Notices respecting New Books. 38 1 



embodying a thermoelectric law, the nature of which is thus 

 made accessible throughout an enormous range of tempera- 

 tures. 



This law is not fully contained in Tait's equation, as has 

 been already asserted ; nor did Prof. Tait claim that it would 

 be. I have spent much time in looking into this question, 

 but it does not seem worth while to adduce new results until 

 the calibration problem has been carried forward to a much 

 greater degree of nicety than was necessary in my geological 

 work. 



Phys. Lab., U.S. Geol. Survey, 

 Washington, D.C., U.S.A. 



XLIII. Notices respecting New Boohs. 



Cours de Physique, par J. Violle. Tome II., 2 me Partie : Optique 

 Geometrique. (Paris : G. Masson, 1892.) 



r PHIS treatise forms the first part of the Division " Optique " of a 

 -*~ Cours de Physique by the author, " Maitre de Conferences a 

 l'Ecole Normale," Paris ; the second part, now passing through the 

 press, being occupied with Physical Optics. To M. Violle, a pupil 

 of the late M. Verdet, in the posthumous editing of that able 

 teacher's lectures, the department of Electricity was assigned. 



This handsome octavo volume, of .356 pages with 276 finely 

 executed figures, contains a tolerably full account, with demon- 

 strations, of all that part of the science of Optics which is simply 

 dependent on the laws of reflexion and refraction of light at the 

 boundaries of ordinary homogeneous media, the usual experimental 

 verifications of those laws being described and made the foundation 

 of the volume. After their theory is explained, the manifold appli- 

 cations of plane mirrors are detailed, with full illustrations, from 

 the magic mirrors of Nostradamus and the late Prof. Pepper to 

 the more useful Sextants, Goniometers (that of Wollaston — date 

 unrecorded — being placed after Babinet's, of 1839), and Heliostats. 

 The subject of spherical mirrors introduces that of Aberrations 

 and Caustics ; and the Chapter (n.) concludes with a sketch of 

 the methods employed by Foucault in particular for making and 

 retouching parabolic mirrors. 



Chapter in. is divided into portions dealing severally with the 

 experimental proofs, and that through Permat's principle of quick- 

 est path, of the "Law of Sines:" the passage of light through 

 Plates and the Atmosphere, through Prisms and Lenses, spherical 

 and cylindric. The treatment is full and fairly complete, though 

 of course less so than in Mascart's larger work. Gauss's " Principal 

 Planes" and the theorems of Malus and Sturm are freely employed — 

 the latter being anticipated, some seventy pages before statement 

 and proof, in the discussion of the formation of the image of an 

 object under water, and the forms of the two sheets of the 

 " Caustic Surface." " Aberration " aud " Aplanetism " receive a 

 proportionate amount of treatment. 



