250 THE AMERICAN MONTHLY [Aug. 



speaking, some of which are no greater in diameter than 1-100,- 



000 of an inch, seen under various powers capable of magnify- 

 ing from 650 to 1300 diameters. Accordingly, I have placed 

 the particular fluid under examination in the lines of force of a 

 permanent magnet, with the magnet on one side and the keeper 

 on the other of the drop of fluid. Concentrating the gaze on 

 individual particles, to observe if their movement were modi- 

 fied, and then on others in succession, and often repeating the 

 experiment, nothing could be observed other than the move- 

 ments existing before the magnet had been brought into requi- 

 sition. The only kind of particles susceptible to the influence 

 of the magnet were thofe of precipitated iron, but iron is always 

 obedient to the magnet." 



Heat and Cold Insufficient. — Bache reports : 



" Heat I ajiplied in various ways, either irregularly or in an 

 endeavor to distribute it as equally as possible on the glass 

 slide on which the particular experiment was made. Mere cur- 

 rents are set up during the adjustment of temperature from 

 radiation. At the same time one can observe and differentiate 

 the motions due to the Brownian movements, the motions 

 along currents, and also the motions from terrestrial gravity, 

 if any, exhibited by particles, if the specific gravity of the sub- 

 stance be great, and the microscoi^e 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, 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, corresponding with their alternate subjection to 

 heat and cold. There were occasions in which I thought that 



1 observed acceleration from light, but I always ended by im- 

 puting it to the force of imagination, and if it were not justly 

 ascribable to that cause, the fact that it could be so ascribed, is 

 proof i)0sitive that if, through the influence of light and heat, 

 any intensification of the movements of the particles took i)lace, 



