VOL. LXV.] 



VHlLOSOPHICAIi TRANSACTIONS', 



665 



ence of heat and cold, is also more or less so, as it is more or less rectified. And 

 though the true specific gravity were known at the beginning of the operation, it 

 would even change during the time of using.it, by imbibing moisture from the air. 

 Example. If it were required to know the force of the wind, when the column 

 of water sustained was equal to 4/^- inches. Then, by tab. 1, 



4 inches = 20.833 lb. 



0.5 or i inch = 2.604 



0.1 = 0.521 



sum 4jS = 23.958 = force on every square foot. 



Let w represent the weight 

 of a column of water, having 

 its altitude measured by one of 

 the divisions on the scale, and 

 its base equal to any given sur- 

 face whatever; and let n de- 

 note in general the number of 

 these divisions that measures 



Names of Specific 

 liquors. gravities. 



Water. . 1 .000 



Sat sol. of salt. . 1.244. 



Urine 1 .030 



Ditto 1.016 



Alkohol 0.825 



Proof spirits . . 0.927 

 &c. &c. 



TABLE II. 



Common 

 muUi|ilier. 



J 



Weight Measuring the 

 forces of the wind. 



\ X nw 



1 .244 y. nw 



1.030 X 1IW 



1.016 X nio 



0.825 X rvw 



0.927 X nw 



&c. &n. 



the whole length of the column of the water which the wind sustains. Then 

 nw will represent always its weight, and will serve as a common multiplier for the 

 specific gravities of all other liquors. 



Example. Let iv represent the weight of a column of water ^ of an inch 

 high, standing on a square foot; and let n = 80 = 4 inches. Then, by tab. 1, 

 niv is equal to 20.833 avoirdupois pounds. Therefore 1 .244 X 20.833 = weight 

 of a saturated solution of sea-salt of the same altitude, and ^^ =. the altitude 

 of a column of a saturated solution of the same, weighing 20.833 lb. avoirdu- 

 pois; tv may represent a square yard, the surface of a sail, &c. 



If the velocity and density of the wind in any particular case were accurately 

 determined, this instrument, which gives its force or momentum, would enable 

 us to ascertain the velocity in every other case, the density being known. For 

 it appears from experiments, made by Mr. James Ferguson, p.r.s., on the 

 whirling table, that its force is as the square of its velocity. But as the density, 

 which is one of the data requisite for determining the velocity of this instrument, 

 was not taken into consideration in these experiments, all that we can do at pre- 

 sent is to suggest the idea. 



'''P. s. — ^The wind-gage ought to be somewhat longer than that first mentioned. 

 For they had a gale at Edinburgh May gth, 1775, which supported a column of 

 water of 6^ inches. The force of this gale on a square foot was equal to 

 34.921 lb avoirdupois, and it did great damage to the gardens. West India hur- 

 ricanes would require gages of a still greater length to measure them. 



XXXV. Astronomical Observations made at Leicester. By the Rev. Mr. Ludlam^ 

 Vicar of Norton, near Leicester, p. zQQ. 

 The first observations are a set of zenith distances of stars, to determine the 



VOL. XIII. 



4Q 



