SLATES. 



(Part of a Lecture delivered in the Royal Institution of Great Britain, 

 June 6, 1856.) 



WHEN the student of physical science has to investigate 

 the character of any natural force, his first care must be to 

 purify it from the mixture of other forces, and thus study 

 its simple action. If, for example, he wishes to know how 

 a mass of liquid would shape itself, if at liberty to follow 

 the bent of its own molecular forces, he must see that these 

 forces have free and undisturbed exercise. We might, per- 

 haps, refer him to the dew-drop for a solution of the ques- 

 tion ; but here we have to do, not only with the action of 

 the molecules of the liquid upon each other, but also with 

 the action of gravity upon the mass, which pulls the drop 

 downward and elongates it. If he would examine the 

 problem in its purity, he must do as Plateau has done, de- 

 tach the liquid mass from the action of gravity ; he would 

 then find the shape to be a perfect sphere. Natural pro- 

 cesses come to us in a mixed manner, and to the unin- 

 structed mind are a mass of unintelligible confusion. Sup- 

 pose half a dozen of the best musical performers to be placed 

 in the same room, each playing his own instrument to per- 

 fection, but no two playing the same tune ; though each in- 

 dividual instrument might be a source of perfect music, still 

 the mixture of all would produce mere noise. Thus it is 

 with the processes of Nature. Here mechanical and mo- 

 lecular laws intermingle and create apparent confusion. 

 Their mixture constitutes what may be called the noise of 



