MICROSCOPES. 251 



submitted to the deep powers of the microscope ; to sepa- 

 rate the molecules from the glass itself, either pound it very 

 fine, or gently rub together the unpolished edges of two 

 pieces, having previously wetted them the produce can 

 then be transferred to a drop of water. 



The figure of the molecules is spherical ; they are so 

 minute, that four hundred millions of them would not occupy 

 greater space than a superficial square inch. Their motion 

 is very vivid, and consists, not only of a change of place in 

 the fluid, manifested by alterations in their relative positions, 

 but also, not unfrequently, of a change of form in the particle 

 itself; each molecule appears to revolve upon its axis: in 

 fact, the whole of the motions are very similar to those of 

 the most minute kind of animalcules inhabiting water. 



Some persons have considered the motion to result from 

 the evaporation of the fluid and the action of the breath of 

 the observer upon its surface : this is proved not to be the 

 case, by covering the water with a thin piece of talc, when 

 the motions continue unaltered ; it has likewise been urged 

 that these spherical molecules may be hollow, and that the 

 motion is produced by the water entering them, thereby 

 displacing the air contained in them were this the case 

 the action must soon subside, which does not take place; 

 besides, the molecules are proved to be suspended within 

 the fluid, by bringing the surface to the true focus, when a 

 variety of irregular particles (distinct from the molecules) 

 will be discovered, evidently acted upon by exterior causes. 



When it is considered that there is not the slightest dif- 

 ference in the general figure of these active molecules (let 

 the substance be what it may from which they are separated), 

 it will be conceded that their identity gives them a character 

 which makes it difficult to prove their figure and motions to 

 be the result of mere chance, exterior mechanical causes, or 

 optical delusion. 



Infusoria, or Animalcula in Vegetable Infusions. The 

 smallest living creatures we are acquainted with are the 

 animalcula in fluids ; they afford a wonderful scope for 

 inquiry, and nothing is more capable of affording instruc- 

 tion combined with amusement, than researches into the 

 secrets of nature in the more minute parts of her works, 

 and they present to view most surprising wonders hitherto 

 unknown ; for who would or could have imagined that, in a 



