44 Mr Brown on Active Molecules. 



sion of the experiment; for by mixing a very small proportion 

 of oil with the water containing the particles, microscopic drops 

 of oil of extreme minuteness, some of them not exceeding in size 

 the particles themselves, will be found on the surface of the drop 

 of water, and nearly or altogether at rest ; while the particles in 

 the centre or towards the bottom of the drop continue to move 

 with their usual degree of activity. 



By means of the contrivance now described for reducing the size 

 and prolonging the existence of the drops containing the par- 

 ticles, which, simple as it is, did not till very lately occur to me, 

 a greater command of the subject is obtained, sufficient perhaps 

 to enable us to ascertain the leal cause of the motions in ques- 

 tion. 



Of the few experiments which I have made since this manner of 

 observing was adopted, some appear to me so curious, that I do 

 not venture to state them until they are verified by frequent and 

 careful repetition. 



I shall conclude these supplementary remarks to my former 

 observations, by noticing the degree in which I consider those 

 observations to have been anticipated. 



That molecular m as sometimes confounded with animalcular 

 motion by several of the earlier microscopical observers, appears 

 extremely probable from various passages in the writings of 

 Leeuwenhoek, as well as from a remarkable paper by Stephen 

 Gray, published in the 19th volume of the Philosophical Trans- 

 actions. 



Needham also, and Buffian, with whom the hypothesis of or- 

 ganic particles originated, seem to have not unfrequently fallen 

 into the same mistake. And I am inclined to believe that Spal- 

 lanzani, notwithstanding one of his statements respecting them, 

 has, under the head of Animaletti (V^dtimo oi'dine, included the 

 active molecules as well as true animalcules. 



I may next mention that Gleichen, the discoverer of the mo- 

 tions of the particles of the pollen, also observed similar mo- 

 tions in the particles of the ovulum of zea mays. 



Wrisberg and MuUer, who adopted in part Buffon's hypo- 

 thesis, state the globules, of which they suppose all organic bodies 

 formed, to be capable of motion ; and Muller distinguishes these 

 moving organic globules from real animalcules, with which he 



