VOL. XLV.] PHILOSOPHICAL TRANSACTIONS. 515 



The mean heat of the shaded air, in spring, summer, autumn, and winter, 

 taken from the mean nocturnal heat, and from the mean heat at 2 or 3 p. m. is 

 61, 78, 715 and 51 degrees. 



The mean heat of the shaded air at 2 or 3 p. m. in spring, summer, autumn, 

 and winter, is 65, 82, 73, 55 degrees; and the mean nocturnal heat in these 

 seasons is 37, 74, 68, and 49 degrees. Therefore our winter's nocturnal heat, 

 at a medium, coincides nearly with the temperate heat in England. 



The thermometer, when suspended 5 feet from the ground, and exposed to 

 the direct rays of the sun, and to those reflected from our sandy streets, has 

 frequently rose in a few minutes, from 15 to 26 degrees, above what was at that 

 time the heat of the shaded air. When we are therefore exposed in the streets 

 to the sun in summer, we inspire air from 4 to 28 degrees warmer than the heat 

 of the human body. 



The thermometer, when buried in the sands of the streets, when the heat of 

 the shaded air was 88, rose in 5 minutes to 108, though there was at the same 

 time a moderate wind. 



In June 1738, when the heat of the shaded air was gs, the thermometer sunk. 

 1 degree in his arm-pits; but continued at 98 in his hand and mouth; from 

 which we see what little concern the air has in cooling the blood in the lungs. 

 Two men who were then in the sti-eets, when the heat was probably 124 or 126 

 degrees, (as the shaded air's heat was then 98) dropped suddenly dead ; and several 

 slaves in the country, at work in the rice fields, shared the same fate. Dr. Ij. 

 saw one of the men immediately after he died; his face, neck, breast, and 

 hands, were livid. 



From the barometrical table it appears, that the barometer's mean altitude, 

 taken from its greatest and least height, is 30.09 inches; and that its range is 

 only 1.22 inch. Therefore their atmosphere varies only -^ part in its weight. 

 In the warm months, the mean barometrical station, taken from its greatest 

 and least altitudes in these months, is 30.09 inches; and he never saw its range 

 in these months exceed -,^5- parts of an inch ; therefore the changes of their at- 

 mosphere's weight, in the warm months, will have but little effect on human 

 constitutions, as the difference between its greatest and least pressure is but 

 part of that in cold climates, where the range of the barometer is 3 inches 

 May not the great height of the barometer in the warm months in this climate, 

 proceed from the vast quantity of water, which is at that time supported in the 

 atmosphere, as the exhalation is then very great? or may it not proceed from the 

 rarefaction of the mercury? for the weight of the mercurial column, at equal 

 altitudes, will be different under different degrees of heat; and the mercury may 

 therefore be supported at equal heights by columns of air of unequal weights. 



3u 2 



T 



