172 ANNUAL OF SCIENTIFIC DISCOVERY. 



the t^reatest depths with certahity, and with a rapidity which 

 hardly admits of a limit. In a recent experiment the instrument 

 rose IVom the bottom at the rate of 20 feet in a second, or of a 

 mile in less than 4i minutes. They believe that a soundin*:: in 

 2,000 fathoms water will ultimately be made easily in less tlian 

 15 minntes. The time occupied in a sounding of this depth by 

 those emjiloyed l)y the United States government in sounding be- 

 tween Iivland and Newfoundland, preparatory to hiying the At- 

 lantic cable, was ordinarily 6 or 7 hours. 



STEWART AND TAIT's EXPERIMENTS ON THE HEATING OF 

 BODIES BY ROTATION IN VACUO. 



Since the theory of a universal, all-permeating, elastic ether, 

 far more subtile than any known gas, even when expanded to the 

 utmost by mechanical means, has been found to account for the 

 phenomena of light and heat more perfectly than any other, the 

 actual demonstration of its existence has been a desideratum. 

 The experiments described in the present article, altiiough to our 

 minds not at all satisfactory, were undertaken to prove the real 

 existence of ether. 



The experiments are those of Balfour Stewart, F.R.S., Su- 

 perintendent of Kew Observatory, London, and P. G. Tait, M.A., 

 of Kdinburgh. 



These gentlemen, having obtained certain results in air, were 

 encouraged to construct an apparatus wherewith to procure rota- 

 tion in vacuo. 



In this apjDaratus a slowly revolving shaft is carried up through 

 a barometer tube, having at its top the receiver w'hich is to be 

 exiiausted. When the exhaustion has taken place, the shaft con- 

 nected with the mnltiplying gear revolves in mercury. Tiie 

 train of toothed wheels causes the disc of alnminum to revolve 

 125 times for each revolution of the shaft. The thermo-electric 

 pile, the most delicate thermometer or test of heat, is connected - 

 by two wires carried through two holes in the bed-plate of the 

 receiver Avith a Tiiompsoirs rellectiiig galvanometer needle. 

 The outside of the thermo-electric i)ile and its attached cone was 

 wiapped round with wadding and cloth, so as to be entirely un- 

 aflected by currents of air. 



During these exiDcriments the disc of aluminum was rotated 

 rapidly for half a minute, and a heating eflect was, in conse- 

 quence of the rotation, recorded ijy tiie thermo-electric pile. 



To obviate the objection that the electric currents which take 

 phice in a revolving metallic disc might alter the zero of the gal- 

 vanometer, the position of the line of light was read before the 

 motion began, and inunediately after it ceased, the difl'erence be- 

 m^ taken to denote the heating eflect produced by rotation. 



The thermometric value of the indications given by the gal- 

 vanometer was found in this way : " The disc was removed from 

 its attachment and laid uj)()n a mercury-bath of known tempera- 

 ture. 1l was then attached to its spindle again, being in this 



