MISCONCEPTIONS CONCERNING TEE WEATHER 137 



respiration is concerned, because of the diurnal change in relative 

 humidity, the change usually being inversely as the temperature. The 

 actual amount present, however, does not change greatly from day to 

 night. If therefore, night air is dangerous for convalescents, and it 

 probably is not, it is because of physical and not chemical differences 

 between it and day air. 



The importance of ozone as a constituent of the atmosphere is 

 popularly overestimated, and the numerous advertisements referring 

 to it as the basis of the health-giving qualities of the air at certain 

 resorts are largely a delusion and a snare. In a molecule of ozone, one 

 of the allotropic forms of oxygen, three atoms of oxygen are held 

 together in such a way that there is but feeble chemical attraction of 

 two atoms for the third atom, which readily leaves the other two to form 

 a compound with some other element. It is because of the latter char- 

 acteristic that ozone has its peculiar properties. Though there is con- 

 siderable diurnal and annual range in the amount present in the 

 atmosphere, and also a large difference between that of the air in cities 

 and that in the country or in the free air, the relative proportion, in 

 general, is but one part in a million. In nature it may be formed (1) 

 by lightning discharges, thus explaining the unusual odor sometimes 

 perceptible immediately after a thunderstorm, (2) by the evaporation 

 of water, particularly in clouds or near waterfalls and fountains, and 

 (3) the action of ultra-violet light upon oxygen, probably most effective 

 in the free air above the highest cloud level. However, the healthful 

 properties of the air at various resorts is due primarily to the dryness 

 of the air, the relatively low temperature with small diurnal and annual 

 ranges, the absence of dust and smoke, and the increased amount of 

 atmospheric electricity, and only secondarily to the larger amount of 

 ozone present in the atmosphere. 



Since the sun is ultimately the source of all the heat of the atmos- 

 phere the question is sometimes raised: "Why is not the upper air, 

 being nearer the sun during the day, warmer than the lower air, 

 which is more distant; in other words, why is there not an increase 

 rather than a decrease in temperature with height ? " Eecords obtained 

 by means of kites and balloons show, among other things, (1) that up 

 to a height of about 6 miles there is a more or less uniform decrease of 

 temperature with height, (3) that the density of the atmosphere de- 

 creases rapidly with height, it being half as dense at a height of 3.5 

 miles as it is at sea level, and (3) that the water vapor is limited to the 

 lower strata, 80 per cent, of it being below a height of 3 miles. The 

 last two conditions explain the first. Partly because of the adiabatic 

 rate of decrease of temperature of a gas with a decrease of its density, 

 and partly because of the ability of water vapor to remove and to store 



VOL. LXXXVI. — 10. 



