946 APPENDIX. 



2796d. Negretti and Zambra's Self-registering 

 Mercurial Barometer. Negretti and Zambra. 



In this instrument the various parts of the mechanism have been so arranged 

 that the recording is effected by means of a clock, which causes a drum to 

 revolve, carrying round it a paper. On this paper is traced the barometric 

 curve by a pencil attached to a float, and placed on the mercury of a syphon 

 barometer tube. 



See Negretti and Zambra's Treatise on Meteorological Instruments. 



2796e. Howson's Patent Long Range Barometer. 



Negretti and Zambra. 



In this barometer the tube is fixed, but its cistern is sustained by the upward 

 pressure of the atmosphere. Looking at the instrument it appears as though 

 the cistern with mercury in it must fall to the ground. The bore of the tube 

 is about an inch across. A long glass rod is fixed to the bottom of the cistern. 

 The tube being filled with mercury, the glass rod is plunged into the tube as 

 it is held upside down, and when it is inverted the mercury partly falls and 

 forms an ordinary barometric column. The cistern and glass rod, instead of 

 falling away, remains suspended. There is no material support to the cistern ; 

 the tube only is fixed, the cistern hangs to it. The glass rod, being so much 

 lighter than mercury, floats and sustains the additional weight of the cistern 

 by its buoyancy, and the almosphere acting on the mercury keeps up the 

 barometric column. 



2796f. Long Range Barometer. Negretti and Zambra. 



This instrument consists of a mercurial tube on the syphon principle, one 

 side of the syphon, the closed end, being about 33 inches long, and the 

 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 tile 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^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. 



28O9e. Metal Barometer. 



Dr. Wilhelm Tinter, Professor of Practical Geometry at 

 the I. R. Polytechnic Institute at Vienna. 



2816a. Pocket and Watch-sized Aneroid Barometers. 



Negretti and Zambra. 



The patent for the aneroid having expired, the late Admiral Fitzroy urged 

 upon Negretti and Zambra the desirability of reducing its size as well as 

 improving its mechanical arrangement, and compensating it for temperature. 

 They after great labour and numerous experiments, succeeded in reducing the 

 dimensions to less than three inches in diameter and two inches in thickness. 

 These instruments have since been further reduced by Negretti and Zambra, 

 until they have at last reached the dimensions of an ordinary watch. These 



