permanent Colours of Opake Bodies. 23.1 



Thus, when the air contained in a chamben 

 or in a court or area, is viewed through a giafs 

 window, the furface of the atmofphere, which is 

 contiguous to the glafs, refleds no colour, but 

 is pellucid and colourlefs. Noi is any colour 

 refledted by the furfaces of air, which are adja- 

 cent to water, cryftal, or any other media, placed 

 in contad with it. 



The air contains a great variety of extraneous 

 particles, which although they are alnnofl:, or 

 entirely, imperceptible when feparate, yet, when 

 viewed colledively, are capable of producing 

 vifible reflexions, by their united powers. 



When a beam of light is admitted through 

 a fmall hole, into a dark chamber, innumerable 

 motes are feen floating in the air, which is thus 

 illuminated. Thefe minute bodies vividly re- 

 flect a white light around them, in every direc- 

 tion, fo that they are diflinflly feen from every 

 part of the dark chamber. Such particles occupy- 

 all parts of the air which have been hitherto 

 obferved. 



The atmofphere abounds in volatile, and eva- 

 porable matters, which are difengaged from na- 

 tural bodies, by feveral operations, as fermenta- 

 tion, eflxrvefcence, putrefadion, the a£lion of 

 fire in volcanos, and various other means of de- 

 compofition. 



Many of the particles, which are feparated by 

 fuch procefles, differ confiderably, in denfity, 



0^4 from 



