230 Notices respecting New Boohs. 



aether, by the effect of heat, and so to produce radiation; or 

 else electrical oscillations are set up in comparatively quiescent 

 atoms, not by heat, but by the impact of radiation from other 

 sources, or by some organic process set in play by living pro- 

 toplasm. 



It is thus I would seek to explain phosphorescence and 

 other direct production of light from cold sources. 



This direct production of light we have not yet learned 

 artificially to accomplish ; we can only heat bodies and trust 

 to their emitting light in some unknown manner as a 

 secondary result ; but the direct process has been learnt by 

 glowworms and Noctilucse, and it is for us ; I believe, one of 

 the problems of the immediate future. 



University College, Liverpool, 

 July 7, 1888. 



Postscript. — Since writing the above I have seen in the current 

 July number of Wiedemann's Annalen an article by Dr. Hertz, 

 wherein he establishes the existence and measures the length of 

 aether waves excited by coil discharges ; converting them into 

 stationary waves, not by reflexion of pulses transmitted along a 

 wire and reflected at its free end, as I have done, but by reflexion 

 of waves in free space at the surface of a conducting wall. 



My friend Mr. Chattock has also written to me about a recent 

 experiment exhibited to the Physical Society, I do not know by 

 whom, which shows that the same discharge as can excite aether 

 waves a kilometre long can excite air waves of one millimetre. 

 The whole subject of electrical radiation seems working itself out 

 splendidly. 



Cortina, Tyrol, July 24, 1888. 



XXII. Notices respecting New Books. 



Some Recent Works on Chemistry. 



Elementary Chemistry. By M. M. Pattison Muie, M.A., and 



Chakles Slatee, M.A., M.B. Cambridge University Press. 



1887. 

 Practical Chemistry, a course of laboratory work. By M. M. Pat- 



tison Muie, M.A., and Douglas Caenegie, B.A. Cambridge 



University Press. 1887. 

 CO many manuals, text-books, and elementary treatises on Che- 

 ^ mistry are now being issued by the teachers of the science that 

 it becomes almost invidious to select any of these works for notice 

 in these pages ; but Mr. Pattison Muir, who is Praelector in Che- 

 mistry of Gonville and Caius College, having for some time past 

 figured as a reformer in chemical teaching, we feel bound to call 

 attention to the two books above named. The first of these may 

 be described as the theoretical complement of the second work, 

 which is the laboratory guide for those who are undergoing instruc- 

 tion in the principles of science in accordance with the scheme laid 



