^zj. Art. 7. — K. Terazawa : 



disturbance of gravity, may be computed l)y our formula. If we 

 suppose the place of the observation not to be very near to the 

 circular basin, the effect, as we see from the above diagram, is of 

 course small, but it increases repidly as the edge is approached. 



For the water-level measurement, the efïect of a material 

 loading will appear in the form ^ + ^, instead of ^ only, where 'P is 

 due to the attraction exerted by the material loading and ^ to the 

 deformation caused by its weight. 



For example, suppose the radius of the North Atlantic basin 

 to be 2000 km, the position of Chicago to be 3000 km from the 

 centre, and the level of the water in this area to be raised one 

 metre, then 



-Z^ = 1-5, q, =0-00255. 



a 



aa^^^-'^y-r^, \ = 0-8639. 



Further assume that the density of sea water is unity and in c.g.s. 

 ;- = 0-65 X 10-^ = 980, 



^dt^^ = jL, /. = 6 X 10", 



then we shall have 



y'' = 1-17x10-« = 0"-0024, 

 Ç ^ .^siTxlO-« == 0"-00(39, 



accordingly the total effect amounts to 



<pj^cr = 4-54x10-« = 0"-009. 



It will be noticed that the effect of tilting is about three times 

 as great as that of tlie attraction, so far as the material constants 

 are assumed as abo\'e. According to Lord Kelvin,'^ who 

 initiated these investigations, tlie direct lunar effect on the 

 deviation of a plumblinc is a maximum when the moon is at the 



1) Xatural Philosophy, Part II. p. 383. 



