OF TRANSMITTING LIGHT. 341 



the naked eye, is apparently a perfect solution, under the microscope, with a high 

 power, exhibits particles of carbon, many of them so small as to be barely within 

 the limits of distinct vision, and what these are to a lower power, others may be 

 to the power which brings these into view. 



It may be conjectured that other substances, at present considered as opaque, 

 if examined in the same manner as that which I have applied to charcoal and 

 plumbago, may also be found to be translucent. Hitherto, I have succeeded only 

 with one, viz. iodine. When it is viewed in a very finely divided state, as in 

 the smallest crystals in which it can be obtained, and these allowed to be 

 attenuated by evaporation, and so reduced to extreme thinness, it appears by 

 transmitted light of a bright purple colour, very like the colour of iodine in its 

 gaseous state. 



EDINBURGH, December 21. 1842. 



