OPTICAL DEPORTMENT OF THE ATMOSPHERE 



IN EELATIOX TO 



PUTREFACTION AND INFECTION/ 

 11. 



§ 1. Introduction, 



An inquiry into the decomposition of vapours by light, 

 begun in 1868 and continued in 1869,^ in which it was 

 necessary to employ optically pure air, led me to experi- 

 ment on the floating matter of the atmosphere. A 

 brief section of a paper published in the Philosophical 

 Transactions for 1870^ is devoted to this subject. 



I at that time found that the air of London rooms, 

 which is always thick with motes, and also with matter 

 too fine to be described as motes, after it had been 

 filtered by passing it through densely packed cotton- 

 wool, or calcined by passing it through a red-hot pla- 

 tinum-tube containing a bundle of red-hot platinum 

 wires, or by carefully leading it over the top of a spirit- 

 lamp flame, showed, when examined by a concentrated 

 luminous beam, no trace of mechanically suspended 

 matter. The particular portion of space occupied by 

 such a beam was not to be distinguished from adjacent 

 space. 



The purely gaseous portion of our atmosphere was 

 thus shown to be incompetent to scatter light. 



1 Philosophical Transactions, Part I., 1876. 



2 Proc. Roy. Soc. vol. xvii. ^ Vol. clx. p. 337 



