32 Sketch of a New Indestructible Portable Mountain Barometer. [Japt, 



access to the atmosphere to exert its pressure on the mercurial column. 

 It is evident that any fluctuations in the height of the columns of mer- 

 cury will be immediately communicated tc the indicator, either by the 

 float being pushed up if the mercury rise in the short tube, or by its 

 sinking down when it falls. The scale, it is unnecessary to observe, 

 must be graduated downwards, and a properly marked vernier attached. 

 To protect the indicator, scale and attached thermometer, &c. a thin 

 cylinder of brass is fitted round the barometer, as explained in the 

 sketch. Two vertical openings are cut in this, which when the brass 

 cylinder is properly adjusted render the scale and thermometer visible j 

 fhe indicating wire is thus preserved from wind and accident. The 

 stctle here marked allows for a range of ten inches, which is considered 

 sufficient, being equivalent to a difference of level of more than 11,600 

 feet. For particular purposes, however, this may be easily extended. 

 When packed for travelling, the float and its indicator can be nicely 

 fitted into the brass cover before mentioned, and more than one of these 

 should be kept for use. The diameter of the bore being half an inch, 

 with a cistern at top of one-inch diameter, and three inches long, about 

 five lbs. of mercury will be required to fill it, the weight of the iron 

 tube, and other apparatus connected with this barometer, may probably 

 be about 4a lbs. more ; thus the total weight will be under 10 lbs. 



EXPLANATION OF THE FIGURES. 



Fig. I. — Self-Registering Apparatus. —A— is the screw for adjusting the height of the 

 instrument relative to the clock work ; by this it can be raised or lowered at pleasure. — 

 B — a leveller nicely balanced on a knife-edge centre, with a circular ring at one end, to 

 embrace the indicator of the float ; at the other end is an ever pointed pencil on Mor- 

 dan's principle, with a small spiral spring within, which keeps it continually pressed 

 against the revolving barrel. — C— The revolving barrel which may carry covers of paper, 

 ass' skin, ivory, &c. The vertical lines represent the hours and minutes ; the horizon- 

 tal lines are inches divided into the usual number of parts. A fresh cover is fixed on 

 every 24 hours, by stopping the machinery and adjusting it to any particular moment, 

 on attaining which by a watch the machinery is started. 



Great wheel 120 — Second wheel 120, pinion 10 — Pallet wheel 90, pinion 6 — Motion 

 wheels 30 and 60 — Circumference of barrel 24 inches — one revolution in 24 hours. 



Fig. 2.— Front view, shewing the brass cover intended to screen the indicating wire 

 from the wind. This cover is moveable round the barometer, and the opening here dis- 

 closes the scale, which can be easily read off. When travelling this brass cover is moved 

 round so as to protect entirely the scale Thermometer and the wafer with its indicator. 



Fig. 3.— Side view— The opening here in the brass cover (adjusted as above to disclose 

 the scale) exposes the Thermometer attached to the Barometer. 



Fig. 4.— Tube of thin iron about l-8th of an inch thick, total length out and out 34 1-Rth 

 inches; the shaded part represents the column of mercury. 



c - 



