398 
had its velocity reduced by 36,000* miles an hour ? Moreover, what could 
so reduce its velocity ; or, if reduced, cause it afterwards to increase, so as 
to enable it to get round the flying sun ? 
“ (9.) In conclusion, I would beg D. and others to observe that, at last, 
after a life-long adherence to this ill-considered theory, the Astronomer- 
Royal now admits it to be fraught with doubt and uncertainty and confusion. 
. . . . I, too, was taught, as a child, that even the earth’s whole orbit is 
‘ only as a point,’ with reference to the fixed stars ; but, as a man, I don’t 
believe it.’ Credite posteri ?” 
31. These arguments, as I have said, appeared in the Astro- 
nomical Register , which has a considerable circulation among 
astronomers, but no rejoinder to my last letter appeared either 
from Mr. Dell or any other. In fact, the arguments are un- 
answerable ; and, of course, it is not my duty to account for 
the apathy, or whatever else it may be, among professed astro- 
nomers, who must be supposed to be competent to understand 
the bearings of such reasoning and demonstrations upon our 
current physical astronomy. What is thus true of Jupiter and 
his second satellite, taking the rates of motion assigned autho- 
ritatively to each, is true mutatis mutandis of all the planets 
having satellites, and so it applies to our earth and moon. It 
was to the actual motion of our own satellite, according to the 
current theory,, that I endeavoured to draw the attention of 
the British Association at Bath in 1864, in the Paper I have 
already referred to, and which I afterwards placed in our Vice- 
President’s hands (§ 2). 
32. But here I will only refer to one most important point 
relating to the moon’s motion, as bearing upon the verification, 
which Newton is supposed to have obtained by means of it, of 
the law of universal gravitation. Now, this supposed verifica- 
tion was obtained by calculating the amount of the moon’s 
fall from the tangent to her orbit in a given time. Taking 
the moon’s orbit round the earth as circular or oval, and 
taking the semi-diameter of this quasi- orbit as equal to sixty 
semi-diameters of the earth (i. e. 60 x 4,000=240,000 miles), 
Newton found that the time occupied by the moon in falling 
through a given space was exactly sixty times greater than 
that occupied by a body at the earth’s surface in falling 
through an equal space.” f And so, says Mr. Grant, in 
his History of Physical Astronomy , “ it thus appeared that 
the force which retained the moon in her orbit, as deduced 
* This would be so, if the sun’s motion were at the lowest rate assigned to 
it (by Struve and others) of 18,000 miles an hour. 
t Grant, pp. 24, 25. 
