164 
POPULAR SCIENCE REVIEW. 
THE RADIOMETER. 
By W. H. STONE, M.B., F.R.C.P. 
LECTURER ON PHYSICS AT ST. THOMAS’S HOSPITAL. 
ITH the exception of the telephone, no discovery has for 
many years attracted so much public attention, both in 
scientific and in general circles, as the radiometer. Nor is this 
remarkable, if it be considered how perfectly novel and how 
to light. A new mine of knowledge seemed to have been 
opened, and it was matter of speculation as to what further 
treasures might thus be within our grasp. The crude facts of 
attraction, repulsion, and rotation were so unexpected, and yet 
so perfectly obvious, even to unpractised observers, that there is 
little cause for surprise at the warmth with which their expla- 
nation was attempted, and as little at the wildness and con- 
flicting character of many suggestions that were offered. Light, 
heat, electricity, evaporation and condensation, the molecular 
constitution of gases, and even less probable hypotheses, all 
offered specious and plausible modes of accounting for what 
was an objective reality past denying. There was not even 
room for incredulity as to the fact ; the less, in that the appa- 
ratus employed, consisting of a glass tube, a bar of common 
pith, and an ordinary candle, was so extremely simple. The 
machine, if indeed it was worthy of that name, went naturally 
into the category of those apparently trivial but really complex 
and pregnant combinations of common materials which, when 
once constructed, have each of them formed a beacon and signal 
post on the great high road of scientific discovery. That this 
was actually the attitude of the scientific mind may be seen 
from the words used by the President of the Royal Society in 
presenting the gold medal to the discoverer of the radiometer. 
“ It is the mystery,” said Dr. Hooker, u attending this pheno- 
menon that gives it its great importance. There is evidently 
some action going on with which we are not at present ac- 
quainted ; and there is no saying what a thorough investigation 
into the cause of the phenomenon may lead to.” 
striking were the phenomena which it for the first time brought 
