410 Presents. [Mar. 2, 



A powerful magnet was now brought near the moving arms. They 

 immediately stopped, and at the same time the glass envelope commenced 

 to revolve in the opposite direction to that in which the arms had been 

 revolving. The movement kept up as long as the candles were burning, 

 and the speed was one revolution in two minutes. 



The magnet was removed, the arms obeyed the force of radiation from 

 the candles and revolved rapidly, whilst the glass envelope quickly came 

 to rest and then rotated very slowly the same way as the arms went. 



The candles were blown out ; and as soon as the whole instrument had 

 come to rest a bar-magnet was moved alternately from one side to the 

 other of the radiometer, so as to cause the vanes to rotate as if they had 

 been under the influence of a candle. The glass envelope moved with 

 some rapidity (about one revolution in three minutes) in the direction 

 the arms were moving. On reversing the direction of movement of the 

 arms the glass envelope changed direction also. 



These experiments show that the internal friction, either of the steel 

 point on the glass socket, of the vanes against the residual air, or of both 

 these causes combined, is considerable. Moving the vanes round by the 

 exterior magnet carries the whole envelope round in opposition to the 

 friction of the water against the glass. 



As there is much discussion at present respecting the cause of these 

 movements, and as some misunderstanding seems to prevail as to my 

 own views on the theory of the repulsion resulting from radiation, I wish 

 to take this opportunity of removing the impression that I hold opinions 

 which are in antagonism to some strongly urged explanations of thesa 

 actions. I have on five or six occasions specially stated that I wish to keep 

 free from theories. During my four years' work on this subject I have 

 accumulated a large fund of experimental observations, and these often 

 enable me to see difficulties which could not be expected to occur to an 

 investigator who has had but a limited experience with the working of 

 one or two instruments. 



Presents received, March 2, 1876. 



Transactions. 



Birmingham : — Institution of Mechanical Engineers. Proceedings, 



1875. No. 2 (April). 8vo. The Institution. 

 Edinburgh : — Royal Scottish Society of Arts. Transactions. Vol. VIU. 



Part 5 ; Vol. IX. Part 1, 2. 8vo. 1873-74. The Society. 



London :— East-India Association. Journal. Vol. IX. No. 1-3. 8vo, 



1875-76. The Association. 



Linnean Society. Journal. Zoology, Vol. XII. No. 60-62. 8vo. 



1876. The Society. 



