WCP2928

[1]¹

OBSERVATORY,

CAMBRIDGE.

4 Mar [19]09

Dear D^r Wallace,

I have answered your questions as well as I can. The best book is "Newcomb's Popular Astronomy"

The honours that you have been receiving has afforded much pleasure to your many friends among whom I am proud to think is numbered[.]

Yours very truly | Robert S Ball [signature]

[2]

Question I

"If gravitation is universal in the visible Universe, must not all molar motions of the larger aggregations of matter (light and dark suns) be produced and regulated by gravitation"?

Answer

There is no doubt that all the molar motions are regulated by gravitation but I would not like to say they were all produced by gravitation. Newton’s First Law of Motion tells us that a body not acted upon by any force will, if once moving, continue to move uniformly in a straight line forever. Of course motions may origiante in other ways besides gravitation as for example by explosion. Indeed the first law of motion is quite independent of gravitation.

[3]

Question II

"If so, has it been shown to be possible, for any star to acquire much rectilinear motion as to take it through and across the whole stellar universe"

Answer

Assuming the mass of the stellar universe to be finite it is quite possible to conceive a body having a velocity sufficiently great to carry it clear away from the stellar systems. The star Groombridge 1830 is moving with a velocity of 200 miles a second and Newcomb showed that even with a very liberal assumption as to the mass of the sidereal[?] system gravitation could not stop this star's flight. It seemed destined to pass away to an indefinite distance[.]

[4]

Question III

"Is such a rectilinear motion conceivable, even, under gravitation"?

Answer

There does not seem to be any limit to the velocity attainable by a star short perhaps of the velocity of light itself. A star has been known to move at the speed of 900 miles a second. The new star Nova Persei gave rise to a nebula in which motions were seen exceeding 100,000 miles a second. It is however proper to add that some persons hold that this movement was not exactly a transference of matter in the ordinary sense. There are however no physical objections so far as I know to bodies actually moving with the velocity I have named[.]

[5]

Question IV

"Must not (under unusual gravitation) the motions of all stars that are in each others vicinity, be differential, not independent of each other; so that as they approach each other, it must be by spiral or other curves of excessively slight curvature, and thus require myriads of ages to come into actual collision".

Answer

It is I believe quite true that the motions of all bodies in the universe are connected together to some extent and it is also true that collisions of celestial bodies are exceedingly rare on account of the enormous distances. As however the celestial bodies are so excessively numerous collisions do occasionally happen and become manifest in the appearance of a new & temporary star[.]

[6]

Question V

"Lastly, is the present view of many astronomers, that the visible universe consists of two systems of stars, moving in opposite directions and independent of each other, a demonstrated fact; or may not the appearances be consistent with gravitational motions"

Answer

I believe all the appearances in the celestial motions are quite consistent with the law of universal gravitation and this is the case whether we accept the view of the general division of the universe into two systems of stars moving in different directions or whether we reject this view I must say that so far as I can judge the Two-system theory has not been proved but in any case the supremacy of gravitation remains unquestioned[.]

[7]

Sir Robert Ball's

Replies to Questions

March 7th 1909