1830.] 
On determining the Height, e^c. 
353 
have caused much injury to the canal banks. The horse was very much exhausted 
when he got to Paisley, though by no means so exhausted as he was about the 
middle of the journey, having sensibly recovered after the first four or five miles. 
Two post horses were hired there ; and lighter towing lines being attached to the 
boat, it started again, on its return to Glasgow, with twenty-four persons on board, 
four of whom were boys, and arrived at Glasgow, a distance of 7 miles, in forty- 
five minutes. The greatest speed attained during the journey was two miles in 
eleven minutes. During this voyage the surge behind was entirely got quit of, 
even at the curves, where it was reduced to nothing ; and thefe was no front wave, 
except at the bridges. It appeared only at the bridges, and just as the boat was 
about to enter under the bridge, and gradually disappeared as the stern of the 
boat cleared the bridge. The quicker the boat went, the more entire was the dis- 
appearance of all wave and surge, except where the water escaped in the centre of 
the canal, and met in two very noisy and rapid currents from each side of the boat 
at the rudder. This noise and rush of water was so great behind, as to induce per- 
sons on board to look round, expecting to see a great wave or surge on the bank of 
the canal, but on the banks there was hardly a ripple. The two rapid noisy currents 
seemed to be completely spent and exhausted by the shock of their concourse be- 
hind the boat. Here, therefore, there was no room to doubt ot the correctness of 
the reports of the Forth and Clyde Canal experiments. It was not merely to be 
said that the greater the speed the less the surge or wave, but it was demonstrated 
that, at a high rate of speed, surge and wave were done away with altogether. Un- 
luckily, there was no Dynamometer attached to the rope, so as to ascertain whe- 
ther, contrary to all theory, the strain or pull was not equally diminished with the 
wave, and the tugging labour of the two horses lessened instead of increased, by 
the accelerated rate at which they drew the boat. There can be no doubt, however, 
that with one trained horse, properly attached, the distance could be done in a 
period under 40 minutes. Contrary to expectation, Mr. Wood’s boat was quite 
steady in the water, and by no means crank. It may be proper to mention that 
the Ardrossan Canal is throughout very narrow ; at the bridges and many other 
places it is only nine feet broad. It has a great number of turns, and many of 
them very sudden. 
Vlf .—On determining the Height of a place from Observations of the 
Depression of the Horizon. By Lieut. R. Shortreed, Bom. Est. 
There are various well known methods of finding the height of a place above the 
leve> of the sea. The following method has not yet been generally put in prac- 
tice ^ but from several trials I am disposed to consider it capable of considera- 
ble correctness. Having a number of stations within sight of the sea, it occurred 
to me that their elevation might be found very simply, and independent of other 
observers, by measuring the depression of the sea. 
I resolved, therefore, to try it along with the other methods by barometer, and 
by a series of elevations and depressions, from station to station, and for this 
purpose calculated the following table. , , . , . , 
Let be the radius of the earth = r, and in order to connect the heights h, with 
the angle of depression = d , we have cos. d= whence r cos. d + h cos. d= r 
T (1 — COS. d) 
and h cos. d= r — r cos. d—r (1 — cos. d ) and dividing, h = • 
2 sin. * £ d 2 sin. i d sin. i d sin. d sin. $ d 
cos. d 
= r tan d tan £ d by 
cos. d cos & cos ' ^ ^ C0S ’ ^ 
which formula the table is calculated. I have = 20921850 feet i 
in the 1st Vol. of the Trig. Survey of England and W ales the logarithm of which 
— 7 q* 7 060 00 When the depression does not exceed 10 or la with a tolera- 
hie instrument, this is probably one of the easiest and most correct modes of 
finding the height of a place. When the depression exceeds 1 degree, the proha.- 
bility of error is much encreased by the uncertainty of retracUon-which, however. 
