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 seen depicted, in various works on physical astronomy."[15] The method in question depends on the same property which is involved in the use of the pyramidal box just described, supplemented (where exact and systematic observation is required) by the fact that objects lying on or between the lenses of the eye-piece are to be seen faithfully projected on the white surface on which the sun's image is received.