538 Notices respecting New Books. 



I will mention, in concluding, that the phenomenon of motion 

 in question is accompanied by a pretty luminous appearance, 

 which, however, is only visible in the dark. 



At the negative end of the tube, as far as the platinum wire 

 projects, a beautiful yellow fluorescent light appears in the glass, 

 and the same at the end of the mercurial column turned towards 

 the positive pole, which travels with it through the entire tube as 

 far as the positive bend, which, when the mercury reaches it, also 

 shines very brilliantly. The rest of the tube, excepting the 

 mercury, is filled with beautiful violet but unstratified light. It 

 is remarkable that as soon as the mercury has reached the posi- 

 tive bend, the yellow light on the negative leg loses its lustre 

 considerably, but soon acquires it again when the positive elec- 

 tricity is conducted away. Up to a certain degree its brilliance 

 increases, if the current, before entering the tube, has to strike 

 across a small layer of air. All tubes do not show the yellow 

 fluorescent light to the same extent, even if they are of the same 

 kind of glass *. 



LXX. Notices respecting New Booh. 



The Earth's Motion of Rotation, including the Theory of Precession 

 and Nutation. By C. H. H. Cheyne, M.A., of St. John's Col- 

 lege, Cambridge. (Pp. 52.) London and Cambridge : Macmil- 

 lan and Co. 1867. 

 fpHIS little treatise consists of two parts. In the first the author 

 ■*- shows that the motion of a body about its centre of gravity can be 

 determined by the following process, which is, in fact, an application 

 of Lagrange's theory of the Variation of Arbitrary Constants. If 

 the constants introduced into the equations for determination of the 

 motion when the body is acted on by no forces are treated as arbi- 

 trary functions, this solution can be adapted to the case in which 

 the body is acted on by "disturbing" forces. The author shows 

 that the differential coefficients of these functions with respect to 

 the time can be expressed in terms of a single function (V), and 

 that they exactly correspond to those used in the planetary theory 

 for determining the disturbed motion of a planet. This result, which 

 is perfectly general, having been obtained, the author proceeds in 



* According to Morren's statement (Ann. de Chim. et de Phys. ser. 4. 

 vol. iv. p. 365), uranium is present in all German glass, and the yellow 

 fluorescent light is produced by this uranium. The great intensity of this 

 light, which I have seen occur under very varied circumstances, rendered 

 me suspicious of this statement, and 1 therefore requested Dr. Stahlschmidt 

 to analyze the glass of the above tubes. This he has kindly done, and has 

 found that the glass in question, which is Thuringian, does not contain the 

 least trace of uranium ; but it does, in addition to some iron, contain a not 

 inconsiderable quantity of copper, although it is quite colourless. 



