Chronometers. 337 
¢,c. ‘These pieces were in length 0.5 in., breadth 0.052 in., thick- 
ness 0.004 in. and weight 2 grains. The lightness and thinness of 
these pieces only allowed of one method of compensating for tem- 
perature, which was to cut off with a pair of scissors a small portion 
from the top, and to draw out the timing screws d, d, to bring the 
chronometer to mean time again, in consequence of the balance hav- 
ing been lightened by cutting off a piece from the compensation Ja- 
mine 
The compensation being completed, we next proceeded to test. 
the isochronism of the glass spring ; in which respect it was proved 
to be as perfect as any metallic spring. The whole of the adjust- 
ments being now completed, we finally tried its rate under different 
degrees of heat, from 12° to 100° Fakr., and are of opinion, that 
there was less error shewn than generally attends metal springs, un- 
der corresponding circumstances. The chronometer with this glass 
spring and balance, was sent to the Royal Observatory, agreeably to 
the order obtained from the lords commissioners of the Admiralty, in 
October, 1833. 
There have been two causes why the investigation has been de- 
layed; first, until the last winter, the thermometer did not fall suffi- 
ciently low to enable us to draw a fair conclusion; secondly, there 
has been an acceleration, on a gaining rate, since it has been placed 
on trial ; and this has been the sole obstacle to the complete success. 
of this experiment. This acceleration must, therefore, be a subject 
of further research: that it arises from some latent cause, would ap- 
pear from the circumstance, that the two chronometers, placed on trial 
by order of their lordships, as well as others which we have had in 
our possession for private experiment, have gained nearly in the same 
ratio. Of the two chronometers tried by order of their lordships, 
No. 616 has been stationary at the Royal Observatory, and No. 790 
on board H. M. S. Fairy, Capt. Hewett, employed in surveying in the 
North sea. On the close of the season, this latter chronometer was 
returned to the Royal Observatory, until required ; therefore, (with 
regard to this chronometer,) we have both a sea and land rate. The 
annexed tables shew the going of the two chronometers. From 
these tables it appears that the chronometers gained most at the ear- _ 
liest period of their trials, and our object is to watch the termination 
of their acceleration. 
If we might venture to offer some practical remarks on the nature 
of balance springs which have been subjected to the effects of fire 
Vou. XXXII.—No. 2. 43 
