694 Chronicles of Science. [Oct., 



carrying of the instrument from the Minories to Kew Observatory, 

 and subsequently to the Eoyal Society without affecting the readings 

 may be taken as evidence that with ordinary care the spectroscope can 

 now be used with reliance as to the rigidity of its construction, thus 

 fulfilling the conditions which are indispensable for obtaining correct 

 observations. 



Heat. — In a former number we gave a brief account of some 

 experiments by Professor Tait and Mr. Stewart on the phenomenon of 

 the heating of a disc by rapid rotation ; some further results have lately 

 been communicated by these gentlemen to the Eoyal Society. In their 

 apparatus a slowly revolving shaft is carried up through a barometer 

 tube, having at its top the receiver which it is wished to exhaust. 

 When the exhaustion has taken place it is evident that this shaft will 

 revolve in Mercury. In the receiver the shaft is connected with a 

 train of toothed wheels, and ultimately causes a circular disc to revolve 

 125 times for each revolution of the shaft. Two insulated wires, con- 

 nected with a Thompson's reflecting galvanometer, are carried through 

 two holes in the bed-plate of the receiver, and are then connected with 

 a thermo-electric pile having the usual reflecting cone attached to it. 

 The outside of the pile and of its attached cone is wrapped round with 

 wadding and cloth, so as to be entirely out of the reach of currents of 

 air. The vacuum-gauge is on the syphon principle, and there is every 

 reason to believe that it is perfectly deprived of air ; and it is only 

 necessary to add, that the whole is covered over with an airtight glass 

 shade, 15 inches in diameter and 16 inches high. The galvanometer 

 and thermo-electric pile were sufficiently delicate, that if the tem- 

 perature of the disc were to rise 1° Fahr. this would be denoted by a 

 change in the position of the line of light equal to fifty divisions of the 

 scale. In these experiments the disc is rotated rapidly for half a 

 minute, making 2,500 revolutions, and the heating effect was recorded 

 by the pile. The object of this paper is to investigate the origin of 

 this heating effect. In the endeavour to account for this result, the 

 authors consider that we are reduced to choose between one of two 

 causes or to a mixture of the two. 



1. It may be due to the air which cannot be entirely got rid of. 



2. It is possible that visible motion becomes dissipated by an 

 ethereal medium, in the same manner and possibly to nearly the same 

 extent as molecular motion, or that motion which constitutes heat. 



3. Or the effect may be due partly to air and partly to ether. 



The authors give experiments to prove that only a very inconsider- 

 able portion of the effect observed depends upon the mass of air left 

 behind ; neither does the effect appear to be due to fluid friction. 



M. Dufour, of Lausanne, has made some experiments to ascertain 

 whether other gases behaved like atmospheric air in the phenomenon 

 of ebullition under different pressures. He employed hydrogen, car- 

 bonic acid, and coal gas, and found that when water saturated with 

 either of these gases was heated to boiling in an atmosphere of the 

 same gas, the phenomenon proceeded exactly as if the liquid were in 

 the presence of air. The ebullition showed nothing unusual, and the 



