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Half-hours with the Telescope - Being a Popular Guide to the Use of the Telescope as a - Means of Amusement and Instruction. by Richard Anthony Proctor
page 87 of 115 (75%)
a better set of views than any of the others. But there is an amount of
detail in Mr. Dawes' views which renders them superior to any yet taken.
I must confess I failed at a first view to see the full value of Mr.
Dawes' tracings. Faint marks appeared, which I supposed to be merely
intended to represent shadings scarcely seen. A more careful study
shewed me that every mark is to be taken as the representative of what
Mr. Dawes actually saw. The consistency of the views is perfectly
wonderful, when compared with the vagueness and inconsistency observable
in nearly all other views. And this consistency is not shown by mere
resemblance, which might have been an effect rather of memory
(unconsciously exerted) than observation. The same feature changes so
much in figure, as it appears on different parts of the disc, that it
was sometimes only on a careful projection of different views that I
could determine what certain features near the limb represented. But
when this had been done, and the distortion through the effect of
foreshortening corrected, the feature was found to be as true in shape
as if it had been seen in the centre of the planet's disc.

In examining Mr. Dawes' drawings it was necessary that the position of
Mars' axis should be known. The data for determining this were taken
from Dr. Oudemann's determinations given in a valuable paper on Mars
issued from Mr. Bishop's observatory. But instead of calculating Mars'
presentation by the formulæ there given, I found it convenient rather to
make use of geometrical constructions applied to my 'Charts of the
Terrestrial Planets.' Taking Mädler's start-point for Martial
longitudes, that is the longitude-line passing near Dawes' forked bay, I
found that my results agreed pretty fairly with those in Prof. Phillips'
map, so far as the latter went; but there are many details in my charts
not found in Prof. Phillips' nor in Mädler's earlier charts.

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