PAPERS OX CHEMISTRY AND PHYSICS 2S9 



THE DETERMIXATIOX OF ^'g" 

 A. C. LoxGDEx. Kxox College 



It is not the object of this paper to present a new 

 method or even to consider exhaustively the older meth- 

 ods of determining ''g". That "\»ould reqnire more time 

 than I have at my disj)Osal. TThat I hope to do is to in- 

 dicate a way of getting better results from one of the 

 well known methods. 



Of the various methods of determining ''g", the sim- 

 ple pendulimi method is doubtless the most widely used, 

 and perhaps, all things considered, the most generally 

 satisfactory. 



I think it is the method which succeeds best in the 

 hands of our students, and I also think it has within it 

 the possibilities of great precision. 



The quantities to be measured are two in number, the 

 length of the pendulum, 1, and the period, or half period, 



?T-i 

 t, in the formula g = — 



t= 



The length of a pendulum about a meter long can easily 

 be measured to witliin one part in ten thousand, with a 

 good catbetometer, if the pendulum is properly construct- 

 ed, and if suitable corrections are made for the mass of 

 the suspension and for the moment of inertia of the ball. 

 If, then, the j^eriod can be determined ^-ith equal accu- 

 racy, we should have no difficulty in getting the fourth 

 figure in the final value of ''g". 



The period, however, must be squared and must there- 

 fore be determined to within one part in twenty thousand, 

 in order that the value of ''g" may be correct to within 

 one part in ten thousand. 



To count twenty thousand oscillations and guarantee 

 the count Avould be rather too gi'eat a strain on human 

 endurance, even if we could get a pendulum to continue 

 swinging long enough, which would be another difficulty. 



The coincidence method furnishes a perfectly splendid 

 way of supplementing human endurance at this point, 

 but our next difficultv lies in the fact that the oscillations 



