20 



NEGEETTI AND ZAMBEA, HOLBOBN VIADUCT, E.G., 



contact with it. The framing, which carries the scale and marker, is an 

 arrangement of brass bars, delicately adjusted and controlled by springs, so 

 as to permit of a quick horizontal motion being communicated to it by the 

 action of the hammer, E, of the clock, whereby the point of the marker is 

 caused to impress a dot upon the paper. The same clock gives rotation to the 

 cylinder, D, upon which is mounted the registering paper. The clock must be 

 re- wound when a fresh paper is attached to the cylinder, which may be daily, 

 weekly, or monthly, according to construction ; and the series of dots impressed 

 upon the paper shows the height of the barometric column every hour by day 

 and night. The space traversed by the marker is precisely equal to the range 

 of the barometric column. 



Price, in an Ornamental Oak Case, fig. 21 18 18 and 22 



26. King's Self - Registering 

 Barometer. Mr. Alfred King, Engineer 

 of the Liverpool Gas-Light Company, 

 designed, in 1854, a barometer to register, 

 by a continuous pencil- tracing, the varia- 

 tions in the weight of the atmosphere ; 

 and a highly-satisfactory instrument, on 

 his principle, and constructed under his 

 immediate superintendence, was erected 

 at the Liverpool Observatory. 



Fig. 22 is a front elevation of this 

 Barometer. A, the barometer tube, is 

 three inches internal diameter, and it 

 floats freely (not being fixed as usual) in 

 the fixed cistern, B, guided by friction- 

 wheels, W. The top end of the tube is 

 fastened to a chain, which passes over a 

 grooved wheel, turning on friction rollers. 

 The other end of the chain supports the 

 frame, D, which carries the tracing 

 pencil. The frame is suitably weighted 

 and guided, and faces the cylinder, C, 

 around which the tracing paper is 

 wrapped, and which rotates, once in 

 twenty-four hours by a clock movement. 

 For one inch change in the mercurial 

 column the pencil is moved through five 

 inches, so that the horizontal lines on the 



FIG. 22. 



