Chemistry and Physics. 231 
SCIENTIFIC INTELLIGENCE, 
I. Puysics. 
hah 
have hee: during the past few months. Several of these 
nomena in question are liable to be modified by many adventitious 
circumstances. Five theories of the radiometer have found promi 
nent and weighty advocates. The first regards the motion of the 
instrument as a direct effect of radiation. ‘The second refers it to 
electrical action. The third to convection currents. The fourth 
to the emission of material particles from the vanes or the -_ 
of the instrument. Beg eise st finds in the apparatus simply a n 
heat engine, and sees in the motion a simple result of the differ- 
ence of Gatiparaahin of the pas wholly in accordance with the 
mere mechanical theory of hea 
n this motion was first ysis ered it seemed to. be a direct 
mochanioal effect of radiation, and there were not wanting ingenious 
speculations to show how the force exerted by the waves of the 
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whole tenor of his published’ papers have certainly justified, the 
common opinion that, until very recently, he regarded the phe- 
nomena—he had so admirably develo ae —as a direct effect of 
radiation, and not, as he now thinks, a secondary result depending 
on differences of temperature, which may be produced by radiation 
or by other means. Hence, several experimenters have labore 
to show that in the motion of the little wheel of the radiometer 
the reaction was exerted not against anything independent of the 
instrument, but a A ge the enclosing walls - Spoce ane — 
0 
slightly in the opposite direction. Soon after M. Salet} con- 
ructed a very ingenious apparatus ‘in wel this reaction was 
made to turn a mica disk; and very recently, M.M. Bertin et 
* Philosophical M agazine, Nov., 1876. 
+ Comptes Rendus, Nov. 20, 1876. 
