The simplest method of observing the sun is to use the telescope in the ordinary manner, protecting the eye by means of dark-green or neutral-tinted glasses.  Some of the most interesting views I have ever obtained of the sun, have resulted from the use of the ordinary terrestrial or erecting eye-piece, capped with a dark glass.  The magnifying power of such an eye-piece is, in general, much lower than that available with astronomical eye-pieces.  But vision is very pleasant and distinct when the sun is thus observed, and a patient scrutiny reveals almost every feature which the highest astronomical power applicable could exhibit.  Then, owing to the greater number of intervening lenses, there is not the same necessity for great darkness or thickness in the coloured glass, so that the colours of the solar features are seen much more satisfactorily than when astronomical eye-pieces are employed.

In using astronomical eye-pieces it is convenient to have a rotating wheel attached, by which darkening glasses of different power may be brought into use as the varying illumination may require.

Those who wish to observe carefully and closely a minute portion of the solar disc, should employ Dawes’ eye-piece:  in this a metallic screen placed in the focus keeps away all light but such as passes through a minute hole in the diaphragm.

Another convenient method of diminishing the light is to use a glass prism, light being partially reflected from one of the exterior surfaces, while the refracted portion is thrown out at another.

Very beautiful and interesting views may be obtained by using such a pyramidal box as is depicted in fig. 11.

[Illustration:  Fig. 11.]

This box should be made of black cloth or calico fastened over a light framework of wire or cane.  The base of the pyramid should be covered on the inside with a sheet of white glazed paper, or with some other uniform white surface.  Captain Noble, I believe, makes use of a surface of plaster of Paris, smoothed while wet with plate-glass.  The door b c enables the observer to “change power” without removing the box, while larger doors, d e and g f, enable him to examine the image; a dark cloth, such as photographers use, being employed, if necessary, to keep out extraneous light.  The image may also be examined from without, if the bottom of the pyramid be formed of a sheet of cut-glass or oiled tissue-paper.

When making use of the method just described, it is very necessary that the telescope-tube should be well balanced.  A method by which this may be conveniently accomplished has been already described in Chapter I.