THE INFLUENCE OF DISTURBING ACCELERATIONS ]37 



It is clear that the Brown correction will equal 



a^a/^_a/^ (38) 



^ 4>g 4>g 



As was shown above a^ may be recorded by taking readings of the instru- 

 ment which register the amplitude of its forced oscillations. 



The special reservation should, however, be made that in practice the 

 horizontal and vertical acceleration components on vessels are far from 

 being identical. If the influence of the accelerations on the gravimeter readings 

 is to be more strictly accounted for, an especial measurement of the horizontal 

 accelerations by one of the methods currently in use in pendulum observations 

 becomes necessary. 



CONCLUSIONS 



In closing, the main conclusions can be briefly forinulated. 



1. It is not necessary to wait for total abatement of the instrument's 

 beam when taking readings with a damped marine gravimeter. The reading 

 for a position of static equilibrium can be calculated from the record of the 

 gravimeter pendulum and this considerably curtails the time required for 

 observations at the point. 



2. The basic parameter of the gravimeter (for a given oscillatory frequency 

 of the vessel)— the dynamic coefficient — can be derived from the recorded 

 motion of the instrument's pendulum. 



3. When the instrument's pendulum is strongly damped small sinusoidal 

 vertical accelerations only evoke sinusoidal forced oscillations in the pendulum, 

 the amplitude of which is proportional to the value of the dynamic coefficient. 



The amplitude of the vertical accelerations is arrived at from the record 

 of the oscillations of the gravimeter pendulum. Having allowed for the 

 existence of the relation a^^ = a^-V aJ' we can find the value of the Brown 

 correction from the recorded oscillations of the gravimeter alone. 



The accelerations and rotatinal movements of the Cardan suspension 

 must be registered if there is uncertainty as to the satisfaction of the equality 



4. A period of natural oscillation of the Cardan suspension considerably 

 greater than the period of the vessel's oscillations is selected in order to 

 diminish the influence of the horizontal accelerations. 



In this connection it is undoubtedly advantageous to use gyroscopic 

 stabilization for the position of the gravimeter. 



The gyroscopically stabihzed Cardan suspension is treated in this case 

 as a Cardan suspension with a very large period of natural oscillation. It is 



