WCP2802

[1]

38 L^r Baggot St

Dublin,

Feb. 25, 1901

Dear Sir,

I have seen your two letters¹ to Prof. Barret² in one of which you say you would like me to write to you on the subject which you are considering. I am sorry to say that I can render very little assistance in the matter as I am quite an agnostic concerning it. The conditions of a nebula are so far from anything that [2]³ can be reached in laboratory experiment that it seem [sic] to me to be, at present, at least, useless to speculate on what might happen in a nebula. I have myself been exercised on the very point which is engaging your attention.

Prof. Barrett seems to have urged upon you the spectroscopic evidence for the nebulous condition of a so-called nebula you have partially answered him by pointing out that the collisions of your meteors would produce heat and gases. But [3] the incandescent meteors w^d. give a continuous spectrum on which the gaseous spectrum w^d. be superposed. But I believe that there are many nebulae without the least sign of a continuous spectrum. How they can keep so puzzles me as much as yourself. It is now a rather general belief that electricity plays a large part in producing some of the phenomena of comets. Comets no doubt are very differently constituted from nebulae and it is easier to conceive that electricity should be more active with them than with nebulae [4] so that we cannot, of course, argue from one to the other. But it seems allowable to think that electricity may be concerned in some way with the nebulae or perhaps even some agency of which we are ignorant. This last is I confess a very cheap and easy mode of settling difficulties. Some reasonable persons have thought it quite possible that the unit of gravitation may not be so the same throughout the universe[.] It would be reasonable for such persons to think that there might be other differences between our part thereof and [5] others so vastly distant.

Prof. Barrett tells me that he suggested to you that he great internal commotion and shifting of the parts of a nebula might explain your difficulty. This would fall in with the idea of Laplace⁴ who supposed that there was this kind of commingling of parts in the rings whence the planets were formed according to his theory. He supposed that there was such internal commotion in each ring that its outer and it inner edge would have about the same angular velocity [6] about the sun that it is to say that the linear velocity of the center edge would be greater than that of the inner. He saw that if the outer and the inner parts of a ring were simply revolving round the sun on each on its own account (as unquestionably obtains with the rings of Saturn) the inner parts must be revolving round the sun with a greater velocity both linear and angular than the outer and that therefore if a ring broke into portions which [7] would afterwards coalesce to form the planet each portion would have a retrograde rotation and so would the formed planet itself — which is contrary to fact. Prof. Barrett and Laplace are ^both driven to have recourse to internal commotion; but for quite different reasons.

Laplace's nebular hypothesis is questioned by able men for various reasons chiefly as far as I know dynamical ones some of such believe that the separation of the planets w^d begin in the middle of the [8] of the solar system nebula instead of at the outside as L. would suppose. I have seen more than one new version of the nebular hypothesis in the Comptes Rendus of the French Academy a good many years ago. The famous Nebula in Andromeda which used to be regarded as such a striking confirmation of L.'s hypothesis is shown by Roberts⁵ to be a spiral nebula; and those spiral nebulae seem to be great stumbling-blocks for L.

Yours very truly | M H Close⁶ [signature]