ARISING FROM DIFFERENCE OF LATITUDE. 15 



On looking over the tul)le, we can liaiclly fail to notice the slower rate of decrease in 

 temperature as we rise from the vallej- of the Mohawk, than in other parts of the State ; 

 occasioned probably by the greater prevalence of northwest winds in that valley, which 

 tend to reduce its temperature. In the foritier it averages but 1° in 581 feet ; while in 

 the latter, it is 1° in 304 feet. The mean of all the observations compared gives 1° for 

 every 372 feet ; but making some allowance for the slow rate in the valley of the Mo- 

 hawk, I shall assume it at 1° in 350 feet. This result does not differ materially from 

 that which w^as obtained from observations taken in balloons and on mountain heights, 

 though it would seem from philosophical considerations thai tlune should be a difference. 



In regard to the influence of difference of latitude on temperature, we know that the 

 mean annual temperature is greatest near the equator and least toward the poles. If we 

 regard the difference between the equatorial and polar temperatures as the amount due to 

 the sun's influence, Mr. Kirw^an found that in mid-ocean this is always nearly proportional 

 to the square of the cosine of the latitude of the place ; and in accordance with this law, 

 he calculated a table showing the temperature due to all latitudes. In latitudes varying 

 from 30° to 50^, he makes the temperature diminish about 1% of a degree for each degree 

 of latitude. This, it must be recollected, is intended as the rule on the ocean, remote 

 from either continent. Observations show that such an allowance is too small in Europe, 

 and much more so in this country, where a given change of latitude affects the climate 

 more than it does there. 



To find the law in this country, particularly in our own latitude, I compared the tempe- 

 rature of places along the Hudson river, together with Cambridge and Plattsburgh. I 

 selected these places, because, with the exception of difference of latitude, the general 

 circumstances which affect the climate are very similar in them all. They all lie in val- 

 leys extending in a north and south direction ; are all nearly on the same level, except 

 Cambridge ; and the character of the winds is verj' similar in them all.* The observations 

 at all these places were taken between the years 1826 and 1842, but not all during the 

 same years. It was therefore necessary, in order to compare them properly, to seek for 

 some place where they had been taken during the whole period without interruption, that 

 I might know whether the mean temperature of the years observed at any particular place 

 was higher or lower than the general average. I selected the observations at Albany as 

 such a standard of reference. Its central position in regard to the other places, as well as 

 the care with which the observations there are known to have been taken, seemed a valid 

 reason for doing so. . ~ 



I next proceeded to compare the mean temperature of each of the places selected, with 

 that of Albany during the same years, and the latter with its mean temperature for the 

 whole seventeen years, varying that of the place compared by the same amoimt. I then 

 reduced the temperature of all to the level of the sea, by allowing 1° for every 350 feet of 



' See article on the winds of the Slate, published in the Regents' Report for 1840. 



