Mr. Barlow on (he Magnetism developed hy Rotation. 93 



wards or downwards when they have been accidentally ex- 

 cited. The extreme limits between which every atmosphere 

 possessing these properties is contained are, on the one hand, 

 the atmosphere imagined by Dalton, in which every mass of 

 air retains the whole of its absolute heat without increase or 

 diminution ; and, on the other, the atmosphere of equable 

 temperature, in which a mass of air has the whole heat ab- 

 sorbed by rarefaction restored to it. In these extreme atmo- 

 spheres the only action which the aggregate exerts upon its 

 parts is pressure; and every partial mass, having the sources 

 of temperature entirely within itself, is indifferent to motion or 

 rest, since in either case the elasticity will equally balance the 

 external pressure. In any of the intermediate atmospheres, 

 when a mass of air shifts its place, its elasticity varies both on 

 account of the change of volume and the transference of heat ; 

 and as these two causes produce effects contrai'y to one an- 

 other, there is introduced a principle of stability tending to 

 destroy vertical motions upwards or downwards. By the 

 foregoing reasoning the investigation of the true atmosphere 

 is at least brought within certain limits. In proceeding fuither, 

 we must have recourse to other phaenomena, in order to parti- 

 cularize the individual case that alone agrees with nature in 

 all its properties. But we may here observe that the principle 

 of stability, which is evanescent in both the extreme cases, 

 must first increase and then decrease in passing from one to 

 the other. At some intermediate point it will therefore ope- 

 rate with a maximum effect; and it is not uni'easonable to 

 conjecture that this particular case, merely because it is sin- 

 gle, will be found to agree with the atmosphere of nature. 

 This, however, is a point to be inquired into, not one con- 

 clusively established. 

 Aug. 2, 1825. [To be continued.] James IvoRY. 



XII. Abstracts of a Scries of Papers lately read before the 

 Royal Society, Sfc. on the Magnetism developed by Rotation. 

 By Mess7s. Barlow, Christie, Babbage, Herschel, a7id 

 Marsh*. 



On the Magnetism imparted to Iron Bodies by Rotation. By 

 Peter Barlow, Esq. F.R.S. 



''I ""HE author's attention having been recalled to the consi- 

 ■* deration of the effects of rotation in altering the magnetic 

 influence of iron, in the course of speculations on the cause of 



the 

 • Thc;j;rcat importance of the experiments and investigations detailed 



in 



