342 Analysis of Scientific Books and Memoirs. 



primary combinations of these, were not unfrequently met with, and in 

 motion generally more vivid than that of the simple molecule, their motion 

 consisting in turning usually on their longer axis, and then often appear- 

 ing to be flattened. Such oval particles were found to be numerous and 

 extremely active in white arsenic. 



As mineral bodies which had been fused contained the moving molecules 

 as abundantly as those of alluvial deposits, I was desirous of ascertaining 

 whether the mobility of the particles existing in organic bodies was in any 

 degree affected by the application of intense heat to the containing sub- 

 stance. With this view small portions of wood, both living and dead, 

 linen, paper, cotton, wool, silk, hair, and muscular fibres, were exposed to 

 the flame of a candle, or burned in platina forceps, heated by the blowpipe ; 

 and in all these bodies so heated, quenched in water, and immediately sub- 

 mitted to examination, the molecules were found, and in as evident motion 

 as those obtained from the same substances as before burning. 



In some of the vegetable bodies burned in this manner, in addition to 

 the simple molecules, primary combinations of these were observed, con- 

 sisting of fibrils having transverse contractions, corresponding in number, 

 as I conjectured, with that of the molecules composing them ; and those 

 fibrils, when not consisting of a greater number than four or five mole- 

 cules, exhibited motion resembling in kind and vivacity that of the mine- 

 ral fibrils already described, while longer fibrils of the same apparent dia- 

 meter were at rest. 



The substance found to yield these active fibrils in the largest propor- 

 tion and in the most vivid motion, was the mucous coat interposed be- 

 tween the skin and muscles of the haddock, especially after coagulation by 

 heat. 



The fine powder produced on the under surface of the fronds of seve- 

 ral ferns, particularly of Acrostichum cahmelanos, and the species nearly 

 related to it, was found to be entirely composed of simple molecules and 

 their primary fibre-like compounds, both of them being evidently in mo- 

 tion. 



There are three points of great importance which I was anxious to as- 

 certain respecting these molecules, namely, their form, whether they are 

 of uniform size, and their absolute magnitude. I am not, however, en- 

 tirely satisfied with what I have been able to determine on any of these 

 points. 



As to form, I have stated the molecule to be spherical, and this I have 

 done with some confidence ; the apparent exceptions which occurred ad- 

 mitting, as it seems to me, of being explained by supposing such parti- 

 cles to be compounds. This supposition in some of the cases is indeed 

 hardly reconcileable with their apparent size, and requires for its support 

 the further admission, that, in combination, the figure of the molecule may 

 be altered. In the particles formerly considered as primary combinations 

 of molecules, a certain change of form must also be allowed ; and even the 

 simple molecule itself has sometimes appeared to me when in motion to 

 have been slightly modified in this respect. 



My manner of estimating the absolute magnitude and uniformity in size 



