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XXIX.—The Visual, Grating and Glass-lens, Solar Spectrum (in 1884)

Published online by Cambridge University Press:  06 July 2012

C. Piazzi Smyth
C. Piazzi Smyth
Affiliation:
Astronomer-Royal for Scotland.
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Extract

Throughout the year 1884 the sun was seen over most countries under peculiar atmospheric circumstances; and these, instead of being confined to low altitudes, were never more conspicuous than during the summer of the year, and noon-tide of each day, and in the clear air on mountain heights of every country, whenever the sky was more or less free of actual clouds.

On such occasions then, the usual phenomenon to be noticed by the eye, was, that nothing like blue sky could be witnessed near the sun. But in place of that, there was a broad glare of whitish light extending for several degrees around the luminary; and beyond that range, or over 20 degrees distant from him, there spread a wide reddish haze, passing into purple, and at greater distances into blue, but nowhere a very decided and deep blue sky.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 32 , Issue 3 , February 1886 , pp. 519 - 543
Copyright
Copyright © Royal Society of Edinburgh 1886

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References

page 524 note * From observations taken by my friend, Mr Rand Capron, F.R.A.S., at Guildoun, Guildford, Surrey,—projected in graphical curves on compendious table-forms, and then photographed by himself,—it would appear that these two months, June and July of 1884, were peculiarly unfortunate for sunshine. For not only was the preceding month of May bright with frequent sun, but the following month of August was the brightest and sunniest month of that, or any name which had occurred in the South of England for years.

And yet it would have proved dangerous to trust to that precedent for another campaign, as in the very next year (1885), it was the month of July that proved to be the most admirably sunny; and to a degree far beyond both May and June on one side of it, and August and September on the other. —Subsequent Note. C.P.S.

page 531 note * This note of size refers to the drawings for the plates. The actual prints, for economy's sake, are only one-third the size.

page 542 note * It seems by a recent publication from Upsala, that M. Thalen with prisms, saw the clear duplicity of the linelets of Great B's preliminary band much better than did M. Angstrom with a small grating, mounted on a theodolite stand. In fact the latter did not see them to complete identification; and in his extreme anxiety not to pass beyond the modesty of observation and the truth of nature, disputed long before he would allow his friend M. Thalen to draw these linelets double, as he saw them without any doubt, on the manuscript for the immortal “Normal Solar Spectrum.” They were however so drawn at last by M. Thalen, and were so engraved by the lithographer; but on his sending a proof of his work for correction to M. Angstrom, then on his death-bed, the dying philosopher, in his over conscientious desire not to exaggerate what he had really seen, took a pencil and filled in therewith the narrow spaces between the double members of each linelet; the engraver imitated the granular pencil markings; and that is the origin of the shading by dots, quite anomalous in spectroscopy, to be seen now on the finally engraved and published Atlas of the Normal Solar Spectrum, in its particular plate representing that preliminary band of the great B line.