in organic and inorganic Bodies. 169 



My manner of estimating the absolute magnitude and uni- 

 formity in size of the molecules, found in the various bodies 

 submitted to examination, was by placing them on a micro- 

 meter divided to five thousandths of an inch, the lines of which 

 were very distinct; or more rarely on one divided to ten 

 thousandths, with fainter lines, not readily visible without the 

 application of plumbago, as employed by Dr. Wollaston, but 

 which in my subject was inadmissible. 



The results so obtained can only be regarded as approxi- 

 mations, on which perhaps, for an obvious reason, much re^ 

 liance will not be placed. From the number and degree of 

 accordance of my observations, however, I am upon the whole 

 disposed to believe the simple molecule to be of uniform size, 

 though as existing in various substances and examined in cir- 

 cumstances more or less favourable, it is necessary to state 

 that its diameter appeared to vary from Tj,£oo"th to 2o%o~oo tn 

 of an inch # . 



I shall not at present enter into additional details, nor shall 

 I hazard any conjectures whatever respecting these molecules, 

 which appear to be of such general existence in inorganic as 

 well as in organic bodies; and it is only further necessary 

 to mention the principal substances from which I have not 

 been able to obtain them. These are oil, resin, wax, and sul- 

 phur; such of the metals as I could not reduce to that minute 

 state of division necessary for their separation ; and finally, 

 bodies soluble in water. 



In returning to the subject with which my investigation 

 commenced, and which was indeed the only object I ori- 

 ginally had in view, I had still to examine into the probable 

 mode of action of the larger or peculiar particles of the pollen, 

 which, though in many cases diminished in number before the 

 grain could possibly have been applied to the stigma, and 

 particularly in Clarckia, the plant first examined, were yet 

 in many other plants found in less diminished proportion, 

 and might in nearly all cases be supposed to exist in suffi- 

 cient quantity to form the essential agents in the process of 

 fecundation. 



I was now therefore to inquire, whether their action was 

 confined to the external organ, or whether it were possible to 



* While this sheet was passing through the press, Mr. Dollond, at my re- 

 quest, obligingly examined the supposed pollen of Equisetum virgatum with 

 his compound achromatic microscope, having in its focus a glass divided into 

 10,000ths of an inch, upon which the object was placed ; and although the 

 greater number of particles or molecules seen were about -g-Bvcnnrth, yet the 

 smallest did not exceed ^ ^ th of an inch. 



New Series. Vol. 4. No. 21. Sept. 182S. Z follow 



