On page 310, current volume, I noticed an article alluding to a forme;:' one on page 189, "Storms on the Sun," for the purpose of showing simultaneous "electric disturbances " about our planet. which gives further hints of a simple and good method for obtaining It comparative correctness of statistics of the solar disturbances noticed through a telescope, by means of reflecting them upon a screen. I wil quote two paragraphs : "Believing that a simple means of observing and accurately recording solar phenomena could induce amateurs as well as professionals, to keep such records, I respectfully propose tiJ- f-jllowing method, which I never have heard of being thus used by any one before. Take an astronomical reflectil'g telescope with a Huyghenian eye piece, into a dark room, direct it on the sun through an aperture, push in the eye piece until it is between the object glass and its principal focus, now place a fine white screen at some distance from the eye piece and focus sharply, a large, clear, well defined, erect image of the , sun is thus obtained, which may be enlarged or diminished at will, arrange the aperture, increasing or decreasing the light, until the finest details are visible. , The sun can now be examined without darkening glasses, and by several persons at once. "For uniformity ol record I would suggest the adoption of one regular L,70e, say a circle inscribed within one square foot divided . nto square inches ; the space being numbered from right to left, and from top to bottom. The exact position of any disturbance observed could thus be easily ascertained and recorded." The idea of reflecting solar spots, etc., upon a screen, is excellent but not new. While attending the Elmira Astronomical Observatory, at Elmira, N. Y., during the spring of 1862, and desiring to make some solar observations, this plan was adopted for most of them, but was not original with me. The writer is under the impression that this process is old. I made a long series of observations on the sun at this time, and with considerable ert made a different sketch of the sun's appearance every day, when the weather would in any way permit, and at exact time. My reflected repriisenta-tion of the sun was about ten feet in diameter, and my pictures were made one foot in, diameter. The central spot or nucleus was made with black ink, the penumbra with l!jad pencil, while the faculre were represented with white crayon. It must he understood that straw colored paper is essential for the best representations. The disturbances of the solar photosphere are very interesting to young students, and are becoming more interesting with all astronomers, as the time approaches for the great expected display of spots of 1871, wlxen, fiom all accounts, the 8:1 is to become q uite " speckled," or at least great magnetic disturbances are looked for. Sometimes (though rarely) no spots are visible on the sun, again, one may he seen, at other times quite a large number may be seen scattered all along the equatorial belt of 70 degrees in width. Spots outside of this belt are very rarely seen. The disturbances of the luminous portion of the solar atmosphere, if I may be allowed to use the term, are noticed upon the screen n curly streaks of bright light, in irregular shapes, resembli waves on a lake during a sunny, windy day, and particularly plam near and around tlie spots, reBem-bling much the tumult and circular waves round a place where a large stone has beja d roppedinto a pon d of wator . I noticed, whenever I sa' a good deal of facul disturbance, in any quarter, there generally followed spots 11 a few hours. This s so characteri sti c t h at it l s easy to foretell the appearance of some larger spots, one or two days b t()fore tliey appear around the approachlng limit, that i s, before they appear in sight, as it is supposed all know the sun revolves on bis axis once in 25-34 days, which continually brmgs new spots into view. Some days scarcely any facular disturbance could be noticed on the ten-feet reflection on the screen, while on other days it could be distinctly seen covering the whole zone of 35 degrees each side of the equator. On January 3rth, the same season (1862) my brother, in company with myself, noticed the whole face of the solar orb covered with enormous disturbances of the photosphere. from pole to pole, and from limit to limit, entirely mottled with wave-like shades. On this occasion fifteen spots were visible, two of which were very large ; undoubtedly a more powerful glass would have revealed many more. The fuculre on this occasion like most other days were more agitated and greater as they approached the equator. The instrument used in these observations was Fitt's 8-in. Acromatic Equitorial Telescope, erected by Professor C. S. Farrar. I used a prismatic eye piece to reflect the object upon the screen. Although these representations were very good and convenient, yet I found I could get a finer line and more correct idea from views seen directly through the telescope, by using two or three colored glasses between the eye and eye piece. This is, however, a dangerous plan, as the colored glasses sometimes break from intensity of heat, and the loss of an eye may be the result, as has been the case before. Great care should be exercised in viewing the sun directly through a powerful telescope. The proposition of a checkered field upon which to thi'ow the image of the solar nrb seems to me good. The writer would kindly suggest in addition to the plan of the author of the article above mentioned, that the cross line check he made comparatively small and light, and be secured to the telescope, so that it will keep pace with the motion of the earth on its axis, and hold the whole picture upon the screen in juxtaposition, and not necessitate a constant adjusting anew of the telescope. as would be the case if the screen held the lines, having prepared everything in this manner, a comparatively accurate sketch of every visible dlstmbance can be conveniently made in a book, whose pages are correspondingly checked.
This article was originally published with the title "“How to Observe the Sun”" in Scientific American 21, 24, 375 (December 1869)