Intelligence and Miscellaneous Articles, 163 



the force diminishes, the effect decreases ; but as it is proportional 

 to the time, it is only necessary to wait till it becomes appreciable 

 and capable of being measured. 



These very special conditions appear to us of a nature to justify 

 the use of the pendulum for measuring attractive or repulsive forces, 

 however small they may be, and for comparing them to a common unit, 

 gravity. Those forces which are accessible to this mode of investi- 

 gation are, in the first place, all the physical forces, and then especi- 

 ally that of universal attraction, which might show itself, not by a 

 static effect of given magnitude, but by an action which is always 

 accumulating so as to produce a considerable perturbation. Ex- 

 periment has shown that all accidental causes may be eliminated 

 which tend to alter the small axis of the ellipse, that the method is 

 extremely sensitive, that it exhibits the feeblest electrical or mag- 

 netic actions. It will be understood that these researches will require 

 a considerable time. They are already commenced; we shall suc- 

 cessively publish the results. — Comptes Rendus, December 11, 1865. 



ON THE EXPANSION OF SATURATED VAPOURS. 

 BY M. A. CAZIN. 



Messrs. Rankine and Clausius deduced, in 1850, from the equa- 

 tions of the mechanical theory of heat the proposition that dry 

 saturated aqueous vapour condenses partially on expansion, and that, 

 conversely, it becomes superheated on compression, provided that 

 adjacent bodies neither furnish nor withdraw from it any heat. 



M. Hirn observed this about 1862. He verified, moreover, two 

 other consequences of the same equations ; that is, that bisulphide of 

 carbon under ordinary circumstances behaves like water, and that 

 ether behaves differently, becoming superheated by expansion, and 

 condensing partially by compression. 



M. Dupre has finally deduced from the equations of the theory 

 the more general proposition, that for each liquid there is a tempera- 

 ture at which its saturated vapour might undergo an infinitely small 

 expansion or compression with continued saturation ; that at a lower 

 temperature the expansion is accompanied by a condensation ; at a 

 higher temperature the contrary is the case. This follows from the 

 relations established by M. Regnault between the total heats of 

 vapours and the temperatures in his remarkable experiments. 



I have been charged by the Physical Committee of the Scientific 

 Association to verify this inversion. The apparatus constructed by 

 M. Golaz has been set up in one of the rooms of the Observatory. 

 In addition to M. Le Verrier, I wish to thank MM. Regnault and 

 Hirn for their valuable advice. 



The first researches were simply qualitative ; before determining 

 the temperature of inversion, I had to establish its existence. 



The principal part of the apparatus consists of a cylinder 60 cen- 

 timetres in length by 12 in diameter, with glass plates at its ends, 



