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Mr. Brooke. — It is easy to calculate the time which the undulations of 
light emitted from a particular star take to reach the earth. 
Admiral Fishbourne. — Supposing the light has been travelling in space 
for one hundred years, and he wants to get the position of the star at the 
moment when he takes the observation ? 
Mr. Brooke. — The position of the star bears the same relation to the 
earth and the moon and surrounding objects as it did yesterday or a hundred 
years before. 
Dr. Irons. — I think it is important that we should know whether the 
calculations with which the public mind is familiar — those which produce a 
knowledge of eclipses — are really to be made on the old Ptolemaic theory. 
The Chairman. — I do not think Mr. Brooke or any other gentleman can 
contradict my assertion. Our books on physical astronomy are open to 
everybody ; and you will find that, so far as the lunar theory is concerned, it 
is calculated according to the Ptolemaic theory. (Mr. Red die, — Hear, hear.) 
All our mathematical demonstrations of the lunar theory go upon the as- 
sumption — the convenient assumption — of the Ptolemaic theory. The plane- 
tary theory, however, assumes the sun as the centre of the system, and gives the 
strongest probability to the Copernican. — I now call on Mr. Reddie to reply. 
Mr. Reddie. — In the first place, I must observe, with reference to the 
criticism upon the title of my paper, that I differ, of course, from you, sir, 
with great deference, and very unwillingly. But still I must defend the 
title of my paper. According to all the books on astronomy with which I 
am acquainted, what you have been speaking of as physical astronomy is 
usually called “ practical astronomy.” Leaving this, however, I am extremely 
obliged to you for what you have said in answer to some of the remarks of 
Mr. Brooke, especially as to the calculation of eclipses. But you have not 
answered him completely. Eclipses were calculated not only long before 
Newton’s time, but before Copernicus, and I might even say before Ptolemy ? 
in Egypt, India, and China. Long before they were known to the observa- 
tions of astronomers in this country or in Europe, they were known to the 
astronomers among the ancients ; and eclipses were not only accurately 
calculated, but critical chronology actually rests upon those calculations and 
observations. As to the modern mode of making such calculations, of course 
I am extremely obliged to the Chairman for so completely answering the first 
part of his speech by his later remarks. (Hear, hear.) He has told us of the 
extremely convenient “ devices” or “ tinkering” which are had recourse to, 
and it is no doubt extremely convenient, when you are out a little in your 
theoretical calculations, to be able to add something to make you right. 
And, in fact, this is an admission that these calculations prove nothing, 
being vulgarly what we call “ dodged.” But I venture to say that the main 
points I have thrown out in my paper for discussion have not been really 
met. (Hear, hear.) Mr. Brooke has chiefly noticed what may be regarded 
as merely incidental points, which, for that reason, I almost now regret I 
introduced into my paper. And yet they are of importance in their proper 
place. As regards action and reaction 
