336 



Chronometers. 



vanced towards it by less than one fourth part of the quantity, shew- 

 ing that the variation in the rate of going arose chiefly from a dimi- 

 nution of the elastic force of the spring, as seen in the following Ta- 

 ble — 



Having shortened the spring for the fourth experiment, by .01 inch, 

 if the difference of rate had depended on its length, it would have 

 shewn the original rate of +5^.74 at 100°; instead of this, the rate 

 was — 7^0, differing only 3^.3 from the former at the same tempera- 

 ture. To the decrease in length of .01 inch, therefore, is due the 

 loss of 3^3, while to the loss of elasticity is due the difference be- 

 tween 3^.3 and 1 6^.04, the whole difference of rate for 6S°, i. e. 

 + 5^74, at 32° and— 10^30 at 100°. 



The fact having been proved, that glass does not lose its strength 

 by heat in the same ratio as metals, and being now acquainted with 

 the extent of its loss, which was 40^ for 68° of Fahr. we next had 

 to construct a balance suitable to correct so small an error, and our 

 previous experiments having pointed out to us that a metallic bal- 

 ance was unfit for such a purpose, we continued to employ the glass 

 disk 6, as shewn in the annexed diagram — 



to which was attached the glass balance-spring a. To the disk we 

 applied in an horizontal position, two laminas composed of platina, 



