FUNCTION.] HALES UN PERSPIRATION. 289 



pot, I found the greatest perspiration of twelve hours in a 

 very warm dry day, to be one pound fourteen ounces; the 

 middle rate of perspiration, one pound four ounces. The 

 perspiration of a dry warm night, without any sensible dew, 

 was about three ounces ; but when any sensible, though small 

 dew, then the perspiration was nothing ; and when a large 

 dew, or some little rain in the night, the plant and pot were 

 increased in weight two or three ounces. N.B. The weights 

 I made use of were avoirdupoise weights. I cut off all the 

 leaves of this plant, and laid them in five several parcels, 

 according to their several sizes, and then measured the sur- 

 face of a leaf of each parcel, by laying over it a large lattice 

 made with threads, in which the little squares were half of 

 an inch each ; by numbering of which I had the surface of 

 the leaves in square inches, which, multiplied by the number 

 of the leaves in the corresponding parcels, gave me the area 

 of all the leaves ; by which means I found the surface of the 

 whole plant, above ground, to be equal to 5616 square inches, 

 or 39 square feet. 



I dug up another Sunflower, nearly of the same size, 

 which had eight main roots, reaching fifteen inches deep and 

 sideways from the stem. It had besides a very thick bush 

 of lateral roots, from the eight main roots, which extended 

 every way in a hemisphere, about nine inches from the stem 

 and main roots. 



In order to get an estimate of the length of all the roots, 

 I took one of the main roots with its laterals, and measured 

 and weighed them, and then weighed the other seven roots, 

 with their laterals, by which means I found the sum of the 

 length of all the roots to be no less than 1448 feet. 



And supposing the periphery of these roots at a medium, 

 to be -fg- of an inch, then their surface will be 2286 square 

 inches, or 15 '8 square feet; that is, equal to of the surface 

 of the plant above ground. If, as above, twenty ounces of 

 water, at a medium, perspired in twelve hours' day (i. e.), 

 thirty-four cubic inches of water (a cubic inch of water 

 weighing 254 grains), then the thirty-four cubic inches 

 divided by the surface of all the roots, is = 2286 square 

 inches ; (i. e.) -^- s is = -^ ; this gives the depth of water 



VOL. II. U 



