228 



ABSOLUTE AND RELATIVE HUMIDITY. 



no different exposure to the sun than as due to changes of the seasons — 

 the ocean winds are much more regular than those from the land. It is 

 this regularity that renders the winds more reliable as a motive power, 

 in the neighborhood of the sea, than in the interior. It is to be further 

 noticed that we find in our country no prairies or treeless plains near 

 the sea, but always remote from its influences. Tbe effect of resistance 

 to an jierial current, is to condense the particles immediately in front of 

 the opposing body, and to create a partial vacuum immediately behind 

 it. Uuder these opposite influences the temperatures are correspond- 

 ingly aflected, and with them the hygrometrical conditions, so that high 

 mountain peaks are sometimes capped with clouds, when the sky is 

 otherwise clear, and these clouds clinging to the peaks, although a strong 

 wind may be blowing. 



The curve of relative humidity is considerably less at Brussels than 

 at St. Petersbursr, with its maximum in January and its minimum in 

 May. That of Sitka, which is much higher than the rest, is lowest in 

 April and May and highest in August and September. The other sta- 

 tions differ, as will be more apparent on careful study.^ 



Observations upon humidity have been made without interruption or 

 change of plan, and with unquestionable care, at the Toronto Magnetic 

 and Meteorological Observatory, since 1854. We have an eight-year series 

 in Maine, at the State College of Agriculture and the Mechanic Arts at 

 Orono, and one of fourteen years at the Michigan State Agricultural 

 College at Lansing. Although one of these stations is across the bor- 

 der, it may be taken to represent the hygrometrical conditions that 

 exist in that region, which are probably not much, if any, different from 

 those across the lake; and a comparison of these results will serve to 

 show the general laws which govern in the monthly average, and through 

 a term of years, the variations in relative humidity and pressure of vapor 

 throughout the several seasons of the year. 



Hygrometrical ohservations at Toronto by months since 1854. 



(a.)-MEA-N- ABSOLUTE HUMIDITY. 



(&.)-MEAN RELATIVE HUMIDITY. (Saturation=1.00.) 



' In the sonthern hemisphere these curves are reversed, the maxima and minima 

 coming like their seasons, at the opposite months, and subject to laws not of intenst in 

 the present inquiry. 



