78 0. E. SCHIOTZ. [NORW. POL. EXP. 
much greater, and the increase in the acceleration will amount on the whole 
to about 0°65 mm. or 0°58 mm. more than in the middle of the continent. 
The influence will continue to increase until a distance of about 20 km. from 
the coast-line is reached. If, as mentioned above, we disregard the slope of 
the continents towards the ocean depths, and imagine them abruptly cut off, 
the influence of the added masses will diminish rapidly towards zero with a 
still nearer approach to the coast-line. On the very boundary between land 
and sea therefore, the acceleration in this case, as indicated above, will be 
about normal. 
If we go out upon the sea, it is easy to see that the acceleration must 
show a decrease as the distance from the coast-line increases, so that at the 
same distance from the margin out there, the acceleration will prove to be about 
as much diminished as it was increased upon the continent. For if we imagine 
the land spread over the whole earth. the influence of the added masses on 
every external point will be zero. If, therefore, we add to the given masses 
the added masses of a continent such as this, extending over the whole earth, 
the influence on external points will not be altered. If we now assume that 
the density of the added masses of this continent is equal and opposite to 
the density of the added masses in the given continent, it is evident that the 
influence of our continent upon external points is equal to the influence of 
a continent occupying the place of the ocean, but with added masses whose 
density is equal and opposite to the density in the added masses ‘of the 
continent. Out on the sea, we can consequently consider ourselves as being 
near the margin of this negative continent, and therefore the influence upon 
the acceleration will be the reverse of the influence on the actual continent, 
and about as great, if the radius of the circumscribing coast-line is not 
too short. 
The continents, however, do not terminate abruptly. The added masses 
on the slope and in the base beneath it will somewhat modify the change of 
the acceleration. When the slope nearest land is very gentle, as is generally 
the case, it will have very much the same effect as a continuation of the 
continent itself, and therefore in the above deduction we must reckon the 
coast margin from the place where the rapid incline towards the ocean depths 
commences. The added masses on this incline will act as a check upon the 
above-mentioned decrease in the value of the acceleration when the land- 
