45, CORNHILL, E.G., AND 122, REGENT STREET, W., LONDON. 25 



29. Watch Aneroid. Negretti and Zambra have still further reduced 

 the size of the Aneroid to that of an ordinary watch, our engravings, figs. 25, 

 26 showing their exact size. By a beautifully simple contrivance, a milled rim 

 is constructed to move round, and carry with it the index or pointer over the 

 scale engraved on the dial, for the purpose of marking the reading, so that any 

 increase or decrease of pressure may be readily seen. These very small instru- 

 ments are found to act quite as correctly as the largest, and are much more 

 convenient. Besides serving the purpose of a weather-glass in the house or 

 away from home, if carried in the pocket, they are admirably suited to the 

 exigencies of tourists and travellers. They may be had with scale sufficient 

 to measure heights of 20,000 feet ; with a scale of elevation in feet, as well as of 

 pressure in inches, engraved on the dial. The scale of elevation, which is for 

 the temperature of 50, was computed by Professor Airy, late Astronomer 

 Royal, who kindly presented it to Messrs. Negretti and Zambra, for publication.* 

 Moderate- sized Aneroids, fitted in leather sling cases, are found very serviceable 

 to pilots, fishermen, and for use in coasting and small vessels, where a mercurial 

 barometer cannot be employed, because requiring too much space." 



Negretti and Zambra' s Watch-sized Aneroid Barometers, figs. 25 and 26, 

 have now for many years been fully tried and tested, as ordinary Weather 

 Indicators, for obtaining Altitude Measurements, and also for Mining purposes. 

 From the very extensive patronage afforded to them by Government authorities 

 (for Military and Naval service), Engineers, Surveyors, and Scientific Observers, 

 &c., N. and Z. feel justified in giving their unqualified recommendation to 

 these instruments, for Travellers' use, as being both accurate and convenient. 



30. Our woodcuts, figs. 24, 25, 26, show form and actual size of the most 

 useful Aneroid Barometers. Fig. 24 being our Pocket size. Fig. 25 our Watch 

 size, with the simple Barometer Scale of inches and20ths of an inch. This same 

 size instrument is manufactured with Altitude Scales ranging from 10 to 20 

 thousand feet. Fig. 26 is of similar size to the preceding, but has the Altitude 

 Scale arranged to revolve, so that the zero or of this scale being set to the 

 point occupied by the Index at the commencement of the ascent, the elevation 

 attained above the starting point may be at once seen in a rough way on the 

 scale. The divisions of this scale not being absolutely similar all round, causes 

 an error in the reading, therefore, where exact observations are desired, the zero 

 of the scale should be placed opposite to the 31 point, and the indications read 

 off in the usual manner by inches and fractions, their value being known by 

 reference to the Altitude Tables sent with the instrument, so that this form of 

 Aneroid combines both methods of observing in one instrument. 



* See List of Books on Meteorology at end of this seotiou. 



