334 
PROFESSOR PHILLIPS ON SOME PARTS 
my dwelling till (in 1860) the ground was arranged about the museum, so as to give 
me the requisite space and security close to the house which had been appointed for 
me by the University. I then arranged with Mr. Cooke for a new telescope of 6 inches 
aperture, to be protected in a well-planned observatory, the construction of which was 
aided by the Royal Society. I now propose to give a short notice of some of the results 
of my work with this instrument, in connexion with remarks on the most advisable 
course to be followed by other surveyors of the moon. 
In making drawings of ring-mountains on different parts of the moon’s disk, the 
artist will be much aided by a projection of the mountain-border on the scale intended, 
from a few measures, with its proper figure due to the latitude and longitude. Eye- 
drafts not thus controlled are apt to become absurd, by the heedless substitution of an 
ideal circle for a real ellipse. Thus I have seen Gassendi forgetfully represented in 
more than one skilful drawing. Even with the advantage of such a projection (of which 
I give an example for Gassendi, No. 5) very considerable difficulties occur. One is the 
variation of outline caused by the displacement of the boundary of light and shade, first 
when the incidence of light varies through different angles of elevation of the sun, and 
next when the moon’s position causes her to receive the light at the point observed on 
a different lunar azimuth. Even on so great a ring as Copernicus the variation of the 
outline as given by different artists is remarkable — hardly any one agreeing with what 
is really the most accurate drawing of all, that by P. Secchi ; and that represents, not 
a simple ring, but a seven-angled outline. Dates must always be annexed to the figures ; 
and as it is rarely possible to complete a good drawing of a large crater, except in two 
or three lunations or more, it becomes very essential that a bold free sketch be made of 
the moon’s shadows to control the special work. 
Strictly speaking, there should be at least three drawings of a ring-mountain — in 
morning light, at midday, and in evening. It would be better to have five drawings, 
one at sunrise and another at sunset being added to the three already named. It will 
be found most convenient to make the drawings within two hours of the moon’s meridian 
passage. 
Shadows thrown from objects on the moon have exactly the same character as those 
observable on the earth. They are all margined by the penumbra due to the sun’s dia- 
metral aspect; this is always traceable except very near to the object; but in conse- 
quence of the smaller diameter and more rapid curvature of the moon’s surface, the 
penumbral space is narrower. At the boundary of light and shade, on a broad grey 
level tract, the penumbral space is about nine miles broad, quite undefined, of course, 
but perfectly sensible in the general effect, and worthy of special attention while 
endeavouring to trace the minute ridges (of gravel 1) or smooth hanks (of sand X), which 
make some of these surfaces resemble the postglacial plains of North Germany, or 
central Ireland, or the southern parts of the United States, which within a thousand 
centuries may have been deserted by the sea. 
To the same cause is due the curious and transitory extension of half-lights over some 
