18 



KEGRETTI AND ZAMJ'.KA, HOLBORN VIADUCT, E.G., 



It will be seen that owing to the great length of the tube, viz., 27 feet, 

 Jordan's Barometer can only be fitted up in very few buildings. To gain the 

 advantage of so extended a range of scale in a convenient sized instrument, 

 Messrs. Negretti and Zambra have constructed their 



NEW LONG RANGE MERCURIAL AND GLYCERINE 

 BAROMETER, 



.28 



B 



-31 



24*. The Long Range or Open Scale Barometer 

 is shown in section in fig. 19. It consists of a 

 glass tube of the syphon form ; one side of the 

 syphon, A, or closed end, being about 33| 

 inches long, and the other only a few inches in 

 length. To this short end is joined a length of 

 glass tubing, B, of a much smaller (internal) 

 diameter ; both tubes are of equal length, the 

 smaller one being open at the top. The large ||_2|| 

 tube, A, is filled with Mercury, and the small 

 tube, B, partly filled with Glycerine, a fluid 

 many times lighter in specific gravity than 

 Mercury ; the rising and falling of the mer- 

 curial column in the large tube having a lighter 

 fluid to balance, and that dispersed over a 

 larger space by reason of the difference in the 

 diameter of the two tubes, a longer range is 

 obtained, due loth to the unequal capacity of the 

 tivo tubes and the difference in the specific gravity 

 of Mercury and Glycerine. 



The range of these barometers is from six to 

 ten inches to the inch of the ordinary Mercurial 

 Barometer, yi^ of an inch can easily be 

 observed without the use of a vernier. It is a 

 most interesting instrument, as from the extremely extended 

 scale the slightest variation is plainly visible. The actual 

 size and form is about that of an ordinary Barometer, as 

 seen in fig. 20 ; extreme length about 40 inches. 



FAIR 



FIG. 20. 



FIG. 19. 



Price, as fig. 20 ... 

 Do., with Portable Stop Cock 



5 5 

 5 10 



