tmafuring Heights with the Barometer. 721 
between the refults, they found the mean defcent to be 
117.38 feet : hence Arthur’s Seat is above Leith pier, by 
the mode of levelling, 802.66 ; and by the mixed me- 
thod 803 feet. 
In 1774, when the aftronomer-royal was carrying on 
the Society’s experiments for afccrtaining the attraction 
of Schihallien, I found, from my own geometrical opera- 
tions, depending on a bafe meafured in the plain near 
Tay bridge, the Weltern fummit of the mountain to be 
1 1 83 feet above the South obfervatory. 
Of this height, the effeCt of curvature and refraCtion 
amounted to 28.86 feet, on the diftance of Bolfracks 
Cairn from the obfervatory; and to 38 feet, on the dif- 
tance of the faid Cairn from the fummit of Schihallien. 
The refult of thefe operations I communicated to Mr. 
maskelyne, before his trigonometrical operations were 
begun. From the data which he hath fince been fo 
obliging as to furnifh me with, depending on the bale m 
Glen more at the bottom of Schihallien, and the angles 
of elevation taken from the Southern extremity of that 
bafe, the Weftern fummit of the mountain is t 186.6 
feet above the South obfervatory. But if the triangle 
that ferved to connect the itation of the barometer in 
that valley with the others, and the angles of elevation 
taken from the lame Itation are made ufe of, the aif- 
4 Z 2 
:erence 
