270 Mathematical Theories of the Earth. — Woodward. 
meridional arc in France gave color to the false theory and furnished 
one of the most conspicuous instances of the deterring effect of an 
incorrect observation. As you well know, the point was definitely 
settled by Maupertuis's measurement of the Lapland arc. For this 
achievement his name has become famous in literature as well as in 
science, for his friend Voltaire congratulated him on having "flattened 
the poles and the Cassinis," and Carlisle has honored him with the title 
of "Earth flattener." 
Since the settlement of the question of the form, progress towards a 
knowledge of the size of the earth has been consistent and steady, 
until now it may be said that there are few objects with which we have 
to deal whose dimensions are so well known, as the dimensions of the 
earth. But this is a popular statement, and like most such needs to 
be explained in order not to be misunderstood. Both the size and 
shape of the earth are defined by the lengths of its equatorial and polar 
axes ; and, knowing the fact of the oblate spheroidal form, the lengths 
of the axis may be found within narrow limits from simple measure- 
ments conducted on the surface, quite independently of any knowl- 
edge of the interior constitution of the earth. It is evident in fact, 
without recourse to mathematical details, that the length of any arc, 
as a degree of latitude or longitude, on the earth's surface, must 
depend on the lengths of those axes. Conversely it is plain that the 
measurement of such an arc on the surface and the determination of 
its geographical position, constitute an indirect measurement of the 
axes. Hence it has happened that scientific as distinguished from 
practical geodesy has been concerned chiefly with such linear and 
astronomical measurements, and the zeal with which this work 
has been pursued is attested by triangulations on every continent. 
Passing over the earlier determinations as of historical interest only, 
all of the really trustworthy approximations to the lengths of the axes 
have been made within the half century just passed. The first to 
appear of these approximations were the well-founded values of Airy, 
published in 1830. These, however, were almost wholly overshadowed 
and supplanted eleven years later by the values of Bessel, 
whose spheroid came to occupy a most conspicuous place in 
geodesy for more than a quarter of a century. Knowing as we 
now do that Bessel's values were considerably in error, it 
seems not a little remarkable that they should have been so 
long accepted without serious question. One obvious reason is 
found in the fact that a considerable lapse of time was essential for 
the accumulation of new data, but two other possible reasons of a 
different character are worthy of notice, because they are interesting 
and instructive whether specially applied to this particular case or 
not. It seems not improbable that the close agreement of the values 
of Airy and Bessel, computed independently and by different methods, 
— the greatest discrepency being about one hundred and fifty feet, — 
may have been incautiously interpreted as a confirmation of Bessel's 
