Part 28 (1/2)
The haggis was adenial host with all appropriate accompaniments But the most enjoyable was the conversation of Lord cockburn, as a master of the art--quick ready, humorous, and full of wit At last, the day came to a close, and ended our way towards the city
Let , say a feords in reference to my dear departed friend David Oswald Hill His name calls up many recollections of happy hours spent in his coeniality His lively sense of humour, combined with a romantic and poetic constitution of mind, and his fine sense of the beautiful in Nature and art, together with his kindly and genial feeling, reeable friend and coenerally called, was much attached to h fireside, and was ever ready to join in our extemporised walks and jaunts, when he would overfloith his kindly syhtsns for pictures were always attractive, froement But somehohen he came to handle the brush, the result was not always satisfactory--a defect not uncohtful companion and a staunch friend, and his death h
CHAPTER 19 More about Astrono an amusement, became my chief study
It occupied e of a Reflecting Telescope of large aperture, I constructed one of twenty-inches diameter In order to avoid the personal risk and inconvenience of having to mount to the eye-piece by a ladder, I furnished the telescope tube with trunnions, like a cannon, with one of the trunnions hollow so as to adonal e to the eye The whole wasa seat opposite to the eye-piece, as will be seen in the engraving on the other side
[I telescope of 20-inch diameter mounted on a turn-table
The observer, when seated, could direct the telescope to any part of the heavens without eht, that objection was reat convenience which it afforded for the prosecution of the special class of observations in which I was engaged namely, that of the Sun, Moon, and Planets
I wrote toat St Andrews, in 1849, about this iratulated me upon my devotion to astronoht to mind many precious memories
”I recollect,” he said, ”with much pleasure the many happy hours that I spent in your father's house; and ever since I first saw you in your little workshop at Edinburgh,--then laying the foundation of your future fortunes,--I have felt a deep interest in your success, and rejoiced at your progress to wealth and reputation
”I have perused with much pleasure the account you have sent e telescopes, and I shall state to you the opinion which I have formed of it If you will look into the article 'Optics' in the Edinburgh Encyclopedia (vol xv p 643), you will find an account of what has been previously done to reduce by one-half the length of reflecting telescopes The advantage of substituting, as you propose, a convex for a plane mirror arises from two causes that a spherical surface is more easily executed than a plane one; and that the spherical aberration of the larger speculum, if it be spherical, will be diminished by the opposite aberration of the convex one This advantage, however, will disappear if the plane mirror of the old construction is accurately plane; and in your case, if the large speculum is parabolic and the small one elliptical in their curvature
”The only objection to your construction is the loss of light; first of one-fourth of the whole incident light by obstruction, and then one-half of the re 100 rays of incident light to 37 1/2 before the pencil is thrown out of the tube by a prisht, it is true, in of the large speculue speculum that is made unproductive by the eclipse of it by the convex speculuard to thethe instruenious and beautiful, and will coements which are rendered necessary for its adoption
The application of the railway turn-table is very happy, and not less so is the extraction of the ied to you for the beautiful drawing of the apparatus for grinding and polishi+ng specula, invented by Mr Lassell and constructed by yourself I shall be glad to hear of your further progress in the construction of your telescope; and I trust that I shall have the pleasure ofof the British association
In the course of the same year (1849) I sent a model of my Trunnion turn-table telescope for exhibition at a lecture at the Royal Institution, given by my old friend Edward Cowper In the ure of the observer, but the head had unfortunately been broken off during its carriage to London
Mrs Nas apparel; but Edward Corote to her, before the lecture, that he had put ”Sir Fireside Brick” all to rights in respect of his garb His letter after the lecture was quite characteristic
”The lecture,” he said, ”went off very well last night
All theso
My new equatorial was approved of by astronoun I fired was a howitzer, butplatforunner at the side of the carriage Do you know anything of the kind? Bang! Invented by one Nas at ease; the stars are brought down to you instead of your creeping up a scaffolding after the stars Well, the folks came to the table after the lecture, and 'The Nas away for a quarter of an hour, and was adht was not much insisted on, but it was said that you ran the risk of error of form in three surfaces instead of two I see that Sir J South states that Lord Rosse would increase the light of his telescope fro Herschel's plan
”De La Rue was quite delighted He said, 'Well, I congratulate you on aelse' My father, who takes very little interest in these things, said, 'Well, Edward has made me understand more about telescopes than I ever did in allery and all They were very attentive, and I never feltadministered a dose of cement to Mrs Nasmyth's friend, Sir Fireside Brick of Green Lanes, he is now in a convalescent state
The lecture is to be repeated in another fortnight With many thanks for your kind assistance, yours very sincerely,
”EDWARD COWPER”
In the course of my astronomical inquiries I had occasion to consider the causes of the sun's light I observed the remarkable phenohtness of the stars In connection with geology, there was the evidence of an arctic or glacial cliiving evidence of the existence of a condition of climate, for the explanation of which we look in vain for any at present known cause
I wrote a paper on the subject, which I sent to the Astronomical Society It was read in May 1851 In that paper I wrote as follows:
”A course of observations on the solar spots, and on the remarkable features which from time to time appear on the sun's surface, which I have examined with considerable assiduity for several years, had in the first place ledconclusion: naht, its main source appears to result from an action induced on the exterior surface of solar sphere,-- a conclusion in which I doubt not all who have attentively pursued observations on the structure of the sun's surface will agree
”Impressed with the correctness of this conclusion, I was led to consider whether we ht not reasonably consider the true source of the latent eleht to reside, not in the solar orb, but in space itself; and that the grand function and duty of the sun was to act as an agent for bringing forth into vivid existence its due portion of the illu or luciferous elehout the boundless regions of space, and which in that case , therefore, that the sun's light is the result of sos forth into visible existence the eleht, which I conceive to be latent in, and diffused throughout space, we have but to iine the existence of a very probable condition, na elelimpse of a reason why our sun may, in common with his solar brotherhood, in some portions of his vast stellar orbit, have passed, and ions of space, in which the light-yielding element may either abound or be deficient, and so cause him to beam forth with increased splendour, or fade in brilliancy, just in proportion to the richness or poverty of this supposed light-yielding eleh which our sun, in co, or is destined to pass, in following up theirelement resides in space, and that it is not equally diffused, we lihtness of stars,and more especially of those which have been known to beaain so mysteriously faded away; many instances of which abound in historical record
”Finally, in reference to such a state of change having colacial period, as is now placed beyond doubt by geological research, it appears to y to suppose that in such former periods of the earth's history our sun h portions of his stellar orbit in which the light-yielding element was deficient, and in which case his brilliancy would have suffered the while, and an arctic climate in consequence spread from the poles towards the equator, and thus leave the record of such a condition in glacial handwriting on the everlasting walls of our mountain ravines, of which there is such abundant and unquestionable evidence As before said, it is the existence of such facts as we have in stars of transitory brightness, and the above naenial climates, that renders soly hazarded the preceding reestive of a cause, in the hope that the subject may receive that attention which its deep interest entitles it to obtain