ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 323 



of air and ground. The emission of organic particles from marshes 

 and drying edges of pools, etc. 



The amount of organic matter and number of microbes in the air in 

 different situations, hours, and seasons, as, for instance, in malarious 

 valleys and tracts, and on hills and house tops compared with a height 

 of 3 or 4 feet from the ground, on sandy malarious plains on still even- 

 ings, in places subject to cholera, diarrhea, and rheumatism, in low 

 meadows and by river banks at sunset in summer, in places some miles 

 to windward and to leeward of great towns, in streets, in old and new 

 houses, in crowded places, in railway cars and in cabins, and in schools. 



An investigation of all the phenomena and physics of evaporation 

 from liquid and solid surfaces. The development of electricity, the 

 effects of differences of temperature, of surface tension of slight 

 impurity and slight films of oily matter, the phenomena of the dust- 

 free envelope, and the conditions of evaporation from the human body 

 would be within the scope of the inquiry. 



The determination of the resisting power (1) in pure fresh air, and 

 (2) in foul or rebreathed air in a room, of the various microbes con- 

 cerned in various diseases of an infectious nature. The effect of dry- 

 ness of air, of sunshine, of the presence of a minute trace of organic 

 matter, of the character of the material, whether mineral or organic, 

 on which they rest. The effect of ozone, of nascent oxygen, and of the 

 vapors of various antiseptic or "disinfecting" substances. The capa- 

 bility of growth of various disease microbes on culture material 

 intended to imitate the organically contaminated walls or rooms, etc., 

 and the discovery of means for preventing such growth and emission 

 into the air of inhabited places. Examination and culture of microbes 

 and experiment on microbes found on walls of closely inhabited rooms. 

 Cultivation of microbes on size used for papering, and on paper, and on 

 plaster. The observation of the number of microbes in air over vari- 

 ous kinds of street pavement. Examination of systems by which the 

 air of sewers and drains may be prevented from entering dwelling 

 houses, and of means by which the drain may enter the sewer from 

 underneath, so that the drain may effectually and permanently be 

 sealed by contained water or sewage. 



A very interesting branch of research, and one to which little atten- 

 tion has hitherto been paid, is the formation of ice crystals, snow, and 

 hail. In the free atmosphere, beautiful crystals develop themselves in 

 great variety, mostly hexagonal or six-rayed, but some few with three 

 or twelve rays, and some of less regular shape. At least two hundred 

 different shaped crystals have been observed and drawn, many of the 

 most exquisite delicacy and regularity. Often a single shower yields 

 several different species of snow crystals, but generally there is great 

 similarity in the crystals which fall about the same time. The cause of 

 the difference in shape has not been made out, and indeed is not likely 

 to be fully accounted for by any means at our disposal, but the present 



