WCP1394

[1]^1,2,3

16, Earlsfort Terrace,

Dublin.

Nov[ember] 24 1903

Dear Sir

Thanks you for yours. My chief object was to place my views before you for consideration. I make however some remarks on the letter. Having since procured a copy of Newcomb⁴ on the Stars⁵ (which I have only glanced at) I think you will see that your account at [sic: of?] p. 256^6,7 is misleading — at least it & omits the number of large proper motions &c in Auwers's⁸ Zone.

As regards Venus Dr Prof Newcomb says in his Astronomy for Everybody⁹ published in the present year p.171 after explaining the spectroscope method and its difficulty "It was thus [2] found by Belopolsky¹⁰ that the planet was affected by quite a rapid rotation —. On the general fact was made very probable. On the whole we must regard this conclusion as the most likely that has yet been reached although it is at variance with those of Schiaparelli¹¹ as well as those of the Lowell Observatory."¹² The Lowell results referred to here were arrived at by markings but I do not think the Lowell observers rank as high as Belopolsky as spectroscopists. The proper verdict I think is "not proven". Of Mercury Newcomb says (p. 161). "All that a conservative astronomer would be willing to say is that as yet we know nothing of the revolution of Mercury on its axis." I think the dissent from Schiaparelli as regards both planets is on the increase. I doubt if the equatorial protuberance on Venus or Mercury caused by rotation could be measured unless it was greater than in the case of the earth. Venus [3] is a fine crescent when near us and is more remote than the sun when she looks nearly round. And where are we to look for a slight protuberance until we know the position of the axis of rotation? What if the planet did not rotate at all? (Though I do not think any astronomer maintains this).

I think at p 236 you imply that the moon's mass is 1/50 of the earth's. At least what you are dealing with is the quantity of material required to make it. But perhaps the assumption was that the parts of the moon earth which formed the moon had when detached the same density as the moon. I am at a loss however to understand why no water was carried off to the moon in this process — especially if the whole earth was covered with water or aqueous vapour when it took place and the dry land on the earth owes its existence to the formation of the moon having made holes for the water to collect in.

You are right I believe as to Saturn ( I fancy Miss Clerke¹³ wrote on the subject to of Venus's rotation before Belopolsky's observations were known or perhaps made). [4] As to you theory at pp 305 — 310 it is not much in my line. But if there is no solar cluster or that cluster does not assume a ring-shape or there is no gap between it and the Milky Way there are holes in it. Since the discovery of radium the necessity of keeping up a constant supply of solar heat is not so obvious though the presence of radium in the sun is still without proof. But I think if a sufficient number of meteors were drawn into the sun to keep up the supply of heat we should encounter more of them on the way: and those whose orbits we have ascertained seem to be almost always moving round the sun instead of falling into it. (Dr Kleiber¹⁴ I think computed that one shower noticed by Mr Denning¹⁵ about Christmas was actually rushing into the sun but this was only one of some 800 in his Catalogue¹⁶).

I have no doubt that we have got very near the distance of the sun from the earth — one of the most satisfactory methods to my mind being the [5]^17,18 actual measurement of the velocity of light compared with the aberration of the fixed stars. But it would be better not to refer to Eros in a second edition unless the results appear in the meantime.

With regard to the habitability of other worlds I do not think the existence of spectroscopic p binaries proves much. Why may not an inhabited planet revolve round the pair? Two of the earliest-discovered and best-known to spectroscopic binaries have a bright companion revolving round them — Mizar and Castor. Why not a dark companion as well as a bright one? In both cases too there is a third little bright star which seems to belong to the system.

I believe in the existence of life and intelligence outside of the earth but I admit that this is not susceptible of proof. It seems to me very improbable that among the suns which I think cannot number less than a thousand millions ours is the only one which provides [6] the necessary conditions for such life. I think also you have not laid sufficient stress (but on this point you are much better qualified to form an opinion than I am) of [sic] the power of adaptation to changes which animals possess provided that the change is sufficiently slow — which leads me to think that life might have expia originated under any state of things to which animals here might be ultimately and by slow degrees acclimatised y just as the animals which began to exist under these conditions might be [sic] slow degrees be so modified as to be capable of living here. The animals which exist here are suited to terrestrial conditions — otherwise they could not continue to exist. But are we justified in maintaining that the conditions which seem essential to animal and plant life on the earth are essential to it everywhere?

Sincerely yours | W H S Monck [signature]¹⁹ [7]²⁰

P.S. A count which I made of the stars of each magnitude in the Oxford and Harvard Photometries was published in the Siderial Messenger for 1888 but I made the error in the original article (which I corrected in a subsequent number) of taking the theoretical ratio of 2.512 to 1 for the number of ratio of the number of stars of two successive magnitudes as the result ^{on the hypothesis} of uniformity and thus arrived at the conclusion that the stars were thickening not thinning at the outset. But my ratios are considerably less that 3.5 to 1. Here they are

(Over) [8] (I don't know why I selected the 9^s instead of the even numbers or whether I did not mean the latter)

	Harvard	Oxford
Brighter than 1.9	24	22
1.9 to 2.9	65	48
2.9 to 3.9	195	142
3.9 to 4.9	654	400
4.9 to 5.9	2009	1351

The Harvard measures went farther South and covered a larger part of the sky. You will see that there is not a single instance in which the ratio reaches 3.5 to 1. (Between the first two the theoretic ratio is 3 to 1 not 4 to 1 but it is not attained ).

WHM [signature]