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influencing the development of colour. The observations which constitute Appendix I. are so important that I have read it over repeatedly. It seems to me that the variations of colour and intensity should also be sought for elsewhere than in the double stars. I have ascertained that at three epochs (at least) 8 Urs. Min. has become redder than usual. Observe that in the presence of artificial lights, which are always reddish, red stars appear white: thus, when 3 Urs. Min. seems very red (even more so than Arcturus), there is no fear of having mistaken its tint. And Sirius, which, away from towns, exhibits a pure white, when seen from Paris looks blue, like moonlight reflected by water in the streets. Lalande persisted in calling Sirius blue. During twilight the stars assume tints according to the colour of the sky, and then it is that we can perceive the influence of the intensity of light on the tint of a star according to the predominant colour of the region where the star is placed. Thus the orange tint of Venus in an evening blue sky was remarked by Ovid. Lalande erroneously styles her yellowish. But 8 Urs. Min. is the only star that I have found variable.

Everybody approves of your graduated scale of tints; and M. Chevreul thinks that with coloured glasses we might have a collection of your twenty-four tints, which might be easily and profitably consulted to fix undeniably the tints of sidereal chromatics.

Another sidereal quality I have observed with great interest is, that some stars have more power of overcoming twilight than others of the same mag. for instance, compare a Cygni (Deneb), almost a 1st mag., the brightest star in our latitude, and possessing scarcely any parallax, with y, d, or e, of 3rd mag. We perceive y as soon as a, whilst d and & are perceptible only later; yet when quite dark y is not brighter thand or ε. This fact was published some years ago. Now as to the cause-Let us suppose a star just sufficiently bright to be perceived in twilight; its light then must be equal to at least th of the uniform light of the sky. But if we imagine that this star, preserving the same brightness, is smaller, and thereby occupies only 4th of the space it did before, then its light will beth of the general light of the sky, and will consequently be very perceptible. One of the stars of Cassiopeia possesses this power of conquering twilight; so does y Draconis, Pegasi, and others. It is easy to prove this by an optical experiment. I cannot sufficiently thank you for your letter, and remain, &c. BABINET, DE L'INSTITUT. Paris: March 2, 1865.

OBSERVATIONS OF FIREBALLS.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-The recent observations of a detonating fireball in Scotland, in the month of February last, correspond very nearly to one of the dates named in the pages of the Astronomical Register among the list of "Dates preferred by fireballs" (see diagram to p. 10, No. 25). The dates there stated to be preferred in February are the 2nd, 10th, and 19th days of the month, and this meteor took place upon the 21st.

The occurrence of this large fireball serves more especially to establish the meteoric character of the last of these three dates, or the 19th of February. I am not aware that any other fireball was observed in February. It is important to note particularly the position in the heavens occupied by a fireball at any time and place, as it is from a comparison of these observations with others of a similar nature made elsewhere that the distance of the meteor from the earth, and its rate of motion, can be calculated, as well as the part of space from which meteors of the larger kind are directed at any particular season of the year. I am, Sir, yours obediently,

Collingwood, Hawkhurst:
March 7, 1865.

ALEXANDER S. HERSCHEL.

The following observations refer to the meteor here alluded to by Mr. Herschel :

:

On the 21st of February, 1865, at 9h. 12m. P.M., an exceedingly large meteor appeared at Arbroath, Forfarshire, N.B. The glare of light upon the landscape resembled that of noonday, and was of a yellowish colour. The meteor resembled the full moon in size and colour, but was followed by a tail of green and yellow light, having a rapid undulating motion. It shot rapidly from Aldebaran (a Tauri) to Betelgeuse (the star a), on the right shoulder of Orion. The duration was only a few seconds, and it disappeared without noise. The same meteor was observed also at Innerleithen and at Walkerburn.— Scotsman.

At Pratis, in Fifeshire, N. B., the sky was clear from a quarter after nine to half-past nine o'clock P.M. on the evening of the 21st, when this meteor appeared, and the light of the meteor reflected from the snow was of the most vivid description. The meteor was to appearance as large as the full moon, white, and pear-shaped, tapering at twice or three times its breadth to a point of red sparks. It shot across the sky from the north in a south-westerly direction. minute after it had disappeared a long rumbling noise was heard, which continued two minutes, and was by many persons mistaken for thunder. The sound gradually increased in intensity, and then lessened and died away.-Fife Herald.

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P.S.-The meteoric character of one of the October dates in the above-mentioned list (the 13th-14th October) is supported by a passage which occurs at p. 194, vol. ii. of Captain C. F. Hall's new journal of Arctic voyages, entitled Life with the Esquimaux (Sampson Low: London, 1864, 2 vols. 8vo.). The passage is the following:In the volume where it occurs it is accompanied by a plate representing an auroral display, with streamers traversed by a fireball. companying illustration represents a still more remarkable display (of the aurora) which occurred on the evening of October 13, 1860. One feature connected with this was a meteor of great brilliancy, which shot from a point in the heavens near Cassiopeia, crossing Ursa Minor, and losing itself among the folds of Draco. It was followed by a trail of light twenty degrees in length." A. S. H.

TRANSIT OBSERVATIONS.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-As there may be many of your readers who are endeavouring to acquire the habit of making good transit observations, but who, like myself, have not the advantage of a skilful friend to instruct them, and are therefore obliged to rely entirely upon directions as given in books, I much wish to take this opportunity of giving a caution, which I have not observed in the best works on the subject. When I first began taking transits, two or three years ago, I often experienced a difficulty which annoyed me much. When the eyepiece was adjusted, so that vision of the wires was beautifully distinct, I found that just as a star approached a wire, the wire would frequently suddenly become indistinct, as if out of focus, and sometimes appear double-thus, of course, vitiating the accuracy of the observation. I was a good deal puzzled, and began to fear that I laboured under some defective vision, when, one night, it occurred to me that I would try the effect of reducing the illumination considerably; and I was quite pleased with the result. I found that the wires were better defined, and, as a consequence, the observations were improved, as evidenced by the closer agreement among themselves of the intervals of time from wire to wire, and the closer agreement of the clock-errors deduced from the transits of four or five Nautical Almanac stars-the times of the transits being, of course, corrected in the usual manner for the instrumental errors. I may here add that I not unfrequently take a set of transits of four or five Nautical Almanac stars, of which the highest and lowest may differ 50 or 60 degrees in declination; and find that the greatest and least clock-errors of the series may not differ more than three or four tenths of a second, while the clock-errors of the highest and lowest star may not differ more than two-tenths of a second. Proficients do much better than this; but I presume such results, though not satisfactory to the writer, are pretty fair for an amateur who has had no instruction whatever from a practised observer. The following works have been most carefully studied:-The article "Transit" in the Penny Cyclopædia, by the late Rev. R. Sheepshanks - a well-known standard treatise; Loomis's Practical Astronomy, which also treats of the transit instrument very fully; Simms's Mathematical Instruments, and the Prolegomena of the Celestial Cycle; which contain, as might be expected from such a source, many most valuable suggestions on the use of the Transit: but in none of these do I remember any caution about the illumination, which has proved a great stumbling block to myself. It would be interesting to learn whether any of your readers have met with the same difficulty.

The transit instrument used is a very excellent portable one, by Troughton and Simms, of 30 in. focal length, and 24 in. aperture, almost exactly similar to the one so well delineated in Mr. Sheepshanks's article above mentioned.

I am, Sir, yours obediently. HUNT.

Chad Road, Edgbaston, Birmingham:

Feb. 13, 1865.

THE PENDULUM EXPERIMENT.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-Referring to a letter in a recent number of the Register, signed "F. G. S.," as also to remarks made by one or two other corre spondents, it appears that considerable doubt exists as to whether the pendulum experiment really does produce certain and visible evidence of the earth's axial rotation.

Now, as it is currently admitted in our astronomical literature that it does so (vide Arago, Sir John Herschel's Outlines, 6th edition, Orr's Circle of the Sciences, &c.), the subject seems to me to require a little further " ventilation," by way of verifying, if a fact, or exploding, if a fallacy.

As the "Moon Controversy" is now so nearly concluded, would not this be a fitting subject to occupy a few pages in the Register? After the doubts that have been alluded to, it surely cannot be satisfactory to your readers, nor to the scientific world generally, for a matter of so much interest to remain in a state of uncertainty. Perhaps M. Léon Foucault himself will come forward to the rescue, confirming his own discovery; but doubtless several of your subscribers are equally competent, if the matter is capable of being established on a sure basis.

Garstang.

I am, respectfully,

Č. W.

CLOSE DOUBLE STARS.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-In answer to your correspondent, Mr. W. Matthews, I beg to state that the following recent measures of n (eta) Orionis, made by Mr. Knott, are given by the Rev. T. W. Webb in the Intellectual Observer, No. 38, p. 140.

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The measurements of the following stars are extracted from Bishop's Catalogue of Double Stars, 1839-50.

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7 Tauri, A & B

1841 957

263'47 0.6 est

The distances given above for Cancri A & B and A & C are respectively for the epochs 1843 266, and 1843 285-the distances not being given for the last epochs at which the angles of position were measured. 52 Arietis I do not find in Bishop's Catalogue. I am, Sir, yours faithfully,

Colchester: March 8, 1865.

G. J. JONES.

THE TRAPEZIUM AND . IN ORION.

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TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir, I trust that I may be permitted to express my thanks to your correspondents for their valuable and obliging notices of my letter of Jan. 12, and to add that, on a serene evening, that of the 26th ult., the 5th and 6th stars in the Trapezium were both distinctly and steadily visible in my 44-in. refractor.

I should be glad if any of your correspondents would do me the favour to say whether, between the two quadruple stars in 48 Orionis more than two small stars are visible, and in what position, and with what aperture. Mr. Darby states, in his Handbook, that Struve, with the Dorpat Refractor, reckoned 15 stars in the group. The two small stars making, with the double quadruple, ten, are very easily seen in my instrument, but I have not yet seen any others.

I am, Sir, your obedient servant,
D. A. FREEMAN.

Menton (Alpes Maritimes):
March 11, 1865.

THE PECULIARITIES OF VISION OF ASTRONOMICAL OBSERVERS.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER. Sir,-The enquiry of Mr. D. A. Freeman has led to the publication of much interesting and instructive information to students of astronomy. There is one fact which the letters of your correspondents strikingly exhibit, and that is, the great difference that occurs in the observations of different observers using instruments of about the same size and capability.

Thus, while Mr. Wray sees the 5th star with 3 aperture, C. W. has gazed long and earnestly at the same object with 44, and can only see the four principal stars, yet he constantly sees the companion of Aldebaran, 12 mag.; and I am unable to distinctly see Polaris with a good 2-inch aperture of fine definition, though Mr. Dawes sees it with 1, and considers 2-inch should hold it steadily. As to Rigel, I have often carefully studied this star, but could never see the companion, though marked 9 mag. ; yet I can constantly see the companion of Aquarius of the same magnitude, and can see many other stars of 95 mag. Possibly the colours of different stars may have an influence on their visibility. Neither is this peculiarity confined to beginners in astronomy, for it is stated in Mr. Webb's Celestial Objects that Herschel II cannot see the coarse mottling (not willow leaves) of the sun's surface with any achromatic, while Mr. Dawes states that a good 2-inch object-glass and power 30 or 40 will well show it; and I can almost constantly see it with this aperture and a power of 50 or 60.

I

And respecting the observations of De Vico on Venus, 1839-41, find it stated-" Of six observers the most successful in seeing these faint clouds (spots on Venus) were those who had most difficulty in catching very minute companions of large stars;" and in a foot-note

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