2 JOURNAL OF THE [January, 



If a mounted slide is kept for a long time with one part lower 

 than the other, the particles will by gravity settle and compact 

 themselves in the low part of the cell, and then if the mass is so 

 compact that shaking the slide will not break it, the slide is spoilt. 



The stratum of water between the cover-glass and slide is not 

 equally filled with moving particles. Most of the particles which 

 are large enough to be observed satisfactorily are close to the 

 slide's surface, though smaller and more rapidly moving particles 

 are found in all parts of the stratum of water. If only these latter 

 could be enclosed in the ceH, I do not think they would ever be 

 affected by gravity and would not form themselves into a com- 

 pact mass. However, these particles are comparatively few, and 

 it seems impossible to crowd them into a mount — they seem to 

 require room and are not friendly. 



By mounting some material upon a ruled glass slide, it will be 

 seen by carefully focusing with a high power, that most of the 

 moving particles are on, or, are close to the surface of the slide. 

 There they move about, some sliding as it were, some rotating,some 

 moving in one direction and some moving in another direction. 

 Only the small particles seem to rotate. Almost all the particles 

 partake of several motions at once, sliding, rotating or partly 

 rotating, and bodily moving about at the same time. The motion 

 cannot be described, it must be seen. The smaller globules in 

 milk show the movement well, if the milk is confined in a cell. 

 If not in a cell, the flowing of the milk on the slide makes the ob- 

 servation difficult. The standard books, such as Carpenter, Beale, 

 etc., differ widely on this subject : Some say that heat increases 

 and others say that heat does not affect the movement, or, rapid- 

 ity of the movement of the particles, I have never found that heat 

 affects the movement one way or the other. To this end I have 

 illuminated the microscope by a ray of moonlight and have 

 found the movement the same, as when a strong ray of light from 

 a lamp was used. I have heated the slides on a hot stage up to 

 1 80° F. and above, and have found no change in the movement, 

 I have also used non-actinic light, but have found no change. 

 Some have attributed the movement to electricity, but it is diffi- 

 cult to see in what condition it could be and give such results. 

 It is a question whether the movement would be shown unless 

 the water was between two glasses, but I believe I have observed 

 it in an exposed drop of fluid, but of this I am not certain. 



