500 



POPULAR SCIENCE MONTHLY. 



account for all the facts that have been noted in a simple and natural 

 manner. 



The most important use of the cloud observations is not the study 

 of their constitution, but of their motions relatively to the surface of 

 the earth. A cloud is a meteorological meteor, and moves in the 

 stratum of air at approximately the same velocity as the atmosphere 

 itself, so that a measurement of its direction and velocity gives that of 

 the air current, just as a chip floating on a stream shows how fast the 

 water is running. Repeated measures of this kind, when classified, 

 teach us that the atmosphere flows with certain typical movements, and 

 that by them the laws controlling its average circulation can be deter- 



Chart 4. Storm in the Lake Region, a winter cyclone or low area. 



mined. Now it is a fact that because meteorologists could observe the 

 motions of the wind readily at the surface of the earth, but not in the 

 upper strata of the air, they have relied too much upon conjecture in 

 constructing the theories of the constitution of storms. The mathe- 

 matical analysis has had therefore only an imperfect basis upon which 

 to rest, and consequently it has made slow progress towards a complete 

 solution of the problem. The international observations on clouds, 

 during the year May, 1896-July, 1897, had for their immediate object 

 the accurate determination of the motions of the upper air, with a 

 view of testing the existing theories, and constructing new ones wher- 

 ever necessary. This period of scientific observation is similar to the 

 Tycho Brahe and Kepler stage of astronomy, when observations of the 

 motions of the planets were accumulated for the use of the coming 



