90 Stewart and Tait Radiation from a Revolving Disk. [Feb. 23, 



obtained of considerable size and great lustre, closely resembling chlorate 

 of potassa in appearance. This body also contains sulphur. The second 

 substance, the quantity of which is comparatively small, crystallizes in 

 long thin plates. 



The oil, when treated with concentrated sulphuric acid, dissolves with a fine 

 purple colour, and from this solution water precipitates a crystalline body, 

 an organic acid remaining in solution, which forms a crystalline lime-salt. 



I have likewise subjected to destructive distillation the sulphobenzolates 

 of lime, ammonia, and copper. The two last yield very different products 

 from the soda-salt. 



I am at present engaged in examining these as well as the other bodies 

 mentioned in this Notice, and hope soon to be able to communicate to the 

 Society the results of my investigations. 



III. " Preliminary Note on the Radiation from a Revolving Disk." 

 By BALFOUR STEWART, M.A., F.R.S., and P. G. TAIT, M.A. 

 Received February 23, 1865, 



The authors having been led by perfectly distinct trains of reasoning to 

 identical views bearing on the dissipation of energy, have had preliminary 

 experiments made on the increase of radiation from a wooden disk on 

 account of its velocity of rotation, both in the open air and in vacua. 



These experiments were made with a very delicate thermo-electric pile 

 and galvanometer. In the experiments in the open air the disk was of 

 wood ; its diameter was 9 inches, and it was made to rotate with a velocity 

 somewhat less than 100 revolutions in one second. 



A sensible effect was produced upon the indicating galvanometer when the 

 disk was made to rotate, and this effect appeared to be due to radiation, and 

 not to currents of air impinging against the pile. In amount it was found to 

 be nearly the same as if the disk had increased in temperature 0> 75 Fahr. 



In the experiments in vacuo the diameter of the wooden disk was over 

 12 inches ; its velocity of rotation was about 100 revolutions in one second, 

 and the pile was nearer it than when in air. Under these circumstances, 

 with a vacuum of 06 in., an effect apparently due to radiant heat was ob- 

 tained, amounting to nearly the same as if the disk had increased in tem- 

 perature 1'5 Fahr. 



Bearing in mind the increased diameter of the disk, the effect is pro- 

 bably equivalent to that obtained in air, and these preliminary experi- 

 ments would tend to show that when a wooden disk is made to revolve 

 rapidly at the surface of the earth, its radiation is increased to an extent 

 depending on the velocity ; and it would appear that this effect is not 

 materially less in a vacuum of 0'6 in. than in the open air. 



The authors intend to work out this and allied questions experimentally, 

 and hope, if successful, to communicate the result to this Society. 



