AEROGRAPHER'S MATE 3 & 2 



The mercurial barometer now being issued 

 to naval weather units ashore is the adjustable 

 cistern (Fortin) type, ML-512/GM with mount- 

 ing case ML-48( ). See figure 2-4 for an illus- 

 tration of a Fortin barometer with mounting case. 



Description 



The mercurial barometer, ML-512/GM, con- 

 sists principally of a column of mercury in a 

 glass tube enclosed in a brass casing, a mercury 



FORTIN 

 BAROMETER 



GLASS 

 TUBE 



SCALES 



KNURLED 

 KNOB 



BRASS . 

 CASING 



CISTERN 



209.97 



Figure 2-4.— Fortin barometer with 

 mounting case. 



cistern, and scales for determining the height 

 of the mercury. 



GLASS TUBE AND BRASS CASING.— The glass 

 tube is 34 to 35 inches long, about 0.25 inch in 

 internal diameter, and clear and free from optical 

 defects. The top of the glass tube is sealed, 

 filled with mercury except at its upper end 

 (this end is evacuated), and the open bottom 

 end is immersed in a reservoir of mercury 

 in the cistern. 



The glass tube is supported vertically in the 

 center of a tubular brass casing. The top of 

 this casing is provided with a brass swivel ring 

 by which the instrument is supported in use. 

 This brass casing encloses and protects the 

 glass tube, carries the scales by which the 

 height of the mercury column is determined, 

 provides a track for the movable vernier, and 

 provides a mounting base for the thermometer. 



The glass tube is joined to the cistern by 

 a piece of soft kid leather which is folded in a 

 special manner, tied securely to the constricted 

 portion of the tube, and then tied to the top of 

 the mercury cistern. 



CISTERN.-The mercury cistern (fig. 2-5) con- 

 sists of a small flanged boxwood cylinder (5), 

 a short glass cylinder (8), two curved cylinders 

 (13 and 16) made of boxwood, and a kid leather 

 bag (18). The ivory point (7) projects downward 

 from the roof of the cistern. The mercury 

 cistern is enclosed in a metal cistern housing 

 (19) that is closed by a screwcap (20) at the 

 bottom which carries the adjusting screw (21). 

 Prior to each observation, this adjusting screw 

 is used to raise or lower the level of mercury 

 in the cistern so that the ivory point just per- 

 ceptibly touches the surface of the mercury. 



The leather joint and leather bag are porous 

 to air, but impervious to mercury. This permits 

 the cistern air pressure to be identical with 

 that outside, but prevents mercury leakage. 



In the event mercury is spilled either by 

 leakage or by breakage, it is important to well 

 ventilate the room and clean up the spilled 

 mercury promptly. When mercury is exposed 

 to air or heat it will give off mercury fumes 

 which can be harmful to health. These fumes 

 may even be fatal if breathed in sufficient 

 quantity. 



MOUNTING CASE.— The mounting case, ML- 

 48( ) , is a rectangular box of mahogany or plywood. 

 The cover of this case is split longitudinally 

 through the center, and each side is hinged to 



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