DISTRIBUTION OF TEMPERATURE ON THE EARTH. 223 
duce as a second cause the fact that the masses of air previously 
in a state of rest are set in motion one after the other,—and that 
thus the point of commencement of the current, which in Had- 
ley’s theory is invariable, here becomes continuously variable,— 
and if we extend this view to two currents of wind in continual 
conflict, we deduce immediately the ‘ Law of Rotation, and at 
the same time the laws for the motion of the instruments, as I 
have shown in the Fourth Part of my ‘ Meteorological Researches.’ 
That, however, which is seen in the movements of our instruments 
at one place will, of course, become more strikingly apparent 
when the simultaneous diffusion of the phanomena oyer a 
greater extent of the terrestrial surface is laid before our eyes: 
the force, direction, and conflict of the two opposing currents 
will then become more evident. 
Supposing that, at a certain time, a modification in the mean 
distribution of temperature is caused by these currents, if we 
proceed in the direction of their course we shall everywhere find 
either a rise or a fall relatively to the normal temperature ; if, 
however, we proceed more or less perpendicularly to this direc- 
tion, we shall somewhere find their line of separation. 
In this work the thermal phanomena for the last fifty years 
have been compared. Observations at one place, or for single 
years, can never be of any very great importance ; the results are 
often erroneous when obtained from such sources. 
; Observations from fifty-nine places have been employed, 
__ twenty-two in Germany, twelve in England, six in North Ame- 
rica, five in Italy, three in Switzerland, three in Sweden, two in 
Holland, two in Russia, one in Hindoostan, one in Iceland, one 
in France, and one in Siberia. 
(Then follow tables showing the mean temperature of the 
twelve months in these fifty-nine places, calculated for several 
years. As example, the temperature of the year 1836 is here 
drawn from the several tables.) 
Boston (Fahrenheit), 1826-1839. 
Jan, Feb. | March. | April.| May. | June. | July. | Aug. | Sept. | Oct. 
836) 37°3 |375 |42:7 | 45°8| 54-8 | 62°4 | 62-1 | 59°6 | 54-9 48-0 414 
38:9 
