26 REPORT—1863. 
that this fact may be expressed by saying that the whole disturbing force acts in 
one plane, which is evident, inasmuch as the two components alluded to are in 
one line. The comparison of these curves is believed to confirm results which have 
been obtained, without the aid of photography, chiefly through the sagacity of 
General Sabine; for it appears that at Lisbon the vertical force and east and west 
force are affected by only one type of disturbance, while the north and south 
force is under the influence of two different types; and it is believed that at Kew 
both types operate upon each of the three elements. 
On a Mercurial Air-Pump. By J. W, Swan. 
In general arrangement and appearance this instrument resembles a barometer, 
with a reservoir at the top and a reservoir at the bottom of the tube. Both reser- 
yoirs are of considerable capacity, but the lower one is the largest. The lower 
reservoir has two pipes entering it, namely, an inlet and outlet, and each has a 
stopcock. The upper reservoir, termed a vacuum-chamber, is surmounted by a 
ball-valve opening outward, and has also a tube with a stopcock communicating 
with the vessel to be exhausted. The vacuum-chamber, tube, and a portion of the 
lower reseryoir are, in the normal condition of the apparatus, occupied by mercury, 
The remaining space within the lower reservoir is filled with water, which is 
separated from the mercury by a caoutchouc bag, tied on the lower end of the 
tube containing the mercurial column. The inlet pipe entering the lower reser- 
voir is connected with town water-pipes or a force-pump. The working of the 
pump is effected by opening the outlet pipe so as to permit the mercury to vacate 
the vacuum-chamber and ascarid to the barometric level, displacing the water 
from the lower reservoir. Then the vacuum formed having been taken advantage 
of by opening the communication between the vacuum-chamber and the vessel to 
be exhausted, the original condition of things is restored by closing the outlet pipe 
of the lower reservoir, and opening the inlet, so as to supply water at a high pres- 
sure, which will force the mercury to reoccupy the vacuum-chamber, the valve at 
the top allowing the exit of its more or less attenuated gaseous contents. This 
process, being frequently repeated, will, no doubt, give a very perfect vacuum, as 
there is no obstruction, of the nature of a valve, between the vacuum-chamber and 
the vessel to be exhausted. This air-pump was said to be specially adapted for the 
exhaustion of small vessels. It was proposed that the instrument should be made 
entirely of wrought iron ; among its advantages were small cost and simplicity, its 
efficiency not depending upon fine aotenuanclty, 
Description of the Experimental Series of Rain-Giauges erected at Calne. 
By G, J. Symons. 
These instruments have been constructed and erected at the expense and in the 
grounds of Major Ward, of Castle House, Calne, with a view of finally deter- 
mining the size and form of gauge which most truly indicates the amount of rain 
actually reaching the surface of the earth, and also deciding both the best elevation 
at which to place the gauge above the ground, and, if possible, the correction 
requisite to reduce the observations made at other elevations to what they would 
have been if made at the adopted standard height, The series consists of two sets 
of gauges: those for testing the indications of different-sized gauges are eleven in 
number, consisting of circular ones, 1in,, 2in., 4in., 5in., 5in. with a peculiar 
flange or lip, 6in., 8 in., 12 in,, and 24 in. in diameter, and square ones of 265 in. 
and 100 in. in area. These are all placed at the same height above the ground 
(1 foot), and are very near to each other. The elevation series consists of nine 
gauges of 8 in. diameter, placed at the following heights above the ground, viz., 
level, 2in., 6in., 1 ft., 2ft., 3ft., 5ft., 1Oft., and 20ft.; and at some distance from 
each other. A second gauge of 5 in. diameter is placed 20ft. above the ground, in 
order to ascertain if its indications at that height bear the same ratio to an 8-inch 
gauge as at a less elevation. The instruments being erected in a very favourable 
position, free from the influence of trees or buildings, and elevated on poles, it is 
anticipated that the results will be more reliable and available for the before-men- 
tioned purpose than if placed upon buildings. 
