344 SECTION MECHANICS. 



of friction. For friction meaning retardation, in other words a check- 

 ing of the action of the balance. The oscillation falling off at the 

 same time, and the balance moving rather faster in consequence the 

 tendency to lose is corrected. 



It would appear that this plan of leaving the chronometer fast in 

 the short vibrations also answers as a barometric compensation. For 

 instance, we took a chronometer which was going exactly right at the 

 normal atmospheric pressure and placing it under the receiver of an 

 air pump reduced the pressure to about 1 5 in. Before the pressure 

 was reduced the balance was swinging about 214 from rest, but in the 

 thinner atmosphere it rose to 270", and yet the time of the chrono- 

 meter did not vary more than three-tenths of a second a day the 

 tendency to gain by the removal of the friction due to the denser 

 atmosphere being corrected by the tendency to lose during the longer 

 oscillations. 



The advantage due to the power of isochronising the long and short 

 arcs of oscillation, and the mechanical superiority of its escapement 

 over any clock escapement ever yet invented, almost place the chrono- 

 meter alongside of the best astronomical clocks. 



In conclusion, allow us to remind you that there is a fundamental 

 distinction between a clock and chronometer the time-measuring 

 power of the one depending upon gravity, the time-measuring power 

 of the other depending upon the elasticity of its balance spring 

 that is to say, upon a property of matter. The chronometer is there- 

 fore much more absolute in its measurement of time than the clock, 

 and if for no other reason every effort should be made towards bring- 

 ing it to that perfection which would render it available for the highest 

 astronomical purpose. 



The PRESIDENT : Mr. Glasgow, the representative of the British 

 Horological Institute, wishes to add to the information given to us 

 just now, and although the time for adjournment has arrived I am sure 

 you will be glad to hear him. 



Mr. GLASGOW : I must apologise for coming before you at so late 

 an hour when I had no previous idea of saying anything, but I thought 

 it would be well as there is such an opportunity, and as the subject is 

 of such general interest to the public, that I should carry the matter a 

 little further than Messrs. Dent have done. The rather restricted 



