of Small Floating Bodies. 417 



pquid, which gives origin to a tensile elastic reaction resulting 

 in the development of a force tending to elevate or depress the 

 liquid according as its terminal surface adjacent to the solid is 

 concave or convex. The actual existence of such an elastic 

 contractile film at the bounding surfaces of liquids is abund- 

 antly verified by numerous conclusive experiments with films 

 of soapy water," as well as by the whole class of striking phe- 

 nomena rendered prominent by the admirable researches of 

 Plateau,* and the equally satisfactory investigations of Dupref 

 and of Quincke.^ 



Even according to the more exact mathematical theories of 

 ■■■apilhirily of Laplace and of Poi.sson. the explanation of this 

 class of phenomena is not altogether free from ambiguity. 

 Thus, in Laplace's investigation, as the pressure of the atmos- 

 phere appears as a prominent element in producing the mo- 

 tions of such floating bodies, the student is naturally perplexed 

 when he is confronted by the somewhat awkward fact, that 

 a are entirely independent of the pressure 

 to which the apparatus is exposed ; as was long ago proved by 

 the experiments in vacuo executed by the members of the 

 "Academia del Cimento" of Florence. It is proper to add, 

 however, that a critical examination of the explanation given 

 by Laplace as well as by Pois8on,§ very clearly indicates, that, 

 when the effective forces are considered, the pressure of the 

 ;itrnns|.hcre is practieallv eliminated from their equations ;— so 

 fl'at linallv the forces actually in operation, which produce -the 

 tendency of such bodies to approach or to recede from one 



Nevertheless inasmuch as Laplace's explanation contains the 

 pressure of the atmosphere as a term, while at the same time it 

 makes the effective force equivalent to a modification of hydro- 

 static pressure, which is negative or positive according as the 

 surface of the liquid adj (cent to the solid bodies is concave or 

 convex; it is by no means surprising that the idea of atmos- 

 pheric pressure" should have been associated with these phe- 

 nomena. Hence, we find that many first-class physicists, such 

 as Lame, Desains. .lamin. Kveretr. and others, introduce the 



