3H 



POPULAR SCIENCE MONTHLY. 



is indicated by the shaded areas. It can be observed how the winds 

 blow with the hands of a watch around the high, which is central over 

 JSTew Mexico, and in the opposite direction about the low, which is 

 central over Sault Ste. Marie. The temperature is higher to the east 

 of the low, and falls behind the low and before the high in their 

 eastward progress. The rain is seen accompanying the low and to 

 the east of it. 



For the purposes of forecasting it is necessary to know the baro- 

 metric pressure, direction of the wind, and state of the skies. All this 

 information is telegraphed to the Weather Bureau twice daily from 



Fig. 7. — The Thermograph. 



each of the stations of observation, and all other telegraphic business 

 must give way to this for the time being. Each message is, by means 

 of a cipher, usually expressed in ten words or less. The observations 

 are taken at 8 a. m. and 8 p. m.. Eastern time. The results are ex- 

 changed with the Canadian Weather Bureau. The principal stations 

 are provided with recording instruments, so that a continual record 

 is kept of all these features of the weather. While the instruments 

 appear complicated, they are based on principles that are easy of com- 

 prehension. 



The barograph consists of a series of corrugated sheet-metal 



