40 On the supposed Change 



greatest cold at Ratisbon, by a series of observations, to 

 be 13° 45 below cipher by Farenheit, and the mean of 

 the greatest colds, 2° 42 JdcIow cipher. At Manheim, 

 the greatest cold was 8° 95 below 0, and the greatest 

 mean of cold 1° 2 above 0. From all which it is obvi- 

 ous that no diminution of cold, equal to 16 degrees, can 

 have taken place, since the Goths and Vandals invaded 

 the Roman empire, as Dr. Williams supposes ; for the 

 cold which reduces the mercury by Farenheit's scale to 

 8 or 10 degrees above cipher, if continued only two or 

 three days, must cover the Rhine and Danube with so- 

 lid ice. 



Before I conclude this subject, it is proper to notice 

 what Mr. Jefferson has written on the climate of Vir- 

 ginia.... Ao^e^, Qiiey-y 7. " A change in our climate," 

 says this author, " is taking place very sensibly. Both 

 heats and colds are become much more moderate, with- 

 in the memory even of the middle aged. Snows are 

 less frequent and less deep. They do not often lie be- 

 low the mountains more than one, two or three days, 

 and very rarely a week. The elderly inform me, the 

 earth used to be covered with snow about three months 

 in every year. The rivers which then seldom failed to 

 freeze over in the course of the winter, scarcely ever do 

 so now. This change has produced an unfortunate fluc- 

 tuation between heat and cold in the spring of the year, 

 which is fatal to fruits." 



What evidence there is of a diminution of heat in 

 summer, I do not know ; but I find abundant evidence 

 that no such diminution has taken place. And that no 

 very definite proof of the fact has appeared, is very ob- 

 vious from the difference of opinion on the subject. Mr. 

 Jefferson supposes a diminution of the heat of summer. 

 Dr. Williams supposes a general increase of heat in 

 our climate ; and I leave them to adjust the difference 

 between themselves. 



Mr. Jefferson seems to have no authority for his opin- 

 ions but the observations of elderly and middle-aged 

 people. But what shall we say to the following facts ? 

 Mr. Jefferson informs that in Virginia, the snow used to 

 cover the earth about three months in every year. How 



