the Trigonometrical Station on Rumbles Moor, &c. 195 
At Rumbles Moor and at the Observatory the principal angles 
were measured with a twelve-inch repeating circle of a peculiar 
construction, but not calculated to take vertical angles. The 
telescope, two feet in length, and furnished with cylindrical rings 
of equal diameter, and an excellent spirit-level, rests {in a pair 
of Ys) exactly over the upper part of the axis of the instrument, 
and serves to render the line of vision parallel to the plane of 
the divided circle. By fitting the telescope into an axis working 
in the Ys the angles can also be taken in azimuth, but what is 
gained in expedition and exemption from subsequent calculations 
is lost in point of accuracy. Frequent use of the instrument 
produces a shake in the centre, which renders the repeating pro- 
perty nearly worthless. 
At Alfred Castle an eight-inch circle reading off to 15”, and 
fitted up as a transit with a low axis, and a fifteen-inch telescope, 
was made use of. One wire with a mark in the middle was 
found preferable to two. . 
At the other stations, viz. Symon Seat, Beamsley Rock, Carn- 
cliffe, Ilkley Wells, Chevin Beacon, the Bow, Eccles-hill Wind- 
mill, East Ardsley Church, Whitchurch, Jack-hill and Great 
Almias Cliff, the angles were measured by the four-inch theodo- 
lite. The divisions on silver read off tol’. . A plate.and screw 
under the circle enable the observer to repeat the angles either in 
azimuth or in the plane of the three objects. 
A box sextant reading off to 1’, was sometimes used in places 
difficult of access to take the third or verification angle. 
To find the bearings of the different places the theodolite was 
fixed at the station on Rumbles Moor about the time of the 
summer solstice, and very carefully adjusted. The vernier being 
fixed to different degrees on the limb successively, the instants 
of the passage of the first and second limbs of the sun (then in 
the W.N.West) were carefully noted by the watch well regulated. 
The telescope was subsequently pointed at a distant well defined 
station over which the sun had passed during the preceding ob- 
servations, and the angle repeatedly read off. The dednced 
azimuth differed so slightly from the one ‘furnished by calcula- 
tion from data in the Trigonometrical Survey, that either the 
one or the other might be used in computing the latitudes and 
longitudes without materially affecting the result. 
The error of the watch was ascertained as well by sets of ob- 
servations made with a ten-inch reflecting circle and an artificial 
horizon, as by the theodolite itself. 
To find the altitude of any place contained in the anuexed 
list as determined at any particular station where the sector was 
used, add to or subtract from the tabulated heights the feet 
and tenths affixed to their initials. 
Bb2 The 
