for the Registration of the Mean Atmospheric Pressure. 437 



tt; tt/ 2*7r 2 sin 2 <x /rkT , T v \ /T ,. 



H'=H(cosa+ — j^ — (2F -L )J, . . (F) 



of which equation 6 of the paper is a particular case. 



4. Simplification of the Formulae by particular adjustments. 



If we make 2F =L ; that is to say, if we so place the siphon 

 barometer that the normal position of a point midway between 

 the surfaces of the mercury in its two legs shall be the centre of 

 suspension of the pendulum, then equation 1 becomes 



A.H-« o7o .^. ' 



Now 



\ + AA, --~X7"~" X~ ~V~ «o 9 ' 

 consequently 



A.H*=-4/ o7o .^l (G) 



Should the mean oblique barometric height be known approxi- 

 mately previously to the construction of the pendulum, let this 

 first approximate value be taken for the normal oblique height 

 H , and let the weight and the centre of gravity of the pendulum 

 be so adjusted that 



H 2 =4/ 7o; 

 then we shall have 



H * " «o* ' [ ' 



and the following formula will be very nearly exact, 



AH=-2^. ...... (K) 



n 



So that a second and very close approximation to the mean 

 oblique height, when the adjustments above described have been 

 made, may be found by the following formula, 



m.H=H (i-|») (L) 



As the correction for centrifugal force in this case disappears, 

 equation 6 is reduced to 



tU.H'=m.Hcosa (M) 



