6 On the Action of the Pollen of Plants, 



that the molecules of mineral substances should possess this 

 power, can only be admitted upon the most rigorous scrutiny. 



I have made repeated observations on several mineral sub- 

 stances, which Mr. Brown says are chiefly composed of these 

 active molecules ; and though in some instances I was at first 

 persuaded that I had seen the motions of the molecules similar 

 to those of the smallest species of Infusoria, a more careful 

 examination proved that I was mistaken, and that the motions 

 were derived from causes that had not been properly appre- 

 ciated. In these experiments it is absolutely requisite to em- 

 ploy fresh-distilled or fresh-boiled water. The Thames water 

 and water in cisterns generally contain numerous animalcules. 

 I chiefly made use of single lenses from -[V to oV of an inch 

 focal length, varying in magnifying power, from 100 to 220 

 times in linear dimensions : the use of the compound micro- 

 scope is, I think, inadmissible in such delicate observations. 

 With the lowest of the above-mentioned powers, a particle less 

 than 1 0,^0 0^ part of an inch in diameter is distinctly perceptible, 

 and the form of a particle of twice that diameter may be ob- 

 served.* To make use of higher powers than what are abso- 

 lutely required, render's the examinations more difficult, and 

 the result more uncertain. 



To obtain glass in a highly comminuted state, I took the 

 powder-blue used by laundresses, which I still farther tritu- 

 rated. The small portion of the oxide of cobalt which enters 

 into the composition of this glass, could not be supposed to 

 paralyse the action of the molecules, as all the metals that can 

 be reduced to powder are said to contain these active molecules. 



By making use of powder-blue, I had the advantage of seeing 

 when all the larger particles were deposited. Among other sub- 

 stances which I more particularly examined, were finely pow- 

 dered adhesive slate, mountain cork, quartz, flint, and kaolin, 

 from a specimen of the best kind used in the manufacture at 

 Sevres, given me by M. A. Brongniart. When a drop of water 

 containing any of these substances was placed under the micro- 

 scope, I perceived particles in motion, which continued for 

 some time, and then was scarcely discernible, but on laying my 

 hand upon the table the motion recommenced, and was evi- 

 dently produced by a current in the drop; although many 

 particles appeared to be more influenced by it than others, 

 which occasioned a change in their relative positions. Hence 

 I became convinced, that in order to make the experiment 



* According to Sir William Herschell, though an object which subtends 

 a visual angle less than a minute may be perceived, yet, to ascertain the 

 form of it, it should subtend two minutes and a half 



