ATMOSPHEEE IN RELATION TO HUMAN LIFE AND HEALTH. 339 



fact is fully proved, and clouds and fogs often seem to be still liquid at 

 12° to 20° F. below the ordinary freezing temperature of large drops. 

 But the degree of cooling which may be borne without freezing, and its 

 dependence upon the size of the globules in the free air, has yet to be 

 determined. Observation of the sun and moon and the diffraction 

 effects in clouds at ascertained heights would be the best available 

 means, short of direct observation at great heights, of fixing the rela- 

 tion of size to congelation at various temperatures. 



DISTRIBUTION OF VAPOR CLOUDS. 



Experiments with kites and with electrometers have shown that 

 transparent vapor is grouped in masses through the air like visible 

 clouds, but less continuous, and astronomical observations seemed to 

 show a distribution of the atmosphere not only into horizontal strata, 

 but into vertically extended compartments differing greatly from each 

 other. Brief perturbations of polarization, occurring at any hour of the 

 day, have been ascribed to " clouds " of cirrus, etc., too faint to be seen. 

 Becent experiments in the foehn and in other hill and valley winds have 

 shown considerable differences of temperature at intervals of a few 

 minutes. Delicate and sensitive thermometers, hygrometers, and elec- 

 trometers might well be used for the further discovery of the varying 

 states and divisions of the air in respect of temperature, humidity, and 

 electric state and of the causes of differences. 



There is much reason to assume that the atmosphere is divided, like 

 the sea, into many large and small masses of unequal temperature. 

 The great reluctance of waters of different temperatures to mingle, as 

 seen in the neighborhood of Newfoundland and of the Gulf Stream, 

 also at the head of the Lake of Geneva where the Bhone enters, and 

 at the junction of the Bhone and Arve below Geneva, has its counter- 

 part in the atmosphere. It is curious to see a large body of water like 

 the Bhone plunge down toward the bottom of the lake, leaving only 

 floating substances on the surface. 



The present author believes that since particles of water in the air a 

 little smaller than those of fine blue haze would be quite invisible, 

 owing to their inability to reflect light, like a soap film a millionth 

 of an inch thick, which is quite invisible, there must be a quantity of 

 water in moist, transparent air which is competent to arrest heat waves 

 by absorption, and is not in the state of vapor. He believes that a 

 theoretical and experimental investigation of the various conditions of 

 vapor and water in the air would lead to interesting and important 

 results. The effect of a thin veil of cirrus, and of a slight, equally dis- 

 tributed haze upon the intensity of solar radiation has been recently 

 investigated at Catania and Oasa del Bosco (4,725 feet above the sea). 

 The cirrus was found capable of intercepting 30 per cent of the radiant 

 solar energy. The haze intercepted 23 per cent when the sun was 10 



