TRANSACTIONS OF THE SECTIONS. 6 



solar spectrum undergo any displacement through the variation of gravity, in passing 

 from one latitude to another on the earth's surface. 



The operations at the Kew Observatory in terrestrial magnetism, and with the 

 pendulum apparatus recently erected there, will form the subject of a separate re- 

 port. In the former department the observations at Stonyhurst give, as the annual 

 ' secular decrease of dip for the mean epoch of 1861-69, 2''614 — a result not very dif- 

 ferent from that determined by General Sabine for London, viz. 2'-69. From the 

 same quarter we are informed that the annual increase of total force is -0030 British 

 unit. Although this requires observations continued over a longer period, it may 

 still be regarded as confirmatory of the fact that the total force is increasing. 



To Professor Tyndall's researches in radiant heat allusion has beeu already made. 

 From himself, however, we hope to receive a communication on his more recent 

 experiments, whereby he has been enabled entirely to cut oil' the luminous from 

 the calorific rays, and to produce not only combustion in an absolutely dark focus, 

 but also the incandescence of platinum by non-luminous rays. 



Among the experimental improvements in subjects kindred to this may be men- 

 tioned M. Marcus's new thermo-electric battery, an invention likely to render this 

 kind of battery far more generally serviceable than has hitherto been practicable. 

 Like many other inventions, this has not been without some kind of anticipation, in 

 a suggestion by Mr. Yv heatstone in ' The Philosophical Magazine ' as long ago as 

 1837. 



We should also notice a suggestion by M. Carlier, for dispensing with the covering 

 of the wire in electric coils. It is said that this has been carried out with such 

 success as to produce an increase rather than diminution of power. M. Richer also 

 suggests the use of sulphur plates instead of glass in electrical machines. Mr. Beale 

 has succeeded in using object-glasses for the microscope of much higher power 

 (V B in.) than heretofore ; and I must not omit to mention that an essential part of 

 the apparatus consists of a cap of the thinnest possible glass, manufactured only by 

 Mr. Chance of this city. 



From the Committee on Electrical Resistance we shall doubtless receive a fur- 

 ther report. But the gigantic experiment to which the whole subject has recently 

 been subjected — an experiment which, notwithstanding its present interruption, we 

 may still call a great scientific success — will doubtless give an additional interest 

 to anything that the members of the committee who accompanied the Atlantic 

 expedition may have to communicate. 



Side by side with these experimental researches, the mathematical theories of 

 molecular physics have been advanced in several directions. Professor Maxwell, in 

 this country, and M. Renard in France, have each contributed a nienioir on electro- 

 dynamics ; and the latter has deduced his fundamental formulae from the hypothesis 

 of a single fluid. M. Corun, by a happy application of M. Chasles's principle of 

 homographic planes, has deduced from MacCullagh's theory some propositions 

 relating to crystalline reflexion and refraction. These have the remarkable property 

 of being independent of the wave-surface, and therefore may be said to rest upon a 

 simpler frame of hypothesis. M. Corun is preparing some apparatus for the experi- 

 mental verification of his method. M. Boussinecq also has presented to the Academy 

 of Sciences a memoir on the theory of light, in which he has taken into account 

 terms of the second degree in the displacements. It would seem that the paper 

 contains generalizations comprising the theories of Fresnel, MacCullagh, and 

 Neumann. Lastly in this connexion may be mentioned the writings of M. Saint 

 Yenant on the vis viva of elastic systems, and his extension of the investigations of 

 Narvier and Poncelet on the resistance of elastic bars, rods, &c. 



In each of the main branches of pure mathematics, geometry and analysis, a 

 modern school has arisen. The former, originating with Carnot, Dupin, Poncelet, 

 and others, dates from the early part of the present century ; the latter, due in the 

 first instance to Cayley, Boole, and Sylvester, belongs wholly to the present gene- 

 ration. Both schools have this in common, that figures in the one case, and forms 

 in the other, are considered not merely as isolated individuals, but as associated 

 with other concomitant forms which characterize their various properties. 



In pure geometry we have the principle of projection, whereby any plane figure 

 is considered in connexion with all or any other plane figure lving on the same 



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