1894.] 31ICR0SC0PICAL JOURNAL. 251 



it must have been very small. Moreover, the evidence is cer- 

 tainly here, to show that even if the movement were intensified 

 by light or heat, that was the only influence that could be as- 

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

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

 metric measurements of the range of movement at different tem- 

 peratures completely bore out this conclusion.'' 



The Red Wave oj Light. — The opinion of Bache is this: 



" The theory of Herr Weiner, that the movements are due to 

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

 single fact that, as may be proved by experiment, one may in- 

 terpose 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 dis- 

 cussion." 



Electric Currents. — The galvanic current has been passed 

 through liquids filled with particles without the slightest visible 

 effect upon them. 



Evaporation. — It was conceived that evaporation might be 

 accompanied with a series of minute explosions which produce 

 shocks that could manifest themselves through the mass of an 

 aqueous solution, in the form of minute movements of finely 

 divided matter held in instable equilibrium by suspension in 

 the fluid. Bache had satisfactorily eliminated nearly all other 

 hypotheses and held this one for final examination. He says : 



" At this point I encountered an obstacle. My high powers 

 of the microscope were both water-immersion lenses. It seemed, 

 therefore, that even when I had had the drop of liquid under 

 observation, sealed beneath a cover glass, I might have in- 

 cluded, by the use of the water-immersion lens itself, an evapor- 

 ating surface which might have produced the optical illusion 

 of the movement of the particles in suspension. I proceeded, 

 however, with my experiments, upon the assumption that this, 

 as the event proved to be the case, was not true, and meanwhile 

 procured from Vienna a one- fifteenth dry lens by Reichert, the 

 highest power of dry lens that he makes, 



