281, 282

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VOL. XXII.

Dr. LEE, President, in the Chair.

David Smith, Esq., Birmingham; and
John Robertson, Esq., Glasgow,

were balloted for and duly elected Fellows of the Society.

On the proposed Parallax Observations of Mars in 1862. By Prof. C. Piazzi Smyth.

In the important paper of Dr. Winnecke, of Pulkova, in the Bulletin of the St. Petersburg Academy, entitled, "Considerations concernant les Observations Méridiennes à faire pendant l'Opposition prochaine de Mars, dans le but de déterminer sa Parallaxe," that able astronomer sets forthand, as we may assume, satisfactorily-first, the large amount of uncertainty at present existing in the received value of the Solar Parallax (probablyth of the whole); secondly, the extreme desirability of improving this determination; and, thirdly, the unusually favourable opportunity which the opposition of Mars offers this autumn, beyond and before most of the recent oppositions, for attaining to the desired consummation. He then proceeds to select a series of stars admirably calculated by their position to be compared in declination with Mars, each night from August 20th to November 3d, and, finally, to announce that his method of observation will be bisection, or its equivalent, at Meridian transits with a meridian transit-circle.

Now every one knows that whatever may be done at all with a meridian transit-circle will be done by such an instrument at the Central Observatory at Pulkova, with an accuracy which will be an example to almost every country; but yet one may express surprise that in this case a meridian-circle should have been chosen; for the object proposed to be immediately gained is, a micrometrical difference only between Mars and the stars of comparison, and is therefore more suitable to a large Equatoreal, especially as the number of days during which the parallactic effect will be at its maximum is very small, and observations should rather be accumulated at that particular time than thinly spread over many months of smaller parallax.

Of course the intelligent author of the paper referred to has a reason for the opinion he has come to; and it appears to be, firstly, that in so high a northern latitude as Pulkova, measures taken with an Equatoreal "at great distances from the meridian, as recommended by Mr. Airy, would be attended with very grave inconveniences;" and, secondly, that he has not been certified that there will be any observations of any kind made at any Southern Observatory.

With regard to the first of these reasons, I cannot say anything with authority; but with regard to the second, it appears to me a duty to one of the absent Astronomers of the South referred to (viz. Sir Thomas Maclear, at the Cape of Good Hope), to mention, that I had the honour of receiving from him a letter, towards the end of 1860, detailing his observations of the Mars opposition of that year, and describing them with such extraordinary enthusiasm, and looking on them as

No. 8.

so essentially his bounden duty, that I at least entertain no reasonable doubt but that he will attend to the opposition of 1862 as honestly and as ably. Furthermore, I should mention -though without any official authority so to do, and subject to correction that Sir Thomas had made all the observations of 1860 with the 6-inch Equatoreal of the Cape Observatory, and expressed himself perfectly delighted with the superior power of that instrument for that purpose (viz. measuring micrometrical distances between Mars and certain stars near him) over the meridian instruments which he had been obliged to employ on former occasions; and he stated his belief that one night with the said Equatoreal was about as good as fifteen nights, I think, with the meridian instruments.

Hence there seems not only a chance amounting to all but certainty, that the Mars opposition of 1862 will be observed in the chief Southern Observatory, but that it will be observed with an Equatoreal in preference to a meridian instrument; and with this Equatoreal the observations will be madeaccording to the plan of 1860-not so much at great distances from the Meridian, as on and near the Meridian: a position which, it is hoped, will allow the great Pulkova telescope to be similarly employed, without any of the very grave inconveniences which had been feared for it.

Here terminates, therefore, the first part of the subject; but then immediately forces itself upon our attention this case, whether, granted that the two established Observatories of the North and South fully perform their local parts, is the desired end likely to be obtained viz. not only an accurate determination of the parallax of Mars, but a something so exceedingly accurate that it shall command the attention and elicit the respect of all other astronomers as well, besides those who have assisted at the observations, and to a degree which shall induce them to alter the parallax of the Sun as deduced from the transit of Venus in 1769?

In seeking an answer to this requirement, we are met at once by the unflattering circumstance, that oppositions of Mars have been observed again and again of late years, and without any such decided step being gained as would warrant an alteration of the received parallax of 8" 5776. What, then, can be particularly said of the opposition of 1862, that should lead us to expect much better results from it than from its predecessors? This is a point which has not escaped the acuteness of Dr. Winnecke; and he accordingly mentions-besides previous observations North and South not being very comparable -that the planet itself was not on those occasions at its least terrestrial distance, which it will be very nearly at in 1862, "or only o'4 from the Earth, the Earth's mean distance from the Sun being 1'0."

In referring to the Nautical Almanac, however, it appears that whereas the parallax of Mars will be 21"-2 on Sept. 28th, 1862, it was no less than 21"9 on July 20th, 1860; consequently the opposition of that year was more favourable in so far by, and constituted, therefore, the season when all the observations concerned should have been working for the parallactic difference, rather than in 1862. The Northern Astronomers were, however, hindered in their part of the scheme by their joining the eclipse expedition to Spain-the eclipse occurring on the 18th July, and the Mars' opposition observations extending over June, July, and August. This appears to give some excellent hints; for, if many Mars

observations were lost on that occasion, it has been allowed on the other hand by all persons, that the eclipse gained immensely by the said expedition; and, in truth, expeditions are not only most powerful means for making the most of any special astronomical phenomenon, but they have never yet had full scope given to them; although their results have been, in almost every case when they have been tried, successful. What for instance, it may be asked, would have been the transit of Venus in 1796, but for the numerous geographical expeditions that were fitted out to observe it from special and peculiar points of the earth's surface? To this question we would hardly answer, "Nothing," but rather, "A something so little accurate, that it would have yielded long since to very ordinary Mars' opposition observations."

If, then, the Venus' observations were, by astronomical expeditions, rendered so much more powerful for their useful end than they otherwise would have been, why should not the Mars observations receive the same auxiliary aid? The weaker astronomical phenomenon (for getting at the Solar parallax) surely needs all the more geographical magnifying of the effect, if its result is to be used in correcting the conclusions of the other. But if this magnifying be not done, then, no matter what result the present fixed Observatories arrive at, they will inevitably not be considered by the astronomical world to have settled the parallax of Mars; for they so plainly leave an opportunity to some one else, only a couple of years after, to make the same observations from a notoriously better baseline.

Had the observations been necessarily to be taken with a meridian circle, and necessarily to have occupied about three months, there might have been some reason for leaving the matter to fixed and established stations; but when they are more naturally to be made with an Equatoreal, as being small differences only, and might all be comprised most profitably within ten days or a fortnight, they come legitimately within the compass of astronomical expeditions; and, viewed in that light, the opposition of 1862 has this decided advantage over that of 1860, that it occurs at an equinoctial season of the year, when the light and heat circumstances of stations in high latitude both North and South will be very nearly similar.

In fact, at that season of the year and for the limited period demanded by equatoreal observations, there would seem to be no reason why an observer should not be sent to the North Cape, latitude + 71° 10', and another to the southernmost island of Cape Horn, latitude 55° 48', and thus observe with an intervening difference of 127°, in place of 94° only, the angle between Pulkova and the Cape.

There is little time left now to arrange such expeditions; but we often find, that it is precisely the shortness of time given wherein to perform any work, which calls out men's energies in accomplishing it; and, in such a point of view, there may be still quite time enough. On the understanding, too, that measures on, and near, the meridian, will be made at both stations, rather than at great hour-angles, a very portable folding dome, like Capt. Jacob's, might be easily arranged to allow of limited openings in definite directions, combined with full security to the instruments from inclement weather; and if only a week, indeed only three fine nights, could be secured about the time of maximum parallax, a remarkable micrometrical result might be obtained, and such a one as has not yet been seen in the history of Astronomy; obtained, too, not by anything so costly as what is usually called an expedition, for the whole thing would rather partake of what the French would term "une promenade astronomique."

Even this time, too, might perhaps be shortened, and the result improved, by supplementing the hand-micrometer measures, with photographic pictures of Mars and the neighbouring stars, taken in the field of the telescope at intervals

285, 286 through the night on collodion plates, and submitted to screw and microscope measurement on returning to this country.

Royal Observatory, Edinburgh, June 12, 1862.

Extract of a Letter from M. Winnecke to the Rev. R. Main, dated Pulkowa, 1862, May 30.

"I had the pleasure, a few days ago, to send you a short notice, in which a common plan of action is recommended for the observations of the approaching opposition of Mars. You, equally with myself, will be impressed with the importance of the questions at issue; and you will, I hope, at the same time, in looking through my proposals, see that they have not been made without mature consideration of the circumstances. I venture therefore to request that you will use your authority to set on foot, as far as possible, for the approaching opposition, a system of co-operation in relation to meridian observations of declination of Mars.

"I add here a few short remarks on some Variable Stars, which you will probably find an opportunity to communicate for the Monthly Notices.

"In No. 2, vol. xxii., of the Monthly Notices, which I received some weeks ago, Mr. Knott draws attention to the variable star R Vulpecula = Piazzi, xx. 457. The minimum is, according to his estimations, nearly coincident with a predicted maximum. In Pogson's Ephemeris my name is given as the authority for the time of maximum. I did certainly, star; but I was afraid that an error of transcription had crept two years ago, communicate to Mr. Pogson elements of this into them. My elements, which represent seven maxima, observed in the course of three years, with reference to Piazzi's estimations of magnitude, in August 1803, are namely

"The elements of this last star are little to be relied on, on account of the great difficulty of observing the blood-red variables. It appears, like T Cancri, to remain very long at its maximum, and to change its light slowly. For S Leonis (as the star at a = 11h 3m 363, ♪ =+ 6° 13′2, ought to be called, since a star formerly so called is still not proved to be decidedly variable), the following elements will be somewhat more

cerning the peculiar appearance of Saturn's ring, about which so much has lately been said.

Occultation: Disappearance of Jupiter's First Satellite.

1862, March 17.

h m 8

First contact

Central bisec.

7 55 4

Nice M.T.

756 39

Total immersion 7 58 43'5

Transit: Egress of Jupiter's First Satellite.

The time noted is exact; the satellite very distinct and beautifully defined; there appeared a great rupture in the southern belt near the centre, of a pyramidical shape, and a much darker colour than any other part of the belt.

Eclipse: Reappearance of Jupiter's First Satellite.

1862, March 24.

12h 13m 108 90 Nice M.T.

The satellite rather faint.

This star deserves the attention of astronomers, as, in addition to its duplicity, it has a large proper motion of +0.068 in R.A., and of +1"-68 in N.P.D.

I observed the distance and angle of position of the components of the double star on May 19, 1862; and I found for the distance (mean of six measures) 13" 51, and for the angle 283° 51'.

By comparison with Smyth's measures (Cycle, vol. ii. p. 329), it would appear that (unless he is in error) the star has been changing very rapidly both in distance and positionangle.

Observations of Jupiter's Satellites and of Saturn's Ring: Occultation of a Star by the Moon. By C. G. Talmage, Esq.

I send four observations of Jupiter's Satellites made at Nice, and three made at Mr. Coventry's Observatory, 5 Tavistock Square, and also an extract from my note-book con

29th 78 E.

Nice, February 24, 8h, 1862.

The night was not very fine, although Saturn appeared very distinct, and the peculiar marking on the ring was well defined, presenting a double serrated edge, with a distinct black line between the upper and lower edges; and the body of Saturn had, if I may use the expression, a dirty look. I only mention this, as I have not seen any observations of the kind prior to the above date, which I think shows that we are favoured with a very fine atmosphere, to see that peculiarity in our small glass.

Description of a New " Aplanatic" Eye-piece for Telescopes. By T. W. Burr, Esq.

Those astronomers who are also microscopists are probably acquainted with an eye-piece for the microscope known as "Kellner's," or the "Orthoscopic," which offers the advantage of a much larger field of view than the Huyghenian of corresponding power, and with equally good definition. It consists of a double convex crossed lens for field glass (that is, a lens having surfaces of different radii, the most convex side being towards the objective), and a meniscus of great convexity and small concavity for eye-glass. There is no stop in this arrangement.

Having experienced the benefit of this construction with the microscope, I was desirous of applying it to the telescope; and while trying the "Kellner" belonging to my microscope on the telescope of my Equatoreal, with which it produced only a low power, and when about to have another made for the purpose, I was informed that Mr. Thornthwaite (of the firm. of Horne and Thornthwaite, Newgate Street,) had improved the "Orthoscopic" microscopic eye-piece, by substituting an achromatic plano-convex lens for the meniscus. The eyeglass, in his modification, consists of a double convex crownglass lens and a plano-concave of flint-glass, forming a combination similar to one of the pairs of an achromatic microscope objective; and this construction (the field-glass remaining a crossed double convex) preserves the advantage of the large and flat field, with better definition and freedom from colour, which has induced the inventor to call it the "Aplanatic" eye-piece.

Having used this form in a microscope, I at once decided to adopt it for my telescope experiments; and therefore requested Mr. Thornthwaite to make me a suitable eye-piece, which, for the purpose of comparison, I required should be of the same power as my third Huyghenian, which, measured by Ramsden's Dynameter, gives with my object-glass a power of 123. The new eye-piece constructed for me, measured in the same way, gives 125 for its power, a sufficiently close approximation; the slight difference being against the new combination as to size of field.

I have submitted this eye-piece to a careful and lengthened trial, and can now confidently recommend it to observers, as possessing the very great advantage of a much increased field, as compared with the Huyghenian of the same power. This is at once evident on looking at the Sun or Moon, when at least one-third more of the disk of either body is visible with this eye-piece, than with the corresponding Huyghenian. For instance, with my telescope and the ordinary eye-pieces; while a power of 60 includes the whole disk of either Sun or Moon, 80 fails to do so; and with 123 on the Moon, the field includes from the South Pole to about Plato, or from the North Pole to

292, 293

the field.

The benefit of this eye-piece is also strikingly apparent in viewing clusters, such as the Pleiades, Presepe, and others; in which small stars are brought up by the increase of power and light, without losing the advantage of a large field; and in the Great Nebula of Orion, the effect is very beautiful, allowing the employment of a power which before was disadvantageous, as it made the object dim, and contracted the field; which is now large, and the nebula very brilliant. The division of double stars is rendered easier by this eye-piece, and the range of the telescope among small ones extended. For example, persons who could not see Lyræ quadrupled with the Huyghenian of 123, had no difficulty in doing so with the Aplanatic, while the detail of the planets, and generally every object, is more readily appreciated.

I send herewith sketches of the construction of the three forms of the eye-piece, viz. the Huyghenian, Kellner's, and the Aplanatic, for comparison; and also place the instruments themselves before you.*

Highbury, June 10, 1862.

293, 294

and as the state of the air was too unfavourable for observations of double stars, in which I was almost entirely occupied, I repaired to my own residence in Park Place, and turned upon the planet a very excellent 43-inch refractor of 2.7 inches aperture by Dollond, power 113.

Soon after 10h G.M.T. (time not exactly noted) the first satellite passed on to the disk of Jupiter.

At 10h 35m the second satellite was occulted. At 11h 55m the third satellite passed on to the disk. Jupiter was then without a visible satellite. At 12h 30m the first satellite passed off the disk. At 13h 30m the egress of the fourth satellite occurred. It appears, therefore, that for about an hour and twenty minutes the third satellite was the only one visible. For about thirty-five minutes Jupiter was without any visible satellite. And after the egress of the first satellite it was the only visible attendant for rather more than an hour.

The uncertainty of the times specified arises from the fact, that those which were noted at all at the instant of the occurrence, were taken from a pocket-watch, the precise error of which was unknown. And in one instance, the time was estimated from the supposed interval which had elapsed between the occurrence of the phenomenon and the procuring of a light, which was not at hand at the instant. It was this uncertainty which deterred me from presenting to the Society an account of the observation, hoping that others would be presented containing details as to time more accurately noted.

Hopefield Observatory, Haddenham, Thame, May 1862.

On the Appearance of Jupiter without a Visible Satellite, Sept. 1843. By the Rev. W. R. Dawes.

It has been lately suggested to me by the Astronomer Royal, that a remarkable phenomenon, which I happened to observe many years ago, ought to be recorded where it might be readily referred to; and that in fact there could not be a more suitable repository for it than the Royal Astronomical Society. I have much pleasure in acting upon this suggestion, being assured that no other apology can be needed for offering to the Society an observation which was made nearly nineteen years ago. I refer to the appearance of Jupiter without a visible satellite in September 1843. The observation of this rare phenomenon was immediately afterwards communicated to The Times newspaper in a letter, which principally referred to another Jovian phenomenon, namely, the dark transit of one of his satellites. I supposed at the time that the solitary appearance of Jupiter would be extensively observed; and that many communications would be made to the Society by observers possessing the means of more accurately noting the times of the different occurrences than I happened to have on that occasion. Had I been aware that not a single notice of it would be sent to the Society, I should certainly have made a communication, though in some respects imperfect, in time for the first meeting of the then ensuing session. I mention these circumstances as furnishing the only apology I can offer for having omitted to send some account of the observation to the Society immediately.

On 1843, September 27, in the early part of the evening, Jupiter appeared with all his four satellites very near him, and all approaching him. The fourth satellite passed on to the disk soon after 8h 30m G.M.T. This I observed at Mr. Bishop's observatory, with his equatoreal refractor of 7 inches aperture, by Dollond. At about 9h 50m I again directed the telescope to the planet, which very soon afterwards passed behind a tree;

* The sketches and instruments were exhibited at the Meeting of the Society.-ED.

On the Periodical Changes in the Belts and Surface of
Jupiter. By W. Huggins, Esq.

In addition to the ceaselessly varying appearances of the surface of the planet Jupiter, there would seem to be great periodic changes occurring in the conditions on the planet, of whatever nature those conditions may be, which give rise to the phenomena visible to us. It would seem therefore to be of considerable interest to bring together for careful comparison drawings of Jupiter, exhibiting in sufficient detail the more remarkable of the forms which the belts and spots assume at different epochs. For example, the comparatively inactive state of the planet during 1858 and 1859, contrasts in a very marked manner with the strongly defined and actively changing dark belts of the present year. In the hope of exciting attention to these periodical changes of Jupiter's surface, and as a humble contribution towards the commencement of such a series of representations of Jupiter, I have sent herewith a few drawings, exhibiting in considerable detail, and I believe, with great fidelity, the more characteristic of the appearances of Jupiter during the seasons of 1858, 1859, and 1860.* Objectglass 8 inches diameter, and power from 150 to 400. Upper Tulse Hill.

Transit of Titan's Shadow. By S. Gorton, Esq.

Mr. Dawes' account, in the last number of the Monthly Notices, of this interesting phenomenon on the 15th of April, concludes by stating that, in his opinion, "from the great size