33^ ' Chronometers. 



The obstacle which seemed to present itself to the use of glass in 

 the chronometer was its extreme fragility ; this however, proved to 

 be no obstacle, and having prepared a glass balance spring, we took 

 a previously adjusted chronometer, having a hardened and temper- 

 ed balance spring of steel, and having registered its arc of vibration, 

 which was 180°, from the point of rest, we removed this spring, and 

 applied one of glass. The vibrations were immediately increased to 

 an arc of 200°, thus proving that glass had greater elastic force than 

 steel, for the weight of the balance was not disturbed by the applica- 

 tion of the glass spring, and the arc of vibration being increased and 

 the same time preserved, its strength was necessarily equal to the 

 original one. 



Satisfied thus far with our efforts, we took it to Captain Beaufort, 

 the hydrographer to the Admiralty, who promised us his assistance. 

 in obtaining their lordships' order for any trial to which we might 

 wish the experiment to be subjected in our progress. Thus encour- 

 aged, the necessary adjustments for temperature, &,c. were com- 

 menced. 



Two important questions suggested themselves at this early stage 

 of the experiment. The first was to ascertain how far a low tempe- 

 rature would affect the fragility of the glass spring ; and the second 

 was to prove by experiment whether it would withstand the shock 

 arising from the discharge of cannon. 



To determine the first question, we placed the chronometer in a 

 temperature of 12° Fahrenheit. In speaking of this low tempera- 

 ture, it may not be considered as digressing too much to explain the 

 manner in which it was obtained ; and we may be allowed this oppor- 

 tunity of describing our method of procuring a low temperature even 

 during the summer months. The chronometer submitted to the pro- 

 cess is placed in a metal vessel, having a piece of glass in the top, to 

 allow a thermometer in it to be read, and the chronometer to be com- 

 pared. This vessel, which we may call the internal one, is placed 

 in an outer one similarly constructed with a glass top, but having a 

 space completely parted off within it at the distance of an inch and a 

 half from its outer sides; The distance thus left being occupied by 

 common air, prevents the exterior atmosphere from readily acting on 

 the ice which is to be contained within the partition. The inner ves- 

 sel containing the chronometer is then placed in the centre of this 

 outer vessel, and kept in its place by blocks of wood, and the space 

 between it and the partition above-mentioned is filled with ice and 



