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The prominences are examined with an equatorial, driven by clockwork, as follows:—Having discovered the exact focus of the telescope, by receiving the solar image on a card.in place of the eye-piece, place the slit exactly at this spot. Now revolve the spectroscope till the slit is at right angles to the sun’s limb. Notice that the sharp edge of the sun is seen across the slit, which at first may be narrow. Two spectra will be seen, the limb of the Sun giving a bright band of colour with dark lines, and side by side with this is a faint spectrum from the earth’s atmosphere. If the slit be carried round the edge of the Sun* by the independent movements of the telescope, coloured lines will be seen on the faint spectrum directly the slit is over a prominence. These lines, which correspond to the solar lines, C, F, and D3, will vary in length as the slit is carried across the prominence ; and this variation will enable the exact shape to be ascertained. One end of the line being against the bright spectrum, will enable the vertical shape to be indicated by the variations of the other end. If the slit be now carried across the prominence at right angles to the former direction the horizontal shape can be ascertained in the same way. Should the line appear separate from the solar spectrum, that part of the prominence will be detached from the Sun.

If there is sufficient dispersion to nearly obliterate the fainter spectrum, the slit can be opened as widely as the light of the bright spectrum will allow, or this may be toned down by coloured glasses, and the entire prominence then seen at once, instead of in sectional lines. There will be an image of the prominence where each bright line was before situated. Either of these images can be seen in the field accordingly as the red, yellow, or bluish-green part of the spectrum is brought into view.

The method of viewing other celestial objects depends on the employment of a slit. If a slit is used it should first be sharply focussed by the eye-piece. The star having been found, is focussed to a line by the cylindrical lens, and the slit is placed over and upon this line. The spectrum can then be sharply focussed by means of the separate adjustments of the spectroscope and telescope. When once the correct position of the spectroscope has been ascertained, the above adjustment need not be repeated, but the object may be found through the prisms, and delicately focussed as usual.

If there is no slit, remove the tube containing the prism, and focus the star to a line by the cylindrical lens, either with or without an inner eye-piece, the eye being placed exactly where it would be if the prism was being employed. Having replaced the prism the spectrum can be delicately focussed to a sharp edged band, with the dark lines clearly visible, by means of the rack of the telescope. The method of viewing any other celestial object is similar in all respects, except that when the object cannot be focussed to a line, it should be elongated by the lens as much as possible.

. The width of the slit should be regulated to the brightness of the subject and the sharpness of the lines : when using a cylindrical lens it may be opened very widely, in order to admit as much light as possible.

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La langue de reconnaissance de l'OCR est l'Anglais.

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