232 Screntific Intelligence. 
Garbe* have published an interesting paper, in which they show 
by careful ae camp aveats that the reaction of the glass bulb fully 
accounts for the motion of the wheel; and their investigation 
caused Ss forces which act within the glass 
how 
de Pony ielle.+ In opposition it is oe that no distribution of 
statical electricity could maintain a constant motion, and furt 
Mr. Crook he cites an experiment of Mr. Cromwell F. Varley, with 
an apparatus so arranged that the electrical condition could 
tested with a delicate eg ata ; when not the slightest poke 
- electrical excitement could be de tected, aluhoogh the motion of 
e wheel was re er misiataiie 
whe convection theory has been recently advocated by F. 
Neesen,|| who describes a number of experiments which he thinks 
indicate that the wheel of the radiometer is moved by the gas 
vane of the enclo ook 2 glass walls, But the effects he obtains 
by plating ditine wheels unsymmetrically under the receiver of 
a mitentd pump, do not, as it seems to us, necessitate his expla- 
sn 
n currents and the peculiar motion of the radiometer is 
raitklogiy marked in many experiments which have been else where 
described, the one passing into the other at a certain degree of 
exhaustion. 
The emission or evaporation theory appears to have a 
with iy Osborne Reynolds. It was later maintained by Govi,** 
and recently it has formed the subject of an extended artiole—in 
The particles thus emitted may be either those of aeriform sub- 
stances adhering to or occluded by the solid materials of which 
in 
into the vaccuous s Leaving, peschie a questions in 
abeyance—as these pieyuialaty prefer, —there o doubt that the 
general order of the phenomena might be sioplelied if the assump- 
tions which the emission theory requires could be accepted; but 
on the other hand, the phenomena which % IIner adduces in sup- 
ort of his view, may be,—for the most part at least—fully as well 
explained by the more general mechanical theory of heat. Zoll- 
* + baibtiee de Chim. et de Phys., [V] xi, 45, Mai, 1877. 
Beiblatter, i, 170. gree rpacbge yf 329, § Pogg. Ann., clx, 143. 
[compar Zallner, Pogg. Ann., clx, 459. §[ Proc. Royal Soc., 1874, June 18. 
‘Ann., clx, 154, 296 and 459. ++ Comptes Rendus, Ixxxiii, 1. 
