179 
Mr Dickson on a new Water-Pressure Engine. 
100 gallons per minute is equal to a certain power with 1 foot 
of fall, 1 gallon per minute will perform the same work with 
a fall of 100 feet. Its local conveniences also are considerable ; 
for besides retaining the power of‘ the fall below at any distance 
short of 34 feet perpendicular, that fall, with the fall to the en- 
gine, may be at any slope : There is no dampness where it 
works, — ^it requires no attendance, — is not so liable to go out of 
repair as a steam-engine, — it is less expensive,— and, if the 
power is the same, occupies still less space. 
One of these engines has been erected for Sir Alexander Jar- 
dine, Bart., of Applegarth, for the purpose of driving his. 
thrashing-machine. There is from 8 to 12 feet of fall, (accord- 
ing to the height of water in the reservoir) to the cylinder, and 
30 feet of fall from it ; and to gain this perpendicular height, it 
required 136 yards of pipe. Of this pipe, 80 yards is 6 J inches 
diameter, and 56 yards 5J. The valves are 4 inches and the 
cylinder 12 inches diameter, with a stroke of 2 feet, and 8 double 
strokes in the minute. The drum, which is 30 inches in dia- 
meter, performs 272 revolutions in a minute. The engine con- 
sumes nearly one cubic yard of water in the same time, and 
works with the power of two horses^. 
29. Gilmour Place, ) 
2m May 1820, | 
Art. XXX. — On the Retrograde Variation qfthe Needle. By 
Colonel Beaufoy, F. B. S. &c. &c. In a Letter to Dr 
Brewster. 
Bushey Heath, Stanmore, 
Dear Sir, 1st May 1820. 
In addition to the mean^monthly variation of the magnetic 
needle, I have the pleasure to send you a general Table, con- 
taining my observations for three successive years, from whence 
it appears, that the maximum of the western variation at this 
place occurred about the month of March 1819; that such is 
the fact, is evident, because in the first nine months of the se- 
cond year’s observations, the variation was greater than during 
• We hkve seen letters, from which it appears, that Sir Alexander Jardine, 
a competent judge of machinery, is highly satisfied with the performance of this 
engine. — ^E d.' 
M % 
