284 Variation in the Obliquity of the Ecliptic. [July, 
the poles of the earth was that the protuberance of the 
earth about equatorial regions was a¢ted on by the sun and 
moon, and caused the dire¢tion of the earth’s axis to vary, 
though the pole of the earth traced always, it was supposed, 
a circle round the pole of the ecliptic as a centre. 
When the accuracy of modern observation proved that 
there was a constant decrease in the obliquity of the ecliptic, 
at the rate of about 0°45” per century, there seems to have 
been a great lack of geometrical knowledge among the 
astronomers occupying official positions, for they still wrote 
of and described the movement of the pole of the heavens, 
as tracing a circle round the pole of the ecliptic as a centre, 
and never varying its distance from this pole, yet admitting 
that there was a decrease in the obliquity of 0°45 per 
annum. Now the fact is, that any variation in the obliquity 
is the same thing as a variation in the angular distance of 
the pole of the heavens from the pole of the ecliptic, and of 
the circumference of the circle from its supposed centre, 
consequently that the pole of the heavens can describe 
a cirycle round the pole of the ecliptic as a centre; whilst we 
admit a decrease in the obliquity is granting as true that 
which is impossible. That a grave oversight was here 
committed it is useless to deny; and though many official 
astronomers have, since we pointed out* this error, attempted 
to defend their predecessors, or their own writings on this 
erroneous problem, yet their endeavours partake more of 
the attempts of advocates to defend a bad cause than of 
philosophers desirous of eliciting truth. Personal attacks 
on an author who has pointed out their errors, and assertions 
that his problems are by no means believed in by A, B, or C, 
are not proofs of error, nor can any amount of “ authority ” 
outweigh a geometrical proof or law. 
When a certain school of teaching have agreed to some 
problem or theory, have written on this as if it were un- 
questionable, and have based their calculations on it, it 
naturally follows that they should at first oppose any inno- 
vation on their belief. It does not follow, however, that any 
number of such men, if they merely make assertions, should 
carry one atom of weight in disproving that which can be 
demonstrated by mathematics or geometry. What weight, 
for example, does Herodotus carry when he asserts that he 
cannot refrain from laughing when he hears men state that 
the earth is round, as though made in a machine, and that 
Asia is as large as Europe. He then asserts the relative 
* In the “ Last Glacial Epoch,” and ‘‘ The Proper Motion of Fixed Stars.” 
