HAS OUR CLIMATE CHANGED? 



671 



locality at which the observation is made. The former represents the 

 quantity of heat over a long line, including many localities. It is, 

 therefore, the better form, and furnishes more trustworthy results. 



Turning now to the records of the city of New York, as obtained 

 from the sources above specified, we find they are continuous from 

 1821 to the present time. It would extend this report unduly were 

 we to enter on an examination of each of these years respectively. 

 Making a selection, then, let us compare the following groups of five 

 years first, from 1821 to 1827; second, from 1831 to 1837; third, 

 from 1841 to 1847; fourth, from 18G6 to 1872. It will be understood 

 that the months selected are January, February, and March. 



TABLE, SHOWING THE MEAN TEMPERATURE IN NEW YORK, FOR THE FIRST THREE 

 MONTHS OF THE YEAR, JANUARY, FEBRUARY, AND MARCH. 



The mean for January, February, and March, for thirty- three years, 

 is 32.90 degrees. The mean for the above selection is 33. 06 degrees. 



The evidence thus derived from thermometric observations cor- 

 roborates that derived from the freezing of the river, and undeniably 

 leads to the conclusion that, if there has been any change in the winter 

 climate of New York, it cannot be demonstrated by the extant thernio- 

 metrical records of the last fifty years. This, therefore, adds weight 

 to Humboldt's conclusion that there has been no sensible change in 

 the Atlantic States since the time of their first settlement. 



Let us next see what is the evidence afforded by an examination 

 of the Philadelphia records. As in the preceding case, a discussion 

 of all these would be too lengthy. They go as far back as 1748, but 

 present, however, a broken series. Selecting from this, here and there, 

 periods of five years, we may thus group them: first, from 1766 to 

 1772; second, from 1797 to 1803; third, from 1821 to 1827; fourth, 

 from 1831 to 1837 ; fifth, from 1851 to 1857. 



TABLE, SnOWINO THE MEAN TEMPERATURE OF PHILADELPHIA, FOR THE FIRST 

 THREE MONTHS OF THE YEAR, JANUARY, FEBRUARY, AND MARCH. 



