onomical
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.

But, undoubtedly, for the possessor of a moderately good telescope there
is no way of viewing the sun's features comparable to that now to be
described, which has been systematically and successfully applied for a
long series of years by the Rev. F. Howlett. To use his own words: "Any
one possessing a good achromatic of not more than three inches'
aperture, who has a little dexterity with his pencil, and a little time
at his disposal (all the better if it be at a somewhat early hour of the
morning)" may by this method "deliberately and satisfactorily view,
measure, and (if skill suffice) delineate most of those interesting and
grand solar phenomena of which he may have read, or which he may have