316 : LAPLACE. 
ceived that the earth, if it was originally fluid, ought to 
bulge out at the equator. Huyghens and Newton did 
more ; they calculated the difference between the greatest 
and least axes, the excess of the equatorial diameter over 
the line of the poles.* 
The calculation of Huyghens was founded upon hypo- 
* It would appear that Hooke had conjectured that the figure of 
the earth might be spheroidal before Newton or Huyghens turned 
their attention to the subject. Ata meeting of the Royal Society on 
the 28th of February, 1678, a discussion arose respecting the figure of 
' Mereury which M. Gallet of Avignon had remarked to be oval on the 
occasion of the planet’s transit across the sun’s disk on the 7th of 
November, 1677. Hooke was inclined to suppose that the phenomenon 
was real, and that it was due to the whirling of the planet on an axis 
“which made it somewhat of the shape of a turnip, or of a solid 
made by an ellipsis turned round upon its shorter diameter.’’ At the 
meeting of the Society on the 7th of March, the subject was again 
discussed. In reply to the objection offered to his hypothesis on the 
ground of the planet being a solid body, Hooke remarked that 
“although it might now be solid, yet that at the beginning it might 
pave been fluid enough to receive that shape; and that although this 
supposition should not be granted, it would be probable enough that 
it would really run into that shape and make the same appearance; 
and that it is not improbable but that the water here upon the earth might do 
it in some measure by the influence of the diurnal motion, which, com- 
pounded with that of the moon, he conceived to be the cause of the Tides.” 
(Journal Book of the Royal Society, vol. vi. p. 60.) Richer returned 
from Cayenne in the year 1674, but the account of his observations 
with the pendulum during his residence there, was not published 
until 1679, nor is there to be found any allusion to them during the 
intermediate interval, either in the volumes of the Academy of Sci- 
ences or any other publication. We have no means of ascertaining 
how Newton was first induced to suppose that the figure of the earth 
is spheroidal, but we know, upon his own authority, that as early as 
the year 1667, or 1668, he was led to consider the effects of the cen- 
trifugal force in diminishing the weight of bodies at the equator. 
With respect to Huyghens, he appears to have formed a conjecture 
respecting the spheroidal figure of the earth independently of Newton; 
but his method for computing the ellipticity is founded upon that given 
in the Principia.— Translator. 
