t 
234 New Form of Mountain or other Barometer. 
In planning my barometer, besides the abstract principles which 
must of course govern in any ascertainment of the weight of the 
atmosphere directly by experiment, I had these two concrete 
ones for guides :— 
Ist. That the mercurial column should be throughout so expos- 
ed to view, that no fracture, irregularity, in-crept air or other acci- 
dental affection of its trustworthiness, can escape instant notice. 
2nd. That the observer be left at all times free, to employ only 
so much of the auxiliary apparatus as fits the object he may have 
in view, or the refinement (not the certainty) he may aspire to. 
Hence nearly every one of the few pieces that compose the read- 
ing of the result is entirely detached, and to be added or removed 
at pleasure: in the case of its employment as a stationary barom- 
eter, this may be said of every piece. 
The extent, to which these principles and others accessory to 
them have been carried out, is seen in fig. 1 of Plate [V, accom- 
panying this description. The entire instrument is here shown, 
with all its parts in suitable positions for use. These parts are, 
1. A small rectangular steel bracket, with a gimlet-pointed 
screw for clamping it to any convenient upright wooden support 
by one arm; while the other is pierced to allow the passage of 
the stem of the suspension hook. is 
2. The suspension hook, made of a single piece of steel; suit- 
ably bent at one end, the bearing-part of which is also fashion 
into a knife-edge ; the other end being screw-cut and receiving, 
after its being passed through the bracket, a nut by which its ver- 
tical motion is produced and its position regulated. A washer in- 
tervenes between this nut and the bracket: but otherwise there 
is no provision for any azimuthal motion, such a motion, more 
than the nut itself has, being unnecessary. In elevating or depres- 
sing the tube, it is only required to prevent the hooked end from 
turning horizontally; by the finger, the revolutions of the nut 
then have all their proper effect. 
3. The corve, or basket-handle, for carrying the tube. The 
rim and arms of this are cut out of a piece of clock-spring; the 
cross-bar of steel is.a knife-edge corresponding with the bearing 
part of the hook; the excess in length of the rim over the cireum- 
ference of the tube is bent from both ends equally to allow of 
forming clamp-jaws; one end is reinforced in thickness with @ 
piece of steel riveted to it, in which a screw thread is cut; and 
