93 



The apparatus employed consisted of a small glass retort only, the 

 globular receiver being surrounded by a certain quantity of water of 

 known temperature. Two hundred grains of the liquid, whose vapour 

 was to be examined, were rapidly distilled from this retort into the 

 globe, and the rise of temperature in the surrounding water became 

 the measure of the latent heat. A table follows, exhibiting the experi- 

 mental results on the latent heat of several vapours : whence it ap- 

 pears that 967 is the latent heat of steam, 442 that of alcohol ; of 

 ether, 302'3; of oil of turpentine and of petroleum, 1 77' 8 ; of nitric 

 acid, 531-9; of liquid ammonia, 837'2; and of vinegar, 875. 



The paper concludes with a proposal for employing the vapour of 

 alcohol in certain cases, for the purpose of propelling machinery'. 



Observations on the Heights of Mountains in the North of England. 

 By Thomas Greatorex, Esq. F.L.S. In a Letter to Thomas Young, 

 M.D. For. Sec. R.S. Read May 7, 1818. [Phil. Trans. 1818, 

 p. 395.] 



Wishing to measure Skiddaw geometrically, the author employed 

 a staff about 28 feet long. Its graduation commenced at 0, placed 

 about 3 feet above its lower end, from which to the top was ex- 

 actly 25 feet. A stationary barometer was next placed 10 yards 

 above the lake, and its variation and that of a thermometer were 

 noted every half hour. Another barometer and thermometer were 

 then set upon the summit of the mountain, and their respective heights 

 accurately observed. A telescope, with cross wires, was then care- 

 fully levelled, and the wires made to intersect the highest point of 

 the mountain. It wa& then pointed in the direction of the most con- 

 venient descent, and the staff carried down the hill till its top exactly 

 coincided with the cross wires, the level of the telescope being care- 

 fully preserved. The perpendicularity of the staff was ascertained 

 by plumb lines ; and as it was seldom more than 40 feet from the 

 telescope, no allowance was necessary for the earth's curvature. The 

 most exact mode of managing the pole, says the author, was to stop 

 my assistant when I observed its top to be about an inch above the 

 cross wires, and then it was pressed gradually into the earth till an 

 exact coincidence was obtained. The telescope was then carried down 

 to the pole, levelled and placed in exact correspondence with zero. 

 The pole was again carried to a new station, and this mode continued 

 for fifty yards of descent. The barometer was then again set up and 

 examined, and the process continued to the foot of the mountain. 

 The height of Skiddaw, by levelling, was 1012 yards 3^ inches. 



Annexed to this paper are the results of several barometrical ob- 

 servations made on the summit of Skiddaw, and continued at different 

 distances of fifty yards each down to the foot of the mountain. 



