194 Account of the Levelling taken from 
In caleulating the heights of the stations the refraction was 
determined by the reciprocal observations, but in computing the 
altitudes of the other places in the list the zenith distances were 
INVARIABLY increased |-15th of the arc, minus 25”, the error 
of the instrument. 
When an object was observed only during the existence of the 
diurnal refraction, and the extremes were not marked, the only © 
resource consisted in comparing it with a nearly contemporary 
observation of another object, of which the constant angle had 
been subsequently noted. The correction is nevertheless some- 
what arbitrary:; for the variation does not affect the whole of the 
observations either at the same time, or in the same degree. 
To ensure greater accuracy to the altitudes of the statzons, the 
following method was resorted to. 
Rumbles Moor, as has been already demonstrated, is about 
1315 feet high, and the altitude of any other object in its vicinity 
might be obtained by using the sector at a third station equi- 
distant from the other two, without making any correction for 
refraction, or trival constant error of the instrument. When 
the distances are not precisely equal, allowance, it is true, must 
be made for refraction, &c. but great precision as to their value 
is net absolutely requisite to produce a correct result. It would 
however be possible to quote a solitary yet very marked excep- 
tion, occasioned no doubt by an extraordinary state of the at- 
mosphere i in the direction of the object. 
A few of the observations made on Pendle Beacon are ad- 
duced by way of ilfustration. (It is unnecessary to reduce the 
angles to the ground.) 
Sep. 24, 1822. Left Index. Rt.Ind. Therm. Dist. in Are. 
he my i" feet. Feet. 
10 50 AT Rum. Moor dep.24 53 25 10 48 2 102506 East 16 46 517°8 lower. 
13° (0 Do. 24 53 Une (ASH 
11 20... Ingleboro. elev. 812 $12 492 110820 N. 1813 529-7 
13 45 .. Pennigent elev. 6 40 643 49 105492N.N.E.17 18 446-0 
N.B. The sector reversed accurately at 60°. The refraction 
used is 1-15th—25”. 
With these data and 1318 feet the altitude of Rumbles Moor 
we have 2310-6 for the elevation of Great Whernside, 2365°6 
for that of Ingleborongh; and 2281-8 for that of Pennigent, 
In determining the distances in the survey the bases used were 
Rumbles Moor to Boulsworth Hill 68370 S.W. 
Ditto ¢ Pendle Hill 102506 W. 
Dive. °". § Gt. Whernside 101114 N.N.W. 
Ditto “sr Wakefield Spire 107386 S.E. 
' See Trig. Survey, 3d volume. 
higher. 
11 45 .. Gt.Wherns. elev. 353 355 483 124750 N.E. 20 27 re 
At 
