252 THE AMERICAlSr MONTHLY [Aug. 



" I had already obtained for high-power lenses a fihn of 

 liquid thin enough to be observed through all its strata, free of 

 air within the cell, and protected from evaporation by being 

 hermetically sealed. Any ordinary manufactured cell is too 

 deep, and with all precautions taken contains a little air. On 

 the other hand, the mere cover-glass superposed on a glass slide 

 contains too slight a depth of fluid. I made a cell by using 

 gum-shellac traced in a circlet on a glass slide, which cell, when 

 l)artially dried, is filled to the brim with the liquid to be ob- 

 served upon, whereupon the cover-glass is pressed into the 

 yielding gum, thereby expressing the contained air with the 

 superfluous liquid, when the product, dried over nighty is fit 

 for use on the following evening. One slide, prepared in this 

 manner and filled with a slightly tinted solution of carmine 

 from cochineal, had been observed upon by me for weeks, with 

 a one-tenth water-immersion lens, and afterwards, upon the ar- 

 rival of the one-fifteenth dry lens, was observed upon without 

 showing any variation in the range and vividness of movement 

 of the particles subjected to examination. I have even covered 

 the whole microscope with a pall of thick, black, woolen cloth, 

 so that not a ray of light could enter it, either through the 

 cover glass or the eye-piece, and then carefully placing the e3'e 

 close to the eye-piece, have suddenly thrown light upon the 

 cover-glass, when the Brownian movement among the particles 

 was perceived in as active play as ever. I have, therefore, con- 

 cluded, from all these experiments, that neither heat nor light, 

 nor electricity, nor magnetism, nor mechanical shock, nor 

 finally evaporation, is operative in producing the movements ; 

 in a word, that the 2>articles move uninfluenced by these forces." 



The Fluid Moves the Particles. — All other possible suppositions 



having been eliminated, Bache has concluded that it is not the 



particles which are moved by their own energy, or moved by 



any enercry directly imparted to them from outside sources, 



but thr f *, is the fluid that moves them. Accordingly he 

 argues as to., j^^^^^ . 



" Tf cheir o 



';wn energy moves the particles, we should see them 



at the sa .^^^^ obedient also to the law of gravitation among 



^"^"^*^® ^'^', manifested as the resultant of whatever forces are 



in piay,^ areas, although they must be obedient to the law of 



gravi a among themselves, its effects, and generally, as 



