236 Scientific Intelligence. 
those who accept this theory the radiometer becomes an instru- 
ment of the very highest interest, affording as it does, another 
and very striking manifestation of molecular motion. Moreoy er, 
when we shall be able to overcome the experimental difficulties 
so as to estimate with certainty the force exerted under determin- 
ate conditions, we may hope to obtain by its aid a direct measure 
of absolute molecular magnitudes, 
We may be permitted to add to this notice a brief account of a 
few experiments made with the radiometer at Cambridge in the 
spring of 1876, soon after the instrument had ip received from 
Europe. We ‘became at once reatly sarerasta in the new phe- 
nomena, and with the aid of a skillful glass blower made more 
commu adem} 
and in a popular article in the Boston Daily Advertiser, we did 
' not otherwise publish our results, because we felt that the field had 
been in a measure preémpted by the a ea of the phenomena, 
who was then investigating the subject, and who, we felt sure, 
must dean at last to the same conclusions Witch we had reached. 
Our results can now add nothing to the strength of the theory, 
Moe has been since so well ata out by aan ects < 
of the i ia Bisa have never been—so far e kno 
aastirbed before, and being so aie that ity oii be easily 
repeated in any physical cabinet, a description of them, even 
this late day, may have an interest for cy of physic 
st experimented with a common radiometer beetue pe 
ned o i eam 
made at once this experiment. We placed an opaque screen ‘iear 
auntie ten petri et ait in a similar way cect only 
the uncoated faces ; when the wheel pagent to sb in the same 
ane although much more slowly than befor Again we 
ounted the revolutions. Lastly we counted the avelaaions while 
the beam shone on batt sides of the vanes as usual. We repeat 
the experiment se times, and were surprised at the remark- 
able constancy of ‘he results. They were as follows: 
Time of ten goby ee 
With both faces exposed ge ate 319 
With ——— = alone exposed ____- e's a 
ca faces ne ex 29" 
mmm wee eee 
