42 M. G. Van dor Monsbruo-ghc on the Variations 



minuto. Is not this tlio reason that, according to the obser- 

 vations of Sanssuro and Fournet, the minute drops forming 

 chjuds and mists can float in the strata of air whose; tempera- 

 ture is much below zero, without assuming the solid state? 



What has just been said of a series of n globules weighing 

 together tlie unit of weight applies equally to each isolated 

 th'op ; in fact, if V represents the volume, and 8 the specific 

 gravity of the liquid forming the drop, we have 



K = k — . 



Y8 



S 

 Now the ratio ^ increases as the volume of the drop dimi- 



V . (PT , 



nishes ; and consequently, since -7-^ is negative, the smaller 



the diameter of the drop the greater will be the value of K. 

 Does not this explain how M. Mousson* was able, at very low 

 temperatures, to keep in the liquid state globules of water of 

 less than ^ millim. diameter disposed upon a surface which 

 they did not wet ? In the same way Mr. Tomlinson f, more 

 than thirty-five years since, could see minute drops of water, 

 alcohol, ether, roll upon the surface of a fixed oil raised to 

 more than 200° C. 



In the case where T designates, not the potential energy of 

 a free liquid surface, but that of a surface connnon to two 

 liquids which do not mix, similar effects to the preceding can 

 be obtained. Thus M. L. Dufour J obtained globules of water 

 in the liquid state innnersed in a mixture of chloroform and 

 oil, although the temperature descended as low as — 10°C., 

 and even —20° for the smallest spherules. He verified still 

 more marked effects with globules of fused phosphorus or sul- 

 phur in the midst of a liquid of the same density. 



If the question be of the surface of contact of a solid and a 

 liquid which wets the latter, we shall have to ascertain the 



sign of -JY, in order to foresee the quantity of heat necessary 



to a variation of potential energy in the surface of contact ; if 

 the sign be negative, we must again conclude that K also in- 

 creases with the surface iS. Now a great number of experi- 



* " Sur la fusion et la solidification de I'eau," Bibl. Univ. de GtWve, 

 1858, t. iii. p. ^1)0. 



t Student's Manual of Natural Philo^oplij', p. 553. 



\ ''Sur la congelation de I'eau et sur la Ibrmation de la giele," ^/Z>/. 

 Um'v. 1801, t. X. p. .S4(). 



