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have killed young plants of Indian corn at 48^ and have been known at 54*^. Black froft, and even ice, have been produced at 38t°, which is 64- degrees above the freezing point. That other circuftances muft be combined with the cold to produce froft, is evident from this alfo, on the higher parts of moun- tains, where it is abfolutely colder than in the plains on which they ftand, frofts do not appear fo early by a confiderable fpace of time in autumn, and go off fooner in the fpring, than in the plains. I have known frofts fo fevere as to kill the hiccory trees round about Monticello and yet not injure the tender fruit bloffbms then in [ ^55 ] bloom on the top and higher parts of the mountain; and in the courfe of 40 years, during which it had been fettled, there have been but two inftances of a general lofs of fruit on it: while, in the circum- jacent country, the fruit has efcaped but twice in the laft feven years. The plants of tobacco, which grow from the roots of thofe which have been cut off in the fummer, are frequently green here at Chriftmas. This privilege againft the froft is undoubtedly combined with the want of dew on the mountains. That the dew is very rare on