Astronomical Register: A Medium of Communication for Amateur Observers and ...

lost in that awful abyss which separates us from the stars, and without making any sensible approach even to the nearest of them in many hundreds or thousands of years. The power by which the sun is enabled to perform this office-to gather planets round its hearth and to keep them there is the same in kind (though very different in intensity) with that which, when a stone is thrown up into the air, draws it down again to the earth.-Orb.

THE WEATHER.-A new weather-book, entitled A Manual of Weathercasts and Storm Prognostics of Land and Sea, or the Signs whereby to Judge of Coming Weather, has just been published by Routledge & Sons. The author is a Mr. Andrew Steinmetz. The very moderate price will, no doubt, obtain for this work a large circulation.

HAIL AND RAIN.-An interesting essay on the cause of hail and rain has been laid before the French Academy by M. Renou. Rain and hail, according to the writer, are produced in the same way-viz., by the passage of a snow-cloud, or cirrus, through a vapour-cloud, or cumulus. The cirrus is generally situate at a height of nearly 7,000 yards above the earth, and consists of fine particles of congealed vapour. Under certain conditions it falls through the cumulus, which is generally at a much lower level, and in doing so it adds to the water the latter contains, and by abstracting its heat converts it into rain. If the abstraction of heat goes on to any great extent, the particles of water become frozen, and fall on the earth as hail.

THE OPALESCENCE OF THE ATMOSPHERE.-At the Royal Institution, on June 1, Professor Roscoe, of Manchester, lectured "On the Opalescence of the Atmosphere." The term opalescence in respect to the atmosphere requires, perhaps, a little explanation, although it may be sufficiently suggestive, to those who are intimately acquainted with the phenomena of light, of what it is meant to indicate. What, for example, is the cause of the blue colour of the sky, has long been a subject of consideration. Many, like Leonardo di Vinci, have regarded it as a mixture of white light with the outer blackness of space, or rather, as a mere veiling of the intense darkness of space by the gradually dispersing sunshine-a view supported by Goethe. Newton conceived it to be due to the presence in the air of myriads of minute hollow vesicles of water, which, through certain phenomena of interference, allowed only the blue rays to be transmitted, whilst they reflected the red rays, as seen at the times of sunrise and sunset. Other physicists have regarded these atmospheric effects as ocular deceptions; whilst Forbes and others have considered them as due to the presence in the air of minute globules of water, or very fine particles of solid matter. But whatever the cause-and the cause as yet has not been decisively ascertained-it is necessary to have a term that shall be generally expressive of this class of phenomena. If we look at the sun through steam it appears as a red ball, the same as it looks through a London fog. If we look at the sun through a piece of opal glass, such as is commonly used for the shades of gas-lights, the sun will present the same red appearance, while the light reflected from the opal glass will always possess more or less of a bluish tinge. The like effects are exhibited by natural opal, and in all cases are due to the presence in a transparent medium of very minute particles of foreign substances having a different effect on the rays of light to the medium itself. The word, as used by Professor Roscoe, is an apt and expressive one for this class of meteorological phenomena. But in this opalescence or natural mistiness of the atmosphere other important phenomena are involved, which Professor Roscoe, in connection with Professor Bunsen, of Heidelberg, and Mr. Baxendell, have been for some years

past engaged in investigating. One of these considerations has been the variations in the intensity of the chemical action of light at different hours of the day, seasons of the year, and states of the atmosphere. And the two main points dwelt upon in the present lecture were the greater proportionate intensity of chemical action in diffused daylight over that in direct sunlight, and a comparison of the observations made at Para, a town on one of the southern mouths of the Amazons, one and a half degree south of the equator, with those made at Manchester, Kew, and Heidelberg. It has often been asserted that photographers experienced great difficulty, and often an impossibility of taking pictures in tropical regions, and this has been attributed to a want of actinic power in the solar rays. The observations now recorded seem to prove that it has been a superabundance of chemical action rather than a want of it, the relative proportions in one case of instances selected for comparison being 260 for Para against 19°7 for Kew, and thus it is probable that photographers have commonly exposed their plates at least seven times and often fifty times too long to the action of tropical light. The lecturer illustrated the general conditions and effects of opalescence by numerous experiments, some performed with the aid of the electric light. The audience were lit out of the lecture-hall by Mr. Larkin's magnesium lamp-the first time, we believe, t has been publicly exhibited. The magnesium is not burnt in it as wire, but falls in the state of fine powder upon a small gas jet, by which it is inflamed, and a bright continuous light is kept up. We have known for some months of Mr. Larkin's endeavour in this direction, but we kept silence, hoping he would succeed in overcoming the slight amount of flickering which is the only bar to the perfection of this method. The change in the aspect of the bright colours of the ladies' dresses was very great, every tint coming out with singular freshness.

CHAMBERS'S ASTRONOMY.-We understand that a new edition of this work, greatly enlarged, and with many additional illustrations, is in the press. It will appear under the auspices of the University of Oxford, as one of the Clarendon Press series of Scientific Manuals.

BREGUET, THE FRENCH WATCHMAKER. This celebrated man was greatly encouraged by the Allies in 1815. The Emperor Alexander purchased several of his unequalled watches, and the Duke of Wellington also had one which, on touching a spring at any time, struck the hour and the minute. The Duke carried it for many years, and it proved of great service to him on many occasions. It cost, I was told, three hundred guineas. Breguet was, without doubt, the best and most scientific watchmaker known. I frequently visited his shop, and had many conversations with him; and although at that time getting old, he was full of energy and vivacity. He was not an advocate for flat watches, as he said they impeded the proper action of the wheels, and could not be depended upon as timekeepers. He defied any one to make a watch so good as those made on his own principle. The prices he paid to his best workmen were enormous, there being few to whom he could confide his watches, as so many were drunkards, and could only work a day or two in the week. He told me that he paid some of them thirty francs a day, and none less than a Napoleon; and that throughout Paris there were only fifteen or twenty able to execute the delicate work necessary for such watches as he made. Breguet was a great encourager of merit. He used to say to his young workmen, "Don't be discouraged, or allow a failure to dishearten you; accidents will happen; miscalculations cannot altogether be avoided; be persevering, industrious, sober, and honest." Such was the advice he gave,

and he frequently enabled those in his employ who were skilful, steady, and industrious, to arrive at opulence. Breguet, besides his scientific knowledge and mechanical skill, possessed great general information. Napoleon himself, knowing his abilities, frequently went incognito to the workshop, and conversed upon the improvements which he was anxious to effect in cannon and firearms. The Russian campaign and its disasters put an end to all projects on that score.-Captain Gronow's Past Recollections, p. 108.

COLOUR OF THE STARS.-If the stars be observed on a clear night, it will be seen that they shine with different colours. The most noticeable hues are red, white, and yellow; no stars exhibit a distinct blue or green colour, though some have a bluish or greenish tinge. In our northern latitudes, where the air is scarcely ever free from haze and vapour, this diversity of colouring is not, perhaps, very striking; but in southern climes, and especially in inland regions, where the air is less humid, the effect is far greater the whole vault of heaven seems set with sparkling gems. The difference of tint we have mentioned is perceptible to the naked eye, in our clime, only among stars of the first and second magnitudes. Even among these, observers differ slightly... . . . The ancients noted some of these brighter stars, and we thus learn the remarkable fact that their colours are not unchangeable. Sirius was celebrated in the writings of the ancients as a bright red star; it is now decidedly white. Other changes have been noted, and some of these have occurred within a comparatively short time.

Among the stars either altogether unseen, or but faintly visible to the naked eye, the telescope reveals the same diversity of colouring. Many of these stars, indeed, are found to be coloured in a more marked manner than those we have hitherto mentioned. Stars are found shining with a scarlet, blood-red, brilliant orange, or deep yellow colour. Still, however, no stars of a deep blue or green tint occur singly. Thus far, then, the telescope has merely extended the range of our view, without disclosing appearances differing in any important respect from those already observed. When, however, a telescope of sufficient power is directed successively to double or multiple stars, we soon notice a new and singular phenomena. Not only do we find every shade and tint of the primary and secondary colours, and such hues as grey, fawn, and ash-colour, but we notice that in many cases the stars forming a binary system are of complementary colours. Struve has observed that this is the case in upwards of one hundred of the double systems. In triple and multiple systems, similar arrangements of colour are noticed.

THE MOON UNDER ECLIPSE.-Secchi, in the Bulletino Meteorologico, asserts that the bluish-green light which fringes the red moon in a lunar eclipse is merely an effect of contrast. The assertion is founded on observations made with a very small field of view.

LUMINOSITY OF THE SUN.-Secchi, writing under the date of April 24, 1866, says: "I have just completed some investigations as to the comparative luminosity of the central and marginal portions of the solar surface: I find that a great difference exists. Taking the centre at 1, the margin is only 3rd or 4th. The boundaries are rather indeterminate, for I have been impeded a little by an unforeseen embarrassment; the light near the edge is ruddy. Indeed its colour possesses a very marked rose tinge, and this renders photometric measures very difficult."—A.N. 1585.

THE GREENWICH OBSERVATORY.-- Some interesting papers on this observatory have lately appeared in the Gentleman's Magazine, from the pen of Mr. J. Carpenter.

THE COMPANION OF SIRIUS.-Admiral Davis and Mr. Newcombe, of Washington, have communicated to the A. N. (1584) some measures and notes on the above object regarded as the disturbing body whose existence is indicated by theory. Mr. Newcombe says:-" A comparison of the above [measures] with previous measures does, I conceive, show decisively that the observed companion is really the body which produces the known irregularities in the proper motion of Sirius." The argument for identity may be summed up thus:--(1.) The motions of Sirius indicate that it has a companion which in 18640 was about in the direction 82°, and was moving around it at the rate of 18° per year. (2.) We actually see that Sirius has a companion which in 18640 was in the position 80°, and is revolving at the rate of 2.3° per year." The identity may therefore fairly be considered as established.

THE TELESCOPE.-The Rev. C. Pritchard, the president of the Astronomical Society, delivered a lecture "On the Telescope," at the Royal Institution on May 18. The subject was evidently one beyond the limits of an hour's discourse, as viewed in its historical aspect; and hence, while the earlier phases of improvements in lenses had a full share of notice as the passage of time proceeded, the more interesting points in the exquisite condition of the modern instrument had unfortunately to be too much curtailed. The first convex magnifying glass or lens actually seen was one found in an engraver's shop in the ruins of Herculaneum. The next advance in the application of lens seems to have been in the thirteenth century for spectacles. Early in the seventeenth century a spectacle maker observed that distant objects seen through the spectacles hanging in his window were inverted, but seemingly to the vision brought nearer. He did not apply practically his observation, and his name has been lost to fame. In a record of the States General of the Netherlands, preserved at Hague, one Hans Lippersley, a spectacle maker at Middleburg, in 1608, petitions the Government in respect to a telescope he had constructed of two spectacle lenses, and the authorities ordered three at 75%., but on the condition that they should be seen through with both eyes. From this time a few such instruments were made occasionally for the amusement of the rich or great, who used them in looking at church vanes and passing objects until in the following year the knowledge of them came to Galileo. After him their construction was advanced by Huyghens, in 1656, and thence no great improvement was effected up to the time of our own Dollond, in 1758 and following years. The principles of the defraction and diffusion of light, and the differences in the focal lengths of rays bent through the extremities of lens from those passing through the centre, and various other phenomena of lenses with the remedies for defects, were illustrated by model, and exhibitions by the electric light. In conclusion, the lecturer, after expressing his admiration of the perfection of our modern English instruments as now produced through the conscientious skill of Cooke, Dalmeyer, and Simms, wound up with a few pithy and wellturned observations on the opportunities afforded by the telescope for doing honour to the Creator of the universe, as the highest aim of the astronomer.

[The above is from a correspondent. We are, however, glad to announce that Mr. Pritchard has prepared an abstract of this Lecture specially for us, which will appear during the recess.—Ed.]

Greenwich ObseERVATORY.—The annual visitation was held on Saturday, June 2. The weather was very fine, and a large assemblage was the con

sequence.