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In viewing objects with a reflecting telescope the small mirror sometimes forms a dusky horizontal band across the centre of the spectrum. We have lately found that by the introduction of a Barlow’s lens, very much under or over corrected, an image on one side of the focal point will be formed free from this band. On the other side it will of course be increased.

To view the combustion of a salt in a gas flame or spirit lamp Make a saturated solution of the salt, and into it dip a platinum wire bent to the loop, and introduce the wire and the solution which clings to it into the flame. If preferable a small piece of the salt or crystal can be fused whilst supported on the loop. Focus the slit by means of the sliding eye-piece, and direct the spectroscope to the flame. A slight alteration of focus and of the width of the slit may be necessary to distinctly show the bright lines. The same plan can be followed in viewing the Sun without a telescope, only the lines will be dark instead of light.

The small spectroscope about to be described forms a very convenient method of observing the spectra of meteors; for this purpose the spectroscope should be used by itself, and should consist of the prism and cylindrical lens alone.

A small right-angled prism is sometimes placed over part of the slit, in order that the spectrum of a known substance can be seen in the field, for comparison.

We have lately introduced a small direct vision spectroscope, which can be adapted to all varieties of spectroscopic investigation. A short description of this instrument may be useful.

HORNE & THORNTHWAITE’S MINIATURE UNIVERSAL SPECTROSCOPE.

This instrument consists of a series of direct vision prisms, a cylindrical lens, an adjustable slit, an achromatic lens to focus the slit; all enclosed in brass tubes, which, for astronomical purposes, can be affixed a low power eye-piece.

The instrument can be used in three forms ; with the focussing lens and slit, for general purposes; with the cylindrical lens alone, for examining the stars, nebulee, &c., with the aid of a telescope, and for viewing meteors, the Aurora Borealis, without such aid; and with the cylindrical lens and low power eye-piece for general observations of all astronomical phenomena, excepting those connected with the sun; the prism being, of course, always required. The second form cannot, perhaps, be used, unless there is a considerable amount of focal adjustment to the telescope, or a Barlow’s lens be employed; but the third will focus at the same position as the eye-piece would be if used by itself.

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