S38 EPOCHS IN THE HISTORY OF THE CONTEMPLATION OF 



our atmosphere may turn daily round the Earth like the 

 heavens, and may thus occasion the East wind/'' 



Hooke's comprehensive genius acted here also as the 

 restorer of light and order. ( 522 ) He recognised the influence 

 of the Earth's rotation, as well as the existence of upper and 

 lower currents of warm and cold air, passing from the 

 equator to the poles, and returning from the poles to the 

 equator. Galileo, in his last Dialogo, had indeed also 

 considered the trade winds as a result of the Earth's rotation ; 

 but he ascribed the remaining behind of the particles of air 

 within the tropics to a vapourless purity of the air in those 

 regions. ( 523 ) Hookers juster view was not revived until 

 the 18th century, when it was again put forward by Halley, 

 and explained more circumstantially and satisfactorily in 

 Tegard to the operation of the velocity of rotation proper to 

 each parallel of latitude. Halley had been previously led 

 by his long sojourn in the torrid zone to publish an excellent 

 work on the geographical extension of the trade winds and 

 monsoons. It is surprising that in his magnetic expeditions 

 lie makes no mention of the " law of the winds" so 

 important for the whole of meteorology, as its general 

 features had been recognised by Bacon, and by Johannes 

 Christian Sturm of Hippolstein, who, according to Brewster, 

 ( 524 ) was the true discoverer of the differential thermometer. 

 In the brilliant period of the foundation of (C mathematical 

 natural philosophy," attempts to investigate the moisture of 

 ihe atmosphere in its connection with variations of tempera- 

 ture, and with the direction of the wind, were not' wanting. 

 !The Academia del Cimento conceived the happy idea of 

 cbtermining the quantity of vapour by evaporation and 



