322 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



column of air above it, and the rise, in most cases, is simply explained 

 by the condensation of vapor permitting drier air to flow in, and still 

 more by the existence of a cold, heavy mass of air at some rather high 

 altitude, which, indeed, is one of the main causes of the storm. The 

 barometer may very probably in most thunder or hail storms be acted 

 upon oppositely by the two coexisting conditions, a humid column of 

 ascending air and a descending block of upper air colder than the 

 average of its level. Hence the mercury is either stationary or oscil- 

 lates within narrow limits. The rise under the ascensional column may 

 also be frequently caused by the rapid ascent of a column of air which 

 takes an appreciable time to expand to the lower density of the upper 

 levels. A study of the temperature and barometric movements before 

 storms of different kinds, and with different winds, might lead to a use- 

 ful prognosis of the course and character of storms, tornadoes, and 

 heavy rains. 



Observations on the rate of change of ocean temperatures at differ- 

 ent depths in relation to the temperature of the air and to the influence 

 of currents are needed, and also of the rate of cooling and warming of 

 air currents passing over a sea surface of lower or higher temperature. 



Experiment is needed in extension of our knowledge respecting the 

 amount of ground air and gases in various soils, their expansion under 

 variations of atmospheric and ground temperatures, of atmospheric 

 pressure, and of natural processes of decomposition. Smoking or 

 scented substances buried in the ground might afford some useful 

 information. Also, respecting the production of gases by bacteria in 

 the soil, the movements and permeation of ground air or gases through 

 various soils, the emission of microbes into the air at different seasons 

 and hours, and the density of microbes in the air near the ground. 

 Also, respecting the depth in various soils at which organic matter 

 best undergoes harmless decomposition, so as not to give out noxious 

 products to the air to a degree dangerous to health, or offensively, so 

 as not to poison wells, and so as to be of maximum benefit in agricul- 

 ture. The relations of ground air to the ground water. 



The amount of dew derived from the earth, directly, in various tem- 

 peratures, soils, and circumstances; the amount exhaled by various 

 plants, and the amount of organic matter and microorganic life in dew 

 in particular situations, such as malarious tracts and water courses. 

 The depth from which dew may be derived, as, for instance, the meas- 

 urement of the depth at which the soil begins to be moist on sandy 

 elevated malarious plateaus, where dew vapor emanates from the 

 ground, but the surface down to several inches is dry. 



The discovery of some means of determining the amount of moisture 

 belonging to dew proper and to deposition from very humid air on 

 solids in certain states of the atmosphere. 



The emission of solid exceedingly minute particles from wet evapo- 

 rating and drying earthy and other surfaces at different temperatures 



