TIMEKEEPERS. <^ 



iddd. These expansion pieces are composed each of two 

 Jaminae, the outside being <>{ brass, the inside of steel. ThRse 

 two pieces are made out of one j the brass being melted upon 

 the steel all in one piece. It is afterward cat into two, de, 

 the steel laminae continued, but made round, and tapped, gg 

 brass balls, or weights, alike in all respects, made to screw 

 npon each tap. In the sides of these balls are two holes 

 between the centre and circumference, made to receive a 

 tool like a two pronged fork, called a fork screwdriver, to 

 screw the balls higher or lower. Jj'two side screws to assist 

 in making the balance of an equal weight, /ik screws to regu- 

 late the mean time, and which are tapped into the shoulders 

 cc, passing through the expansion pieces. The long and .Art ion of this 

 short vibrations being adjusted, I shall next shew how to ^':'i,!''"''' '" 

 make the timekeeper perform alike in heat and cold. The pi.uitiui;s. 

 balance spring becomes weaker by heat, and stronger by- 

 cold, and was the balance to remain of the same diameter, it 

 would go slower in heat, and faster in cold, supposing it to 

 go to time when the thermometer stood ^t temperate. But 

 when the spring becomes weaker by heat, the expansion pieces 

 move toward the centre of the balance, carrying with them 

 the balls gg, by which the diameter of the balance becomes 

 smaller, and relatively lighter. Whfen the balance spring 

 becomes stronger by cold, the expansion pieces move //'o/« 

 the centre of the balance ; carrying with them the balls gg, 

 by which the diameter of the balance becomes larger, and 

 relatively heavier, and when after repeated trials, the balk 

 are properly placed, at equal distances on each tap, the diame- 

 ter of the balance will decrease and increase, in the same 

 ratio as the spring decreases and increases in strength. The Explanatioa. 

 following is the cause of the expansion pieces moving toward 

 the centre by heat, and from the centre by cold. As the 

 outside lamina of the expansion piece is of bras*, and 

 expands, or lengthens more by heat than the inside lamina 

 of steel, to which it is attached ; it will be easy to conceive 

 how the brass forces the steel inwards; and as the same 

 lamina of brass contracts or shortens more by cold than the 

 steel, it is obvious that it must draw it outwards. (Was the 

 lamina of brass placed inside, and the steel outside, the 

 balance would expand, or become larger by heat, and con- 

 K 2 ti,act 



