Jan. 29, 1880] 



NATURE 



3or 



and I v. i.-h to inake out a perfect vindication, hoping never 

 again to be obliged to recur to it. If you will refer to my 

 reply to Peters, you will see that I speak of our difference in 

 R.A. and stop, coming to a full pau*e. I then take up the 

 subject of Dee., and when through with that, make another 

 period. Then I say, "Thus the matter rested until Nature 

 pointed out the error, &c." Is not your language about as 

 unlike this as can well be? In response to your wish to be able 

 to tell your readers "how this sudden illumination caused the 

 scales to fall from my eyes," I hope the above explanation will 

 prove full and clear to all. 



Your second charge, " hesitancy about the matter," is a new 

 one, and so at variance with truth that necessity, even at the 

 expense of being prolix, compels me to refute it, and to show to 

 the world that this charge is as baseless as the other. How long 

 did I hesitate? I answer, from the time of the eclipse until just 

 two minutes after my arrival at home, when, though very weary 

 and ill, and before I was seated, I consulted " Webb's Celestial 

 Objects" to see how far Alcor was from Mizar. Then and only 

 then was I able to fix on a definite distance between 8 Cancri 

 and, as I then supposed, the planet Vulcan, viz., ahout 7'. I 

 left Denver the next morning after the eclipse, coming home- 

 ward, both by night and day, as fast as steam could bring me, 

 arriving at home on the P.M. of Saturday, before mo^t of the 

 astronomers had left Denver. I immediately despatched a 

 messenger to the Editor of the Rochester Sunilay Morning 

 Herald, notifying him of my arrival. I was at once interviewed 

 by him, and a full account was laid before his readers by day- 

 light the next mornbg. Sunday p.lft I was interviewed by a 

 reporter of the Rochester Democrat and Chronicle, which paper, 

 the next morning, contained a long account of my observations, 

 a considerable part of which was published in Nature. As 

 soon as possible I wrote the facts to the Astronomer- Royal, to 

 the Observatory, to Admiral Mouchez, and made out my report 

 to Prof. Colbert, of Chicago (the chief of the party to which I 

 belonged), which, with those of the other members, was pub- 

 lished in pamphlet form, also a more extended one to Admiral 

 Rodgers, not yet published. Very little hesitancy in this I think. 



I left Denver with Professors Colbert and Hough. On ihe 

 way Prof. Houvrh asked me several questions regarding the 

 distance between the two stars. I told him I was unable to give 

 their distance in arc, neither could I think of two stars whose 

 apparent distance was the same. I also said to him that the 

 nearest approach to a resemblance which I could then recall 

 were o 1 and a- Capricorni, but, not having observed them with 

 such an object in view, would not say that they were sensibly the 

 same. After they had left me — changing to another road— and 

 before my arrival at Kansas City, and before night of the day of 

 starting, the thought came suddenly to my mind that their 

 distance apart was about equal to a little more than half that 

 between Mizar and Alcor, whatever that might be, which could 

 not be ascertained until my arrival at home 



Since the eclipse I have made many observations of fl Cancri 

 and regions adjacent, to see if my judgment would allow me to 

 modify in any particular my observations as made and published. 

 I have even gone to a part of this city where the streets run 

 parallel with and at right angles to the meridian, as they did at 

 ■our camp, in Denver, and then wait until an imaginary sun some 

 30' west of 8 Cancri had the same altitude and azimuth as had 

 the real sun during totality. And, while I am not inclined to 

 make any changes what, ver, I will say that it cannot be denied 

 that, as regards the distance and direction from the sun, they 

 can only be c insidered as rough gues es. though this does not 

 militate in the least against the existence of "the new objects. 

 That they are new I know, for they are not there now. I have 

 never made a more valid observation, nor one more free from 

 doubt regarding the genuineness of the objects seen, which, in 

 my opinion, were circumsolar bodies, unquestionably int'ra- 

 Mercurial planets. The view of them was as beautiful as it was 

 unexpected, and it was with L'reat reluctance that I could break 

 away from the captivating scene. It must be borne in mind 

 that my telescope was filled with a flood of light, with not an 

 object for reference visible, and therefore, when I ran upon 

 these two round red disks, equally bright, and so near together, 

 it is not surprising that they made an impression upon my mind 

 that never will be effaced. 



The great field for future astronomical discovery will, without 

 doubt, be the sun and his immediate surroundings. Let no 

 man's prejudice deter him from taking part in such prospective 

 discoveries, for the field promises rich rewards. 



Though I have said above that I am not inclined to modify 

 my published estimations, yet I am willing to say as follows : — 

 If I were compelled to change the brightness of the two stars 

 one magnitude, and say whether they were of the fourth or sixth, 

 I should answer, the former. If I were compelled to change then- 

 distance from the sun half a degree, and say whether they were 2h" 

 or 3 J°, I should say the latter. Again, if I were compelled to change 

 their direction from the sun, and say a little farther south or north, 



1 should unhesitatingly say the latter, or, as I said in my report 

 to the Naval Observatory, south of west, instead of south-west. 

 And, finally, were I obliged to change their distance apart, and 

 declare whether they were 6' or 8', I should, without a moment's 

 hesitation, say the former, or about the distance between a 1 and 



2 Capricorni. Lewis Swift 

 Rochester, N.Y., December 10, 1S79 



The Transverse Propagation of Light 

 In Nature, vol. xxi. p. 256, appeared a paper by Mr. Tolver 

 Preston, on which I wish to make a few remarks. 



The author does not make himself very clear as to what he 

 supposes the effect of the vibrating molecules of gross matter on 

 the ether atoms to be. From what I can gather, the effect on a 

 small plane receiving the light from an illuminated "point" 

 would be of the following nature : — When the molecule of gross 

 matter was not vibrating, there would be a more or less shaded 

 spot on the plane, but if the molecule vibrated, then this shaded 

 spot would also vibrate in the same time, which would be pos- 

 sible, since during one vibration of the molecule an extremely 

 large number of ether atoms would impinge on it, and therefore, 

 a large number at each portion cf its vibration. In what fol- 

 lows I shall suppose that this is the manner in which the light 

 is supposed to be propagated. 



1. The atoms are very small ; the free paths are very long. 

 In order that the acceleration of the sun on all the planets must 

 be inversely proportional to the squares of their distances, this 

 mean path must be comparable with the radius of Neptune's 

 orbit ; and in order that the light of the stars may be visible, it 

 must be comparable with the distance of the furthest visible star. 

 Again, since, as Mr. Preston says, the automatic adjustment to 

 equality of direction is "of such a rigid character, that if the 

 atoms were imagined to be disturbed or made to move in the 

 most chaotic manner, thev would, when left to themselves, in- 

 stantly correct the irregularity," it follows that the time of 

 describing the mean free path must be very much smaller than 

 the " instantly " small time in which they "correct the irregu- 

 larity." Their velocity, therefore, must he enormous. They 

 mu.st move to the farthest visible star in a very small fraction of 

 a second. That they have a very lar^e velocity also follows 

 from the smallness of the atoms and the magnitude of gravita- 

 tion. Now the velocity of light on Mr. Preston's theory must 

 be the velocity with which the atoms move, a velocity which, 

 as has been shown, must be enormously greater than 20O,0CO 

 miles a second. 



2. The above supposes the velocity of all atoms the same, 

 which would not be true. If they varied in the same way as in 

 a gas composed of atoms which do not influence one another, 

 then at a distance from the illuminated point, after a few vibra- 

 tions of the gross molecule, the shaded spot would not vibrate, 

 but would become an elongated shaded spot without motion, 

 and there would be no light all. 



3. The data of the theory are definite, and it therefore ought 

 to be capable of explaining the laws of refraction and reflection, 

 let alone those of diffraction. This it is incapable of doing ; 

 for the light that gets through must be carried by atoms which 

 pass through without striking any of the molecules of gross 

 matter ; they mut therefore pa*s through without change of 

 direction or velocity, and therefore cannot be deflected. 



These are three reasons, each of which by itself condemns 

 the ingenious explanation offered by Mr. Preston. 



W. M. Hicks 

 St. John's College, Cambridge, January 16 



Mountain Ranges 



It is to be regretted that Mr. Trelawney W. Saunders should 

 make confusion worse confounded by noticing imaginary discre- 

 pancies based upon a mistaken assumption of a natural agree- 

 ment. In his paper " On the Mountains of the Northern and 

 Western Frontier of India," published in Nature, vol. xxi. p. 



