Registering and Printing Barometer. 



9 



barrel tooth wheel, except when in the act of advancing 

 the tooth. In fig. 2, we have a vertical view of a portion 

 of the mechanism, showing the method of communicating 

 motion to the screw S. The one-tooth wheels, a a', when 

 at rest occupy the positions as shown in the drawing; and 

 being detached from the cog wheel W, it is free to move 

 in either direction. The screw 8, which is shown in fig. 1, 

 is raised or depressed by the revolution of the wheel W. 

 The one-tooth wheels a and a\ moving in the direction of 

 the arrows, give opposite motions to the wheel W; the 

 office of a being to elevate the screw, and of a f to depress 

 it, corresponding to the fall and rise of the mercurial 

 column. 



The mechanism for giving motion to the wheels a and 

 a' is ordinary clock work, each being directly acted on by 

 the barrel wheel, which is driven by a weight. One re- 

 volution of the barrel corresponds to twelve of the wheels 

 a and a'. The axles, to which are attached a, a', carry 

 another wheel having a single half-tooth, as shown in the 

 drawing, fig. 2, which, resting against a little projection on 

 the armature of the magnet, holds the wheel in the 

 position as shown in the figure. 



In order that the wheels a and a f may not revolve with 

 too great rapidity, a train of clock work is connected, con- 

 sisting of two additional axles, a fan being attached to the 

 latter, by means of which the motion can be regulated 

 to any desirable velocity. Three axles would undoubtedly 

 be sufficient, the barrel axle, the axles a, a', and an addi- 

 tional one for the fan. "We adopted the present form, 

 because we happened to have a couple of clock move- 

 ments at hand, and used them just as they were. 



In our first experiments, it was found, when the points 

 p, p f were adjusted very close to the surfaces of the disk 

 d, the oscillations of the barometer were liable to cause 

 both wheels a, a' to revolve at the same time ; and by this 



[Trans, v.] 2 



