1894.] I'l [Bache. 



the specific gravity of the substance be great, and the microscope 

 be set at an angle with the verticaL 



Cold I also applied, putting the slides with their cover-glasses in 

 a freezing mixture of broken ice and water, and reducing them to a 

 very low temperature. Still the movements went on as apparently 

 unmodified as ever. Herr Exner says, it will be remembered, that 

 glycerin, which under ordinary conditions shows absolutely none, 

 or almost no molecular movement, shows it clearly when warmed up 

 to the temperature of fifty degrees centigrade. In all the finely 

 divided bodies, however, which I examined, there seemed to be 

 no increase or diminution in the intensity of the movements, cor- 

 responding with their alternate subjection to heat and cold. There 

 were occasions in which I thought that I observed acceleration from 

 light, but I always ended by imputing it to the force of imagina- 

 tion, and if it were not justly ascribable to that cause, the fact that 

 it could be so ascribed, is proof positive that if, through the influence 

 of light and heat, any intensification of the movements of the parti- 

 cles took place, it must have been very small. Moreover, the evi- 

 dence is certainly here, to show that even if the movement were 

 intensified by light or heat, that was the only influence that could 

 be ascribed to them, that light and heat could not be deemed the 

 cause of the movement. And lastly, Herr Wiener's micrometric 

 measurements of the range of movement at different temperatures 

 completely bore out this conclusion. 



The theory of Herr Wiener, that the movements are due to the 

 action of the red-wave of light and heat is refuted by the single 

 fact that, as I have proved by experiment, one may interpose at 

 pleasure between the source of light or heat and the particles, either 

 a violet glass or a red glass, without being able to observe the 

 slightest alteration in the movements, either as to their range or 

 their velocity. That is to say, red rays may be either partially 

 excluded or selectively admitted, without diminishing or increasing 

 the liveliness of movement. Hence light can have nothing to do 

 with the phenomenon under discussion, and I have just shown, 

 through the citation of the freezing mixture experiment, that heat 

 can have nothing ro do with it. 



I have reserved to the very last the discussion of the question as 

 to whether or not the shock, if any there be, from evaporation can 

 have anything to do with the movements, although this was a point 

 that entered into my first investigations. I have reserved it to the 



