218 Dr Brewster on the motions of the Molecules of Bodies. 



and spheres of gypsum into artificial pearls ; but it exhibited 

 no organized structure, and consequently indicated no polari- 

 ty in the elementary spicula. 



In making these experiments, I was often surprised by a 

 singular variation in the whiteness of the large plate of fluid 

 when spread over the square of glass. It sometimes appear- 

 ed to be quite dark, and at other times to recover its white- 

 ness without any apparent cause. This, however, I found to 

 arise from currents of air arising from my own motion across 

 the room, and I could make the fluid appear white or dark at 

 pleasure, by merely blowing over its surface. When the fluid 

 surface was in a state of rest, the spicula settled in certain po- 

 sitions in relation to a vertical line ; but whenever a breath of 

 air affected the fluid they were thrown into new positions, and 

 reflected the incident light in a different manner. 



Owing to the great extent of surface which was thus expos- 

 ed to accidental impressions, the movements of the spicula 

 were much more lively than when they were examined in small 

 portions of fluid ; but the slightest examination was sufficient 

 to satisfy me that their movements were entirely the result of 

 the position of unstable equilibrium which they occupied in the 

 fluid medium. 



Since these experiments were made, I have observed analo- 

 gous motions, though arising from a different cause, in the 

 juice of the Semecarpus anacardium^ and I am persuaded 

 that they will be found in all organized fluids. When this 

 fluid, or a portion of the black Indian varnish, (which is a 

 mixture of the sap of the Semecarpus anacardium with that of 

 the Jowar^) is placed between two plates of glass, and illumi- 

 nated in the microscope by the sun's rays, the particles seem 

 to be all in motion, and there appears a most singular and ra- 

 pid play of colours, arising from the inflexion of the light 

 which passes between the organized molecules. The very 

 same phenomenon has been observed by M. Dutrochet in 

 blood taken either from the veins or arteries of an animal, and 

 the motion of its particles ceases only when the blood coagu- 

 lates. 



In examining the motions of the granules of pollen suspend- 

 ed in water, (which I have done since the publication of Mr 



