192 “Account of the Levelling taken from 
curvaturé, being opposed to each other in quantities nearly equal, 
need not enter into the calculation. 
In a second attempt to find the fall, the distances when even 
slopes presented themselves were sometimes as much as 2000 
feet, and little attention was paid to the placing of the theodo- 
lite precisely at the medium distance. : 
The route adopted is upwards of four miles ; yet the aggregate 
fall to various places, as determined by the two methods, rarely 
differed more than a foot. The mean gave 976 feet for the 
total perpendicular descent. 
Finally, A third or verification levelling was effected in nearly 
a direct line to the canal. The distances were repeatedly mea- 
sured with tapes of different lengths, and the angles were taken 
with the horizon-sector. ‘The last distance was found trigono- 
metrically from two bases, all the three angles being observed. 
The sector was moreover taken to both stations, and the zenith 
distances reciprocally observed. The result is one foot less than 
the mean of the preceding essays. 
420:5 ft. 0 57 20 clev. 7:01 fall 
646-0 3 11 50 dep. 36°00 
1362°5 2 34 50 elev. 61-34 
1361°8 3 18 15 dep. 78°49 
1576°4 4 48 32 elev. 1382°15 
1577°6 = 3:17 «47 dep. 90°83 
7841-0 4°6 4 dep. 562-00 
Height of instrum. oe 7'20 
Fall to canal at E. Morton 975°02 
Do. to basin at Liverpool 289-00 
Do. to low-water mark 54:00 
Height of Rumbles Moor \ 1318 
above the Irish sea 
The last distance is horizontal; the others hypothenusal. 
The altitude of the observatory was ascertained by a different 
and perhaps more satisfactory method. The elevations of three 
well defined (but inaccessible) objects, situated between the ob- 
servatory and the canal, were carefully determined at a station 
on the banks of the latter. The depressions observed at the 
first-mentioned place gave the corresponding fall, and their sum 
the elevation of the observatory above the canal*. .The distances 
were found trigonometrically, from stations linked to the Ord- 
nance survey, and were of course of accurate origin. 
* When the intermediate object is equi-distant from the two stations, the 
refraction may be disregarded. . 
In 
4 
} 
x 
