296 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
THE CONSTITUTION AND PROPERTIES OF THE ATMOSPHERE. 
To the chemists and physicists meteorologists owe a long series of 
researches on the constitution and properties of the atmospheric gases. 
This work may be said to have begun with Boyle next after the less 
important work of European alchemists. Galileo had shown that the 
air has weight. Otto von Guericke had so constructed his first air 
pump (as shown by the pictures, although he himself does not say 
so in words), that the heavy air should flow down and out of the 
vessels from which he would pump it as he pumped water. But it is 
to Boyle that we owe the idea that there is an elastic spring in the air, 
and also that the air is a complex combination of several different 
vapors, such as those that produce rust and those that are exhaled 
from the earth, the water, vegetables, and animals. Indeed, the 
springiness of the air excited his suspicion that there might be some 
vital substance diffused through the atmosphere. The experiments 
that he proposed to have made—that he in fact began, and that were 
carried out by his contemporary, John Mayow—bore on respiration, 
oxidation, and evaporation as the sources of new kinds of air. 
Boyle was the first to suggest that the atmosphere consisted of 
air, properly so called, and water in a state of expansion, together 
with other gases that emanate from the earth and exert an injurious 
influence on the health. De Saussure seems to have been the first 
to measure the absolute quantity of aqueous vapor in a given volume 
of atmosphere. In 1760 Lord Cavendish showed that the vapor 
evaporating from water in a vacuum had a definite elastic pressure, 
which he measured at several different temperatures. 
The temperature of the dew point seems to have been first ob- 
served by Le Roy (1750), Dalton (1800), and Daniel (1820). The 
psychrometer, or wet and dry bulb thermometer, is generally ascribed 
to August (1825), but the wet bulb was used long before by Beaumé; 
it was August who gave us an acceptable, rational theory of its 
action, while at the same time, and quite independently, Ivory in 
1822, Espy in 1829, Belli in 1830, and Apjohn in 1834, introduced 
modifications, all of which are now combined in Ferrel’s, Grassman’s, 
and other theories and tables for the whirled psychrometer. The 
relative humidity was first observed by means of a catgut hygrom- 
eter by Brander (1650), but the hair hygrometer of De Saussure 
(1780) and his persistent researches to improve it were the first 
steps in modern hygrometry. 
The discovery of carbonic-acid gas, or fixed air, is generally at- 
tributed to Joseph Black, of Edinburgh, who, however, had several 
predecessors less widely known. In 1752 he discovered that this 
gas is the same as choke damp, or fixed air. According to Ramsey, 
Black showed that the common air of the atmosphere contains a 
