438 
appears to move in a circle round the earth, is no longer really a circle, but a 
slightly irregular arc, crossing and re-crossing, and nearly corresponding with 
an arc of about 30° of the earth’s annual orbit round the sun. The moon’s 
apparently circular monthly orbit round the earth is now but a mere appear- 
ance, resulting from her varying velocities as she thus crosses and re-crosses 
the path of the earth, always moving with decreasing speed as she approaches 
the sun from full moon till she is in conjunction, and always increasing in 
velocity as she recedes from the sun between new moon and till she is full ; 
her velocity being always least while she dips within the orbit of the earth, 
and greatest when she is moving outside, or beyond the earth’s orbital 
path. 
11. I call attention to these details and dwell upon them, not as advancing 
anything that is absolutely new,— though I know they will appear as such to 
many, but because they have been too much or altogether disregarded, and 
have not been duly weighed, nor truly represented, in the explanations or 
interpretations of the phenomena of the moon’s motion hitherto put forth, 
and now generally accepted. 
12. Some, at least, of these facts as to the moon’s real path and varying 
velocities will be found recognized in the following passages, which I cite 
from the ninth edition of Ferguson’s well-known work on Astronomy. Having 
drawn a diagram to scale of the earth’s and moon’s relative paths in their 
respective orbits round the sun, he says : — 
“ Thus we see that, although the moon goes round the earth in a circle with 
respect to the earth’s centre, her real path in the heavens is not very different 
in appearance from the earth’s path. . . . The moon’s absolute motion 
from her change to her first quarter is so much slower than the earth’s, that 
she falls 240,000 miles (equal to the semi-diameter of her orbit) behind the 
earth at her first quarter ; that is, she falls back a space equal to her distance 
from the earth. From that time her motion is gradually accelerated to her 
opposition or full, and then she is come up as far as the earth, having regained 
what she lost in her first quarter. From the full to the last quarter her 
motion continues accelerated, so as to be just as far before the earth as she 
was behind it at her first quarter. ' Afterwards her motion is retarded, so 
that she loses as much with respect to the earth as is equal to her distance 
from it. . . . Hence we find that the moon’s absolute motion is slower 
than the earth’s from her third quarter to her first, and swifter than the 
earth’s from her first quarter to her third, her path being less curved than 
the earth’s in the former case, and more in the latter. Yet it is still bent the 
same way towards the sun,” or (as he again shows by the diagram drawn to 
scale) “ is concave to the sun throughout.” (§§ 266, 267.) 
13. These brief citations from Ferguson’s Astronomy show, that the 
hypothetical facts to which I appeal, have been substantially recognized by 
astronomers, and are not really new, though they have been too much or 
almost altogether disregarded, and although what flows from them has been 
overlooked. As an instance of this, I beg leave to refer once more to the 
Astronomer Royal’s Six Lectures on Astronomy. The author is speaking of 
the deceptiveness and frequent unreality of mere appearances, as regards 
rest and motion ; and, arguing in favour of the heliocentric theory, he 
says 
“ The argument is precisely the same as applied to the heavens. If we 
had nothing but the sun and moon turning about in various ways ; even 
then, remarking their great size and their great distance, and the great 
speed with which they must be supposed to turn (for the moon must be 
supposed to move at the rate of 60,000 miles an hour, and the sun very much 
quicker), their daily revolution round the earth would be very unlikely.” 
(4th ed , p. 54.) - 
