53 g NEW COMPENSATION PENDULUM. 



The length of The length of the zinc may be varied by means of ihe 



be*alterai!^^ screw EF, and experience alone can determine, whether the 



compensation beaccurate, for, if the clock be foundtog-rtm in 



warm weather, it is evident, that the zinc is too long, and to 



correct it the screw E F, must be advanced; and vice versa. 



Principles of its The quantity of the alteration requisite may be very nearly 



adjusituem. determined by knowing how much the clock has varied from 



its regular rate during a certain period, the difference of 



temperature, and the measure of one revolution of the 



screw E F, which last should be previously ascertained with 



the utmost accuracy. It is scarcely necessary to add, that 



the pendulum must be as much raised by means of the nut 



below g, as it was lowered by shortening the compensation. 



ATstttihet me>de There is another mode of applying a compensation of 



^measa^TOm- ^^"'^ ^^ ^ ''^'^ ^^ v/ood, far more simple than that already de- 



j^easittan to a scribed; but it appears liable to some objections, which ex- 



-w<p*wlea . perience may perhaps prove to be unfounded. The rod is 



made of deal prepared in the manner before mentioned, but 



is suspended from the cock of the time-piece in the common 



way by a spring one inch in length. 



Tfciscompcn- A square tube of zinc, represented at fig. 3, is cast sevea 



jiescriD- j(^(>}^eg long, and three quarters of an inch square; the inter'* 



tial dimensions of the tube are four tenths of an inch each 



side. The lower part of the pendulum rod remains of the 



same thickness^ but is cut away on the two sides for the length 



of seven inches, so as to slide with perfect freedom in the 



tube of zinc. A piece of brass, rather more than a quarter 



of an inch thick, is soldered to the bottom of the tube of 



zinc at C; and a hole with a fine screw is made through it 



similar to that before described in fig. 1. A cylinder of 



zinc of the same description as E F, fig. 1, but only an inch 



and a half in length, is made to screw into the piece of 



brass just mentioned, and a thin plate of brass screws on 



the cylinder to prevent any shake after the length of zinc 



Becessary for the compensation shall have been accurately 



determined. 



In the two opposite sides of the zinc tube two small grooves 

 ^a, h, fig 3) are made with a file at about the eighth of an 

 mch from the top of the tube, and parallel to it, and about 

 the twentieth of an inch in depth. 



A piece 



ed. 



