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cised upon her by the sun. And, not only so, but the very direction of her 
motion is also reversed by this fictitious hypothesis, as exhibited in fig. 59 of 
the Lectures. Every astronomer must know that the moon’s real motion is 
always direct. (Tide Ferguson's Astr., in loco.) In fig. 59 of the Lectures 
her path is represented as retrograde , when in conjunction and between her 
last and first quarter ; as going, in short, at the rate of 2,288 miles an hour 
to the right, in a path greatly curved and convex to the sun, when in reality 
she is moving to the left, in a totally different curve, which is concave to the 
sun, and then she is so moving with thirty times greater speed than the 
2,288 miles an hour assigned to her in the Lectures. 
I had the honour to forward to you, in 1862, a paper entitled The 
Mechanics of the Heavens , which I had that year laid before the British 
Association at Cambridge ; in § 11 of which paper, and the foot-note p. 6, I 
have expressed all I care to say as regards the difficulty, which I am quite 
aware there often is, in obtaining a hearing from eminent men like yourself for 
communications such as this. I beg leave only to add that I, nevertheless, 
think it a duty, from which I will not shrink, and also an act of courtesy on 
my part, to send you this letter, whatever may be its reception. But should 
I be favoured with any answer, I would beg that, whatever may be its nature, 
I may be permitted to publish it along with what I have now, most respect- 
fully though freely, ventured to address to you as the Astronomer Royal of 
England. 
I have the honour to be, Sir, 
Your very faithful, humble Servant, 
J. REDDIE. 
To George Biddell Airy, Esq., F.R.S., F.R.A.S., &c. &c., 
Astronomer Royal, Greenwich. 
P.S. — To save you all unnecessary trouble, should you now be pleased to 
bestow any attention on this matter, I shall forward by book post, along with 
Victoria Toto Gcelo , another copy oi The Mechanics of the Heavens , and also 
of Vis Inertias Vida ; or, Fallacies affeding Science, which is frequently 
referred to in both the others, as it is probable you may not have cared to 
preserve those previously forwarded to you. 
[ Answer to the above Letter.] 
Royal Observatory, Greenwich, London, S.E., 
June 7th, 1864. 
Sir, — I am obliged by your courtesy in sending me three pamphlets, and 
by the trouble which you have taken in your letter of June 6, in indicating 
certain points to which you wish to call my attention. 
I cannot at any length enter into the matter ; but I will merely observe 
that much of what you say is quite correct, but that the difficulties which 
you have founded thereon are incorrect. It is true that the earth and the 
moon are two independent planets circulating round the sun, but under 
circumstances which make their perturbations excessively large, so large as 
to give the appearance or relative fact of the moon circulating round the 
earth. It is true that the moon as a planet has the large velocity round the 
sun of which you speak. But it is also true that, inferring relative forces 
from the difference of absolute forces (which on mechanical principles is 
perfectly correct), and inferring relative motions from the difference of 
