236 MESSRS. R. THRELFALL AND J. A. POLLOCK 



Let 6, be the reading corresponding to g. the value of g at Sydney. 

 m g m g Melbourne. 



Q p g p (j any other place. 



We have then 



with corresponding values for m and P . 

 For any one value of t we have 



0. ~ 0* _ 9. ~ 'J, 



fi ft ~"~ n 



or 



0i 0m 



From the reading at any station at any temperature we may therefore determine 

 the difference of g between that station and a standard station, say Sydney ; 

 provided we know the reading at Sydney at that temperature, the difference of 

 reading between Sydney and Melbourne at that temperature and the difference in 

 the values of g at Sydney and Melbourne. 



To get an idea of the numbers involved in the use of our present instrument, 

 we may take the Sydney reading at 21 on October 6, 1898, as 83. We have then 



Reading at Sydney 83, corresponding to g = 979*639, as given by Mr. LOVE. 

 Melbourne 82, g = 979*916, 



the Pole 70*5, g = 983*11, EVERETT'S ' Units and 



Physical Constants.' 



,, the Equator 88*6, corresponding to g = 978*1, EVERETT'S ' Units and 



Physical Constants." 



The readings are those which would be given by our sextant arc, the temperature 

 being 21 C. 



From Equation (2) we get 



Sd mla. sin -Jr 



If St is taken equal to 1 C. on our thermometric scale, we have by observation 



fa 



-j- at Sydney = 31*50 sextant minutes. 



We can at once deduce that 

 and 



- at Melbourne would be 31*51. 

 of 



the Pole 31*61. 



,, Equator 31*41. 



