Imagini ale paginilor
PDF
ePub
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

§ 6. ON THE COLOURS OF DOUBLE STARS.

In the Cycle of Celestial Objects (vol. i. page 300-4) I have dwelt upon the colours of double stars; and in the Bedford Catalogue, which forms the second volume of that work, I have assigned such colours to all the objects as struck me at the time of observation. It seems that towards the close of the labours of Signior Benedict Sestini, of Rome, on a very extensive catalogue of stars, my book reached his hands, and led him to form the table which he has appended to his volume,* in hopes that the colours of stars may be more strictly watched. The conclusions which he had already arrived at were, that of two thousand five hundred and forty stars (those of Baily's Catalogue observed at Rome) the yellow stars are about half the total number, and equally distributed; the white stars are one-fifth, in scattered portions; and the orange rather more than one-fifth. The red and the blue are rare from the Pole to 30° of north declination; the blue then become numerous to the Equator, especially from AR. 18 to 20h; and the red abound from 0 to 30 south declination, and AR. 16h to 20h.

=

On Signior Sestini's instituting the comparisons which he has described in his work, he carefully recorded the dates, as a step to ascertaining whether the colours may or may not be found to vary with time. Political furora deadly foe to science-drove De Vico, Sestini, and other distinguished members of the Collegio Romano, from their country; and the two former sought and found an asylum in America. In passing through London, De Vico had given me notice of the use to which my Cycle had been applied; and I afterwards received a copy of Sestini's work, with the following letter in English, dated George-town College, March 19th, 1819:

* A selection from these, twenty-nine in number, was communicated by the late Professor De Vico to Schumacher at Altona, in 1849; who published the details in No. 684 of the Astronomische Nachrichten.

"Soon after I had completed this collection of observations, I conceived the design of sending a copy to you, not only as a mark of respectful esteem, but also for having profited by your Celestial Cycle in the arrangement and comparison of the observations that I myself had made in the observatory of the Roman College. But the unmerited expulsion and exile that I and my brethren have suffered, have obliged me to leave almost every thing, and the printed copies of the little Memoria remained in the printer's hands, where I think they are yet. Luckily, a while ago, I found a few copies in a trunk, sent to me after the death of our dear De Vico. Therefore I send you now what I could not send before, and at the same time and without troubling you I would desire to know what you advise upon this sort of observations. And, as I have the same objective glass of Cauchoix that I have used in Rome to collect these observations, I desire to know if you approve a review not entirely but sufficiently general in order to examine if the difference of the climate have any influence on the colour of stars. You can also, if you please, suggest more advisable means than those I have adopted, and I should be very happy if the opportunity of having the same and so good an objective glass that I have used for ten years in Italy could give me the means of lending some advantage to the science: what so sincere a lover of this beautiful science as you are can easily find. On another occasion, and when I become better acquainted with the English language, I hope to thank you for all your favours and kindness. Then also I will tell something of the new observatory of this George-town College, erected and very well furnished by the care of M. Curley, a very able and industrious professor, my colleague.

"The observations made and published with my first Memoria are reprinted and collected together with all the others of this second Memoria. Nevertheless, if I had here a copy, I would join to the second, and I would send both to you.”

In reply to Signior Sestini, I expressed my satisfaction with the course of his inquiries, as they might yet be of great value in a very interesting branch of physical phenomena. He should, however, remember that the colours I had recorded were frequently noted after the eye was fatigued and biassed by previous working in an illuminated field, and reading minute divisions on graduated micrometer-circles. There were also the imperfections of the eye, the materials of the object-glass, and the various atmospheric media to be considered, before any crucial exactness could be expected; but that still, under every objection, approaches to satisfactory conclusions must inevitably follow a stricter attention to the subject. I therefore recommended occasional references to the heavens for this object only, with the eye kept in sharp order for the purpose, having carefully experimented the capacity of that organ in strictly identifying the many gradations of colour. Many of the tints of stellar companions would of course turn out to be merely complementary

contrasts; but the inherent colours would become additionally valuable, as strict observation upon them, under efficient means, advanced.

The question is pregnant with interest; and, as I consider it may be advantageously encountered by any sharp-sighted amateur who, possessed of a good telescope and inclined only to easy and pleasing work, is nevertheless desirous of being useful in the cause of knowledge, I have therefore subjoined the list of chromatic comparisons of Sestini's observations with mine; to which I have added those colours which I have since noted at Hartwell. Several of these were confirmed in direct comparison by Dr. Lee; it was an occasion on which the eyes of ladies were prized, and the tints were mostly pronounced without reference to the older records.

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]
« ÎnapoiContinuă »