38 



It is also very useful in forecasting the weather, and will frequently indicate a eominpr change » 

 day or two in advance of the barometer. For this purpose it resembles, in some respects, the «.n-band 

 spectrorcope. in a coming change of weather, before even the th.n streaks of cirrus cloud appear 

 across the skv, it is known that the amount of aqueous vapour present h,gh up in the atmosphere 

 increases in quantity, and this increase is shown in the spectroscope by the more prominent absorbt.on 



ines known Is the rain-band. This vapour also acts like a great blanket or covenng. and prevents 

 the heat of the earth from radiaUng into space. After a little experience with the mstrument one 

 can tell whether the amount of aqueous vapour is increasing or decreasing, and <S° thereby forecast 

 with considerable accuracy, the nature of the weather that may be expected. .J^l^f^ll'l^^J^i 

 open one, the whole length of the instrument representing only about twelve degrees instead of the 



120- or 130" usual in thermometers, and it is deeply engraved on zinc so that it will stand the action 

 of the weather without dete.ioration. It may be hung on a north wall or exposed on the grass, but 

 it should, it possible, be protected from the direct solar rays. 



«^^ SUNDAY 



3 6 9 N .^ 

 <^f MONDAY 



Ji...: 

 <^ N 3 6 9 



r TUESDAY 



-^t^ZT^ 



3 ^ 9N» egfti 

 ■ WEDNESDAY 



