426 
and Ferguson’s mechanical illustrations, and show their inapplicability, by 
supposing (instead of motions in the cabin of a vessel) you have two separate 
steam-vessels attached to one another by a rope ; and first suppose one of 
them to be at rest, and the other to steam round it at the rate of two knots 
an hour ; that will give the string a certain tension which may represent 
gravity ; but if you start off the stationary vessel at ten knots, what would 
be the effect ? It would then drag the other after it, the tension on the rope 
only being lessened pro tanto by the two knots at which the other was 
steaming. But in order that the latter should now steam round the former 
as before, it must sometimes steam twelve knots an hour in the same 
direction ; and even when appearing to go the other way, it must be steam- 
ing eight knots, and still in the same direction. But I say that you could 
not have two free bodies thus held together by attraction — one going 
steadily at ten knots, and the other sometimes at twelve knots, some- 
times at eight knots an hour, — and that there is no attempt at 
demonstrating anywhere that such a thing is dynamically possible. 
If the bodies were mechanically attached by ropes or rods, that would 
be another matter, though even then you would require a “law” other 
than attraction to explain these greatly varying velocities. Therefore. 
I say the moment you adopt the theory of solar motion in space you 
upset Newton’s Principia. But Mr. Brooke has not alluded to the fact that 
the Astronomer Royal himself has now given up this theory. And it is no 
answer to the objections I have urged against current physical astronomy to 
say that I furnish you with no theory to take its place. I might rather 
take credit for that. And, at any rate, you cannot believe a thing which is 
proved to be untenable, merely because you cannot properly account for the 
phenomena in some other way. It is better and simply honest in such 
circumstances to say that we do not know, when in sober truth we are in 
ignorance. 
The Chairman. — So far as I have read Mr. Reddie’s works, he has 
answered the popular explanations of such men as Airy, Herschel, and others, 
rather than the purely scientific part of the question. The interpretation of 
the differential equation is of that kind that it is impossible to bring it 
before the popular mind except by rough illustrations. The popular lectures 
on gravitation by Airy, are just an attempt, by a rough kind of illustration, 
to give some kind of idea of what would be the motion of the heavenly 
bodies according to Newton’s system of gravitation. There is no rigid de- 
monstration in them. Men like Michell have simply copied what was written 
by Airy and Herschel. As I have already said, the way in which physical 
astronomy is to be attacked, is either by showing that the differential equa- 
tions depend on unsound assumptions, and that the calculations made by thei r 
aid, of a series of complicated phenomena, are not to be relied on ; or else 
that those complicated phenomena do not agree with mathematical demon- 
stration, or that they can be explained in some other way. 
Mr. Reddie. — It is too late now to renew the discussion, and I was not 
prepared for a second attack after having made my reply. I beg to be 
