44 Geology, as illustrated by Chemistry and Physics. 



trustworthy measurements of degrees, ¥ £ ff , as can possibly 

 be expected from the difficulty of the calculation. The hypo- 

 thesis of the former liquid state of the earth acquired by this 

 means the highest degree of probability. 



Liquid substances, in consequence of the extreme mobility 

 of their particles, obey with the greatest readiness the action 

 of forces which tend to alter their external configuration. 

 Among these forces, gravity is that which, in comparison 

 with all others, is so preponderating as almost entirely to 

 obscure their action. It is only by observing very small liquid 

 masses, in which the relative action of gravity is much en- 

 feebled, that the influence of other forces upon the configura- 

 tion of these masses can be recognised. Thus small drops 

 of water and melted metals aggregate into spheres upon solid 

 surfaces when the mutual attraction of their particles is 

 greater than that between them and the surfaces upon which 

 they rest. If it be desired to study larger masses of liquid 

 bodies in their proper freely-assumed figure, we must con- 

 sider the earth and the other planets in the forms which 

 they have acquired through the united action of attractive 

 and centrifugal forces while in their original liquid state. 

 Theory points out that these masses must have assumed the 

 forms of more or less oblate spheroids, and observation 

 teaches us that such is really the case. 



Plateau, professor of natural history in Ghent,* conceived 

 the ingenious idea of placing large masses of fluids in cir- 

 cumstances which would neutralise the action of gravity 

 without their ceasing to be subject to the other forces which 

 tend to alter their exterior form. He effected this in a very 

 simple manner, by introducing a fatty oil, such as olive-oil, 

 into a mixture of water and alcohol, having the same specific 

 gravity as the oil. The influence of gravity on this oil was 

 entirely neutralised, for, as both liquids had equal densities, 

 the oil only occupied the place of an equal mass of the sur- 

 rounding liquid. Since fatty oils do not mix with a mixture 

 of alcohol and water, the former remained floating in the 

 surrounding liquid, and had perfect freedom to assume what- 



V; Poggcndorf'fl Annalen, Erganzungs, band ii.. p. 249, ct ?cq. 



