II. BAROMETERS. 679 



other only a few inches in length. To this short end or leg is joined a length 

 of glass tubing of a much smaller (internal) diameter, both legs being of 

 equal length ; the smaller tube is filled with a fluid many times lighter in 

 specific gravity than mercury, the rising and falling of the mercurial 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 both to the unequal capacity of the two tubes 

 and the difference in the specific gravity of the mercury and the second fluid 

 employed. The range of these barometers is from 6 to 10 inches to the inch 

 of the ordinary mercurial barometer; the y^j-th 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. 



Large Household Barometer, for ordinary use. 



Negretti and Zambra. 



Domestic Standard Barometer, of the same construction 

 as 27963, but of smaller size. Negretti and Zambra. 



2797. Mercurial Barometer, an old Dutch instrument by 

 Reballio, combining syphon and long range barometer, thermo- 

 meter, and hygrometer. Pillischer. 



2798. Drawing of a " Balance " Barometer, of which a 

 model was executed, submitted to the Royal Irish Academy, and 

 tested during some months. Jos, P. O'Reilly. 



The column is inclined from the vertical, and suspended by a knife edge, as 

 the beam of a balance, whence the proposed name. The displacement of the 

 mercury in the column causes this to incline more or less from the vertical, 

 the amplitude of movement showing itself on a graduated limb by means of 

 an index. The mode of action and the degree of sensitiveness of the instru- 

 ment are therefore comparable to those of a beam balance, and the indications 

 given without the intervention of wheel work. 



2799. Barometer of De Luc, formerly belonging to H. B. 

 de Saussure, and carried with him in his Alpine excursions. 



H. de Saussure, Geneva. 



2800. Meteorological Barometer by Wild, used in all 

 meteorological stations throughout Russia. 



Geneva Association for the Construction of Scientific In- 

 struments. 



This barometer is a combination of Fortin's barometer, and Gay-Lussac's 

 old siphon barometer. For minute description, see " Melanges physiques et 

 chimiques, tires du Bulletin de 1'Academie Imperials des Sciences de St. 

 Petersbourg," vol. ix, 23rd September to 5th October 1875. 



2800a. Barometer of a New System of Construction. 



W. Gloukhqff, Ministry of Finance, St. Petersburg. 



For taking an observation with this barometer, the mercury of the cistern is 

 forced to pass by means of the screw A through the hole a into the open 

 space m n, formed by a glass ring, and to cover its bottom. Then the movable 



