Humidity: Effect of Heat upon Volume of Air. 15 



61. The absolute humidity of the atmosphere is much greatest in 

 summer, reaching its maxi- 

 mum iu July or August (0.5 

 to 0.6 inches), and its mini- 

 mum in December (0.1 or a 

 little higher). The relative 

 humidity follows a different 

 law, and through a much 

 less range. It ranges from 

 75 to 80 per cent in winter 

 in the Atlantic States, de- 

 scends to the lowest (about 

 65 per cent, on the general 

 average) in May, rises to 

 about 70 to 75 in the sum- 

 mer months, and a little 

 higher in winter. These 

 ranges of absolute and rela- 

 from 



5. Absolute Humidity at three American Sta- 

 tions through the several Months, for a Series of 



the mean of many years' ob- Years - 

 servation at the Magnetic 

 and Meteorological Observa- 

 tory at Toronto, in Canada, 

 and at the State Agricult- 

 ural Colleges at Orono, in 

 Maine, and at Lansing, in 

 Michigan, are shown by the 

 accompanying engravings. 



Effects of Heat and of Cold 

 upon the Volume of Air. 



62. It is a rule that heat 

 tends to expand all bodies, 

 whether solid, liquid, or gas- 

 eous, and that cooling tends 

 to reduce their volume. 



63. When any substance 



expands, it absorbs "latent 6. Relative Humidity at. three American Sta- 

 i , ?j j i ., tions through the several Months, for a Series of 



heat, and becomes colder. Years. 



