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. In
place, however, of a box carried upon the telescope-tube, a darkened
room (or true _camera obscura_) contains the receiving sheet.

A chamber is to be selected, having a window looking towards the
south--a little easterly, if possible, so as to admit of morning
observation. All windows are to be completely darkened save one, through
which the telescope is directed towards the sun. An arrangement is to be
adopted for preventing all light from entering by this window except
such light as passes down the tube of the telescope. This can readily be
managed with a little ingenuity. Mr. Howlett describes an excellent
method. The following, perhaps, will sufficiently serve the purposes of
the general observer:--A plain frame (portable) is to be constructed to
fit into the window: to the four sides of this frame triangular pieces
of cloth (impervious to light) are to be attached, their shape being
such that when their adjacent edges are sewn together and the flaps
stretched out, they form a rectangular pyramid of which the frame is the
base. Through the vertex of this pyramid (near which, of course, the
cloth flaps are not sewn together) the telescope tube is to be passed,
and an elastic cord so placed round the ends of the flaps as to prevent
any light from penetrating between them and the telescope. It will now
be possible, without disturbing the screen (fixed in the window), to
move the telescope so as to follow the sun during the time of
observation. And the same arrangement will serve for all seasons, if so
managed that the elastic cord is not far from the middle of the
telescope-tube; for in this case the range of motion is small compared
to the range of the tube's extremity.

A large screen of good drawing-paper should next be prepared. This
should be stretched on a light frame of wood, and placed on an easel,
the legs of which should be furnished with holes and pegs that the
screen may be set at any required height, and be brought square to the
tube's axis. A large T-square of light wood will be useful to enable