364 SURVEY OF THE COAST 



The dial plate is thickly plated with silver, in order to pre- 

 serve well tiie whiteness, which facilitates the reading, while 

 the mere silvering commonly used, soon becomes so dull as 

 to render tlie reading by night or from a distance inconve- 

 nient. 



With the same views — to facilitate the reading, the circle 

 of the second hand is larger than usual, and all useless num- 

 bers are excluded, in order to give to the divisions a more 

 striking appearance. 



It was my intention to make the weight always move at 

 some distance even, below the lens of the pendulum, to avoid 

 the too great influence of it upon the j)endulum, particularly 

 in the proximity of the lens, as it is a well known fact, that 

 the clock will always change its rate of going in consequence 

 of the mutual attraction between the lens and the weight. 



In clocks which go only twenty-four hours, as those de- 

 scribed above, which are always wound up at regular times, 

 this influence, occurring every day equally, will on the whole 

 compensate itself, and the intermediate deviations occasion- 

 ed by it will remain concealed, as the clock will always be 

 regulated according to its mean daily rate. It appears there- 

 fore the most evident in those clocks which go a long time 

 with one winding. On a Franklin clock, which I put up at 

 West Point in 1808, and which shows only four hours, and 

 went forty days with one winding, the pendulum was com- 

 pletely stopped when the centre of gravity of the weight was 

 about ten inches below that of the lens, their horizontal dis- 

 tance being three inches and a quarter ; the weight and lens 

 both were considerably heavy. 



To counteract this mutual influence, I hung a musket ball 

 by a thin wire from the board on which the clock rested to 

 the point where the centre of gravity of the weight was 

 when the clock stopped, and in a few seconds it began to os- 

 cillate isochronous with the pendulum. 



These two experimems I repeated several times, with ex- 

 actly equal results ; and though 1 attributed the stopping of 

 the clock to a small defect in its position, I made the weight 



