric current from an induction coil. The voltaic arc is simply used as a source of heat to fill the exhausted globe with metallic vapours, and the phenomena which the author has investigated, are those produced by the passage of the induction current through this metallic vapour. The globe is first well exhausted, and then filled with nitrogen, which is rarefied to two or three millimetres' pressure, the induction-current is then turned on, and the Bunsen's battery is connected with the other rods, so as to produce a voltaic arc. In a few minutes the intensity of the induction-current augments considerably, and its colour alters according to the nature of the points between which the voltaic arc is formed. points of silver or zinc the light is of a decided blue colour; with copper, the tint is very deep green; with cadmium, apple-green; with magnesium, light green; and with aluminium, greenish white. In a second part of the paper the author studies the stratifications of the electric light, which he considers to be a phenomenon analogous to the production of sonorous waves. The third part is devoted to a discussion of particular phenomena

With

*A Popular Description of the Small Induction Coil, with a Variety of very Beautiful and Instructive Experiments.' By J. H. London: Varty & Cox.