are supposed to be seen with the
same "power."

The observer must not expect to see the details presented in the views
of Mars with anything like the distinctness I have here given to them.
If he place the plate at a distance of six or seven yards he will see
the views more nearly as Mars is likely to appear in a good three-inch
aperture.

The chart of Mars is a reduction of one I have constructed from views by
Mr. Dawes. I believe that nearly all the features included in the chart
are permanent, though not always visible. I take this opportunity of
noting that the eighteen orthographic pictures of Mars presented with my
shilling chart are to be looked on rather as maps than as representing
telescopic views. They illustrate usefully the varying presentation of
Mars towards the earth. The observer can obtain other such illustrations
for himself by filling in outlines, traced from those given at the foot
of Plate VI., with details from the chart. It is to be noted that Mars
varies in presentation, not only as respects the greater or less opening
out of his equator towards the north or south, but as respects the
apparent slope of his polar axis to the right or left. The four
projections as shown, or inverted, or seen from the back of the plate
(held up to the light) give presentations of Mars towards the sun at
twelve periods of the Martial year,--viz., at the autumnal and vernal
equinoxes, at the two solstices, and at intermediate periods
corresponding to our terrestrial months.

In fact, by means of these projections one might readily form a series
of sun-views of Mars resembling my 'Sun-views of the Earth.'

In the first view of Jupiter it is to be remarked that the three
satellites outside the disc are supposed to be moving in directions
appreciably parallel to the belts on the disc--the upper satellites from
right to left, the lower one from left to right. In general the
satellites, when so near to the disc, are not seen in a straight line,
as the three shown in the figure happen to be. Of the three spots on the
disc, the faintest is a satellite, the neighbouring dark spot its
shadow, the other dark spot the shadow of the satellite close to the
planet's disc.

HALF-HOURS WITH THE TELESCOPE.

CHAPTER I.

A HALF-HOUR ON THE STRUCTURE OF THE TELESCOPE.

There are few instruments which yield more pleasure and instruction than
the Telescope. Even a small telescope--only an inch and a half or two
i