. The book of photography; practical, theoretical and applied. pse. The former is themore important, as then a dark shadow ofthe moon, called an umbra, is cast uponthe earth, as shown by Fig. 812. Thisdark shadow moves across the earths sur-face, and takes about a minute and aquarter to transfer its area completely GIG THE BOOK OF PHOTOGRAPHY. over any place that lies on the diameterof the shadow. While the sun is thuscompletely obscured, and all direct raysfrom the photosphere are consequentlycut off, photographs may be taken byordinary means of the solar surroundingsand appendages, which are
. The book of photography; practical, theoretical and applied. pse. The former is themore important, as then a dark shadow ofthe moon, called an umbra, is cast uponthe earth, as shown by Fig. 812. Thisdark shadow moves across the earths sur-face, and takes about a minute and aquarter to transfer its area completely GIG THE BOOK OF PHOTOGRAPHY. over any place that lies on the diameterof the shadow. While the sun is thuscompletely obscured, and all direct raysfrom the photosphere are consequentlycut off, photographs may be taken byordinary means of the solar surroundingsand appendages, which are absolutely in-visible under other circumstances owingto the overpowering radiation of the sun. External Aids. Since the light emitted by the gorgeousappearance of the suns corona, as it istermed, is too faint to be all caught in thesmall time available for exposure, photo-graphic observations have to be supple-mented by drawings obtained by otherobservers. As the appendages arecoloured, the various shades are noted atthe same time. It can be well understood. FiiT. 812.—Umbra C\used by Solak :. high dispersion given by the two deviation of the tube from theoriginal path of the rays is 66°. At thetotal solar eclipse in 1900, a largerprismatic camera was also tried. Theobject glass had a focal length of 20 the image is formed at the focus,the diverging colours travel three timesas far before they unite to form the spec-trum. Therefore a single prism withthis instrument will give a larger disper-sion than two similar prisms with thesmaller one, with about half the devia-tion. Attached to the tubes of these in-struments are the finders. The type ofphotograph obtained has been previouslydescribed. A diagrammatic reproductionis given showing how the repetition incolours of the shape of the chromospheregives a spectrum (see Fig. 807). Theprisms used must naturally be very biggest was 9 in. high, with a refract-ing angle of 45°. SiDEROSTAT AND
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectphotography, bookyear
