496 Notices respecting New Books. 



latter ; in this mauner the above-mentioned rotation follows with 

 the same necessity as the rotation of a wheel immersed in a 

 stream which Hows more strongly below than above. 



That this is the correct explanation is proved by observing 

 the phsenomena in the dark. An incomplete luminous circle is 

 then exhibited, which consists of two equal and opposite arches. 

 One of these arches is caused by the light which accompanies 

 the outflow of negative electricity. In consequence of the rapid 

 motion of the disc, the luminous red point appears as a con- 

 tinuous luminous arc. The opposite point, which at the same 

 time gives off positive electricity with a yellowish diffusive light, 

 originates the other arch in a similar manner ; the latter appear- 

 ing duller and wider than the former. The line which goes 

 through the middle of both arches and the centre of the needle 

 is not perpendicular to the disc, but obliquely inclined towards 

 its advancing particles. This line denotes the direction of maxr 

 imum attraction. 



The experiments succeed best when the disc has been tranquil 

 for some time previous, and the surrounding air not too highly 

 electrified by the rapid motion. That a violent motion of the 

 disc shoidd cause an irregular friction, and thereby an irregular 

 distribution of electricity over the sm'face, which in its turn 

 might affect the purity of the experiment, is easily conceivable. 

 The most suitable distance of the needle must be determined by 

 experiment. By observing these conditions the rotation may 

 be exhibited at any time without difficulty. The same phaeno- 

 menon can be exhibited with a cylindrical conductor, at the 

 extreme end of which the outflow of electricity by points is 

 effected. 



LXXI. Notices respecting New Books. 



An Introduction to the Atomic Theory . 5y Charles Daubeny, M.D., 

 F.R.S., 8;c., Professor of Chemistry and Botany in the University of 

 Oxford. 



CONSIDERING the vast importance of the doctrine of definite 

 proportions, very commonly termed, as in the present work, 

 the Atomic Theory, fewer publications directly and exclusively expla- 

 natory of the subject have appeared than might have been expected ; 

 and Dr. Daubeny has laid, not merely the tyro in chemistry under 

 obligation, but many well acquainted with the leading facts of che- 

 mical science, by presenting them with this publication. 



In his dedication of the work to the memory of John Dalton, the 

 author has "accurately described the doctrine in question as " a theory 

 with respect to the mode of combination between bodies, which stands 

 foremost among the discoveries of the present age for the universality 



