1887.] NEW-YORK MICROSCOPICAL SOCIETY. 3 



I am under the impression that light in some way is the cause. 

 We see the radiometer turn when a ray strikes its veins. Per- 

 haps each of the moving particles is exposing facets, which are 

 light and dark by turn, to the upward ray of light in the micro- 

 scope, and as the particle moves, other facets are exposed, and 

 thus as long as the ray passes, so long will the particles move. 

 The refractive index of the water may in some way affect the facets 

 of the particles ; so also the combination of the glass slide and 

 the water may work together to this end. Thus a facet which 

 is bright when the particle is in one position will perhaps be dark 

 when the particle is in another position, and thus the veins of 

 each of these minute radiometers may be for each particle limit- 

 less in number and ever changing in hue. I have taken two 

 bottles, subjecting them to precisely the same conditions. In 

 each I placed water in which particles of " flake-white " were 

 suspended. One bottle I kept in the light, day and night for a 

 week, the other in total darkness for the same period. The 

 bottle exposed to the light appeared at the end of the period to 

 contain a greater number of particles moving in it than the bot- 

 tle which had been in the dark. This difference was visible to 

 the naked eye. The bottle exposed to the light being the one 

 which contained at the end of the time the most turbid fluid. 

 I have not been able to confirm the truth of this experiment. 

 In fact experiments with vermilion did not show the same result, 

 or else the difference between the bottles was so slight as not to 

 be noticeable. These experiments could be carried on and im- 

 portant results could perhaps be reached through the lessons 

 they taught. Any explanation of the mysterious movement 

 would be of interest. 



