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It fell to me to tell my lord what had passed. He heard me out, and then went up to the picture of his son which hung beside his own, and stood gazing at it while a man might tell his beads over.

• Take it away,' he said at last—and we did so. I scarcely dared tell him the message I was charged with, that Messer Guido had asked to see him once before he went on pilgrimage to the Holy Sepulchre. He heard me speak, and then before he answered his eyes blazed so, that I shrank from him, old man as he was, and unarmed, but he spoke quietly.

'He has been a curse to the city ; he has killed the sweetest lady that ever walked this earth; he has brought ruin on our house, and dishonour on a name that was stainless till the judgment of Heaven granted me the son I prayed for. Tell him all that-and if he asks for other answer tell him plainly I will never look upon his face again.'

He never did—I think perhaps even now he would refuse to do it, though he is breaking his heart for the memory of what has been, and I can see it will not be long before we lay him with the rest of his race in the church across the square.

And now, some may say it was but a little thing for which my master lost his life (for even if he lives still it can be but a living death).

To such I can only answer, 'Was it not for a little thing that Adam lost Paradise?' Moreover, what he did was done with open eyes and of set purpose. And yet, though none shall ever hear me murmur that his life should be spent in hopeless wandering till his dying day, yet I cannot but think of him as he once was, and for the love of my master, as I knew him long ago, I would pray all those who read what I have here set down that they say but one prayer for him, alive or dead. And though I may not live to hear it, I trust that he shall yet find mercy, for the sake of One who suffered in a garden to redeem those who sinned in Eden.

C. M. WHIDBORNE.

CELESTIAL PHOTOGRAPHY.

BY J. E. GORE, F.R.A.S.

The first idea of photographing the heavenly bodies may be dated back to the great discovery made by Daguerre and Niepce, and communicated by Arago to the French Academy on August 19, 1839. Daguerre attempted to photograph the Moon in 1840, but apparently without much success, and to Professor J. Draper seems due the credit of obtaining, in the same year, the first lunar photograph. He was also the first to photograph the solar spectrum. This was accomplished in 1843. The earlier photographs were called daguerreotypes, after the inventor, and a series of plates of an eclipse of the Sun, now almost obliterated by time, are preserved in the museum of the Paris Observatory. These plates have no date, but they are probably photographs of the total eclipse of July 8, 1842-an eclipse which was also photographed by Majochhi, at Milan.

In April, 1845, Messrs. Fizeau and Foucault obtained a good photograph of the Sun with an exposure of 'th of a second, which showed some sun spots, and also gave some indications of the fact, now well known, that the centre of the solar disc is brighter than the portions near the limb.

The solar eclipse of July 28, 1851, was photographed by Berkowski at Kønigsberg, and upon this plate are seen for the first time traces of the solar corona and red flames.

In 1853 and 1854 Mr. Hartnup, at Liverpool, and others, obtained good photographs of the Moon, and the solar eclipse of May 26, 1854, was photographed by Professor Bartlett at Westpoint (U.S.A.).

In 1856 the late Mr. De la Rue established an observatory at Crauford, having a reflecting telescope made by himself of thirteen inches aperture and ten feet focal length. In the following year he obtained with this instrument good photographs of the Moon, Jupiter, and Saturn. It may be mentioned here that by photographing the Moon at suitable intervals, and taking advantage of the small changes caused by libration, it is possible to obtain pictures which, when viewed in a stereoscope, give the appearance presented by a spherical body.

In 1859 Mr. De la Rue constructed a large photo-heliograph at Kew, and with this instrument over 2,000 photographs of the Sun's surface were obtained in the years 1862 to 1872. In the years 1850 to 1871 six eclipses of the Sun were photographed with varying success, but most of them showed details of the corona and protuberances. Photography was also applied to the observation of the transits of Venus in 1874 and 1882, but the results obtained in this way were of doubtful value.

The first attempt to photograph the stars seems to have been made in 1850 by W. C. Bond and Whipple, with the equatorial telescope of the Harvard Observatory (U.S.A.). They succeeded in obtaining images of the bright star Vega and the double star Castor, but the daguerreotype plates used were not sufficiently sensitive for such delicate work. A very long exposure was necessary for even a bright star, and the impossibility of obtaining impressions of the fainter stars led them to abandon their efforts. On the introduction of the collodion process, however, in 1857, Bond again attempted to photograph the brighter stars, and succeeded in obtaining images of stars of the first and second magnitude with an exposure of only two seconds. He also photographed the double star Mizar (Zeta Ursæ Majoris), and from measures of the photographed images he obtained a very accurate result for the position, angle, and distance between the components of this well-known pair, a result which agreed closely with Struve's measures made directly with the micrometer.

In the year 1864 Dr. Rutherfurd, of New York, constructed an object glass of eleven inches aperture for the photography of the stars which gave better results than a mirror of over twenty-three inches in diameter. With this instrument he obtained good photographs of the Præsepe and the Pleiades, which showed stars down to the ninth magnitude. Following Rutherfurd's methods, Dr. Gould, in the years 1870 to 1882, photographed the principal star clusters in the Southern Hemisphere at the Cordoba Observatory in the Argentine Republic, and obtained plates showing stars to the tenth and eleventh magnitudes, some of them containing 500 stars to the square degree.

We now arrive at an epoch when the photography of celestial bodies was much facilitated by the introduction of the dry plate process. The old wet plate process with collodion required enormously long exposures, and was difficult to manipulate. The discovery of the gelatino-bromide of silver process, however, allowed much more sensitive plates to be used, thus reducing the time of exposure necessary for faint stars, and permitting more work to be done in a given time. The advantage of a short exposure in a climate like that of England is obvious, for with a long exposure the sky may cloud over before the photograph is finished. The introduction of the dry plate process gave a fresh impetus to celestial photography. In the year 1881 Professor Draper obtained a good photograph of the great nebula in Orion with an exposure of one hour, and a still better photograph of this wonderful object was obtained by Dr. Common in January, 1883

About this time Professor Pickering, at the Harvard Observatory, commenced to take a series of plates showing all stars to the naked eye, and this work is now far advanced towards completion.

The idea of forming a complete chart of the whole sky by means of photography seems to have been originally suggested by Mr. De la Rue about the year 1857, but the possibility of carrying out the idea does not seem to have been recognised until Dr. Gill, in 1882, obtained a photograph of the comet of that year with an exposure of 1 hour 50 minutes. On this photograph numerous faint stars are sharply shown, and Dr. Gill's success proved that a photographic chart of the sky was now possible. The same suggestion seems to have been also made by Dr. Common in the same year.

In the year 1884 Messrs. Paul and Prosper Henry, of the Paris Observatory, while attempting to complete by eye observations at the telescope the ecliptic charts left unfinished by Chacornac at his death in 1873, came across regions of the Milky Way so rich in the fainter stars, which it was necessary to show on these charts, that they found it impossible to record them in their correct places. The idea then occurred to them that the work might be successfully accomplished by the aid of photography. To carry out this plan they constructed a special photographic equatorial telescope with an object glass of thirteen inches aperture, and with lenses corrected for photographic work. To this instrument is attached a second telescope of about nine and a half inches aperture, which serves as a finder in following the stars to be photographed, and corrects any error in the rate of the clock which drives the whole apparatus. Complete success crowned the efforts of these admirable astronomers, and the excellence of the stellar photographs obtained can only be appreciated by those who have seen the originals. The present writer has in his possession a number of paper prints from the original negatives, very kindly sent to him by the brothers Henry. On these the stars are shown as perfectly round white discs on a black background, and their extreme beauty can hardly be adequately described.

The duration of exposure necessary for obtaining images of stars of different magnitudes varies, of course, with the brightness. At the Paris Observatory it has been found that, with the extra sensitive plates now used for the purpose, stars of the first magnitude can be photographed with an exposure of both of a second, and stars of the second magnitude in about both of a second. Stars of the sixth magnitude-about the faintest visible to ordinary eyesight without optical aid-take about half a second ; those of the ninth magnitude about eight seconds; those of the twelfth about two minutes ; and for stars of the sixteenth magnitude about the faintest visible in the largest telescopesan exposure of 1 hour 20 minutes is required.

The long exposures necessary to obtain images of the fainter stars cause those of the brighter stars to be much ‘over exposed,' and these latter appear on the photographs as discs of considerable size. There is, however, a relation between the size of the disc and the brightness of the star, and estimations of relative brightness can be obtained by measuring the diameter of the discs with an instrument which has been invented for the purpose. Stars of a red colour are, of course; more difficult to photograph, and the images of these ruddy stars come out with much smaller discs than those of white stars of equal brilliancy to the eye.

The superiority of the photographic method of stellar mapping over eye observations will be understood from the fact that a chart of the Pleiades constructed by M. Wolf with a large telescope shows 671 stars in this well-known cluster, while on a photograph taken at the Paris Observatory with an exposure of three hours over 2,000 stars can be counted! Indeed faint stars are visible on these stellar photographs which cannot be seen by the eye (in) the telescope with which the photographs were taken. In fact, the success attained at the Paris Observatory in stellar

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