3 
1257 years the earth's orbit had increased by a ten days' 
journey round the sun, explained by annexed figures from 
Captain Drayson's Book (" The Earth we Inhabit" p. 50). 
By the addition of a day to the year of every leap year, and 
the precession of the equinox, the increase of the earth's 
orbit is not noticed, otherwise in the course of years, 
Christmas would occur in July.* (See Plate I, Fig. 1.) 
The acceleration of the Moon's mean time, or that the 
Moon's motion has been growing swifter from century to 
century, is very simpty explained by Captain Drayson. 
While Sir J. Herschel says " This remarkable fact had long 
" been the subject of toilsome investigation to geometers. 
" Indeed, so difficult did it appear to render any account of, 
" that some were on the point of again declaring the theory 
" of gravity inadequate to its explanation ; others were for 
" rejecting altogether the evidence on which it rested, 
" although quite as satisfactory as that on which most his- 
" torical events are credited." This, however, is readily 
explained by the accompanying diagram. (See Plate I, 
Fig. 2.) 
In the measurements of distances of the earth's surface, 
such as base lines, the later admeasurements are always the 
greater, i.e., with the best instruments and by such men 
as Colonels Colby, Mudge, Snell, &c. (See pp. 20, 68, 
and 90.) 
Differences of latitudes of places as determined by astronomical 
observation and by admeasurement do not agree. Latitude of 
Pisa by measurements from Florence 43° 43' 19", 4, ditto by 
observation of 504 stars, 43° 43' 11", 7, or 7", 6 less by 
* For the earth moves through 360° in 365 days, .*. 59' 1" per day. If, 
therefore, the precession of the equinox = 50" annually, the earth does not 
complete its annual revolution around the sun hy ahout 20 minutes of time, 
this would cause about one day's difference in 72 years, when the precession 
ceased. 
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