Kew Oullines of Chemical Philosophy , 433 



ness or cloudiness of the ?ky, as the nocturnal variations were. 

 In the month of September, \A-hen the glasses rose from 60° to 

 70', tlie heat at the lower station constantly exceeclcil the heat 

 at the Ujipcr station ; and in some measure proportionably, as 

 the weather was hotter*. 



" Tiiat the clearness of the sky should contribute to the cool- 

 ness of the air in the night, is not at all surprising ; but that, 

 whenever tlie skv becomes clear, the cojd sliould seem to arise 

 from the earth, and be found in the greatest degree, as long as 

 it continues clear, in the lowest situation, seems a little extraor- 

 dinary : this however seemed to be the case, both in the warmei: 

 and in the colder weather, daring the uhole time these observa- 

 tions were taken. About noon, on the 3d of .January, the sky 

 becoming clear, the air get cooler ; and going into my garden 

 about eight in tiie evening, I perceived the surface of the ground, 

 v,'hich had been wet bv the rain in the forenoon, begin to be 

 frozen. Looking immediately at the thermometer, I saw the 

 mercurv at 33 f" ; and observing a i)iece of wet linen hanging 

 near the ghiss, not live feet from the ground, I took it into my 

 hand, and found it not in the least frozen ; by which it ap- 

 peared, that the degree of cold which had frozen the surface of 

 the ground, had not then ascended to the glass, nor to the linen, 

 and consequently had not been communicated to the air five or 

 six feet above the earth. The next day I found, as expected, a 

 consideraljlc local variation ; the index for the cold of the ni^ht 

 in the garden Ijciiig at 32', that on the hill being 3.51", and tluit 

 on the top of t'le town at 37 1^ Probably the weather did not 

 continue clear the whole iiight: if it had, it is likely the degree 

 of cold would have been found proportionably greater at every 

 station. On the morning of the 4th, there fell a misty rain, 

 which continued only till noon, when the sky became clear 

 again, and continued so till the 7th ; during which time the 

 nocturnal heights of the thermometers differed considerably 

 from each other ; but on the sky's becoming cloudy, the local 

 variation ceased f." 



To confirm in a more particular manner the foregoing oljser- 

 vations respecting a remarkable refrigeration, which in dear 

 weather takes place in the night near the earth's surface, Mr. 

 Six continued his journal, with the omission of a few days only, 

 from July 1784 till July 1783. 



* " As the lioat at tlic lower station exceeded the heat at the upper ones, 

 when the weather was hot; and etprally so, when the sky was cloudy, as 

 well as wl)cn it was clear; it appears, 'that the glass at th(* lower station 

 was not materially alTcctcd hy the reflection ol" the sun's r.nys from th« 

 earth, as at first I apprehended it %voulcl be." 



t I'Lil. Trans, abr. vol. xv. p. C09. 



Ee4 



