1894.] MICROSCOPICAL JOURNAL. 249 



different figure also present analogous motions in like circum- 

 stances. 



Many Causes Suggested. — Among the surmises that have heen 

 made may be mentioned: (1) Gravitation or the attraction and 

 repulsion of the particles among themselves. (2) Currents con- 

 tained in the fluids. (3) Evaporation of the containing fluids. 

 (4) Energy derived from without the fluids, such as light, heat, 

 electricity, magnetism. (5) The molecular motion of the par- 

 ticles of the fluid itself. 



Gravitation and Currents Insufficient. — R. M. Bache has shown 

 this in saying : 



" Just as one sees a boat managed by an unskillful helmsman 

 pursue its erratic way in going about, being taken aback, or 

 heeled over by a flaw of wind, without for a moment attribut- 

 ing its movement to currents or any other cause but the true 

 one, so the constant observer of the brownian movements knows 

 full well that the particles themselves are moving, not being 

 moved by currents or by gravitatioa towards the earth or among 

 themselves. He, from the first, recognizes the fact that the 

 smaller the particles are, the more vivid is their movement. 

 He recognizes another, that, although many large particles do 

 not, as masses, move at all, yet the larger masses are all alive, 

 as it were, with smaller ones, seen clearly around their periph- 

 ery, on the silhouette of which they are seen plying like banks 

 of oars in an ancieat trireme. He is struck with and convinced 

 of still another thing, that whereas one might expect to find 

 that all particles would manifest an attraction for each other 

 through gravitation, and that the larger and largest, but all in 

 proportion to their relative size, would attract and absorb the 

 relatively smaller and smallest ones, nothing of the kind oc- 

 curs, but the smaller, down to the smallest, go their own way, 

 sometimes even touching the largest and bounding off and away 

 as if they do not, as indeed they do not visibly, submit to the 

 force of gravitation. Of course they cannot escape the influence 

 of gravitation, whether terrestrial or among themselves, but the 

 effect of gravitation upon them is masked, in what manner will 

 appear latter." 



Magnetism Insufficient. — Bache says ; 



" It seemed to me that magnetic earth-waves might affect 

 particles in such delicate suspension as those of which we are 



