24 IMPOTENCE OF AIR. 



deposited upon the sides of the chamber as well as 

 upon the floor. " The chamber was examined almost 

 daily ; a perceptible diminution of the floating matter 

 being noticed on each occasion. At the end of a week 

 the chamber was optically empty, exhibiting no trace 

 of matter competent to scatter the light." This ex- 

 periment is calculated to convince any one who doubts 

 the fact that particles of lifeless matter, even when 

 very minute, really do tend to fall through air, until 

 they reach some resting place which prevents them 

 from falling still lower, and the great discovery is 

 announced that ponderable bodies are ponderable. 

 But the demonstration determines nothing whatever 

 with regard to living particles, not even their pre- 

 sence. 



Dr. Tyndall also makes a prediction 'concerning the 

 discovery of the cause of the impotence of certain 

 air as a " generator of life," as if air, which is lifeless, 

 could under any circumstances generate that matter 

 which lives. Has any one been educated into a belief 

 in the life-generating properties of the air ? 



The nature of the materials which make up the 

 dust of our air is a subject which has often engaged 

 the attention of microscopists, who have long been 

 familiar with the fact that multitudes of organic par- 

 ticles derived from various sources are floating in the 

 more or less disturbed air of our rooms. Many of 

 these fall into our microscopic specimens while they 

 are being mounted,, and in spite of all our care, and 



