236 
POPULAR SCIENCE REYIEW. 
with those, so familiar to every experienced observer, in which 
hard, clear definition is combined with unsteadiness of image ; 
the irregular refraction of the atmosphere producing the very 
same effect that the undulations of surface would on the posi- 
tion of an object seen, otherwise with great distinctness, in the 
bed of a running stream. In such a state of air — the best 
oftentimes that an observer is fortunate enough to meet witl> 
in the course of many nights — photography would be confusion, 
while good drawing is perfectly practicable. 
But then, it scarcely need be added, it ought to be good 
drawing. Not that rough sketches may not prove occasionally 
of value, when they contain clear evidence of some previously 
unnoticed object ; but the student ought to be especially 
warned against a facile carelessness of execution, which must i 
prove unsatisfactory to others, and ultimately to himself. And 
the professed artist is perhaps especially likely to be thus | 
betrayed into error. Of course, before he sets to work upon ' 
any celestial object, he will have laid aside all thought of 
making a pleasing picture ; but he may still be misled from | 
being habitually conversant with that essential principle of ' 
art, which teaches us that likeness is more connected with j 
breadth of effect, than with elaboration of detail. In the ! 
present case, however, it is on accurate minuteness that we j 
have to depend for our hope of discovery; experience contra- ' 
venes all reasonable expectation of physical change on a great ; 
scale in our own days, and our knowledge of the real nature of j 
the lunar surface, and any operations that may be in progress I 
there, must depend on the faithful representation of the ■ 
smallest objects that our telescopes are capable of showing with i 
distinctness. j 
The principal requisites of good drawing, as applied to the ! 
lunar surface, maybe easily specified. They are (1) correct- | 
ness of form. It would seem almost superfiuous to specify | 
this, but for the glaring inaccuracy in this respect, which is j 
occasionally apparent even in drawings which ought, from 
their advantageous circumstances, to take a high rank. And 
it is here that a knowledge of effect and perspective becomes 
of great value. Although we demand a resolved fidelity, which 
is determined to represent everything just as it appears, how- 
ever anomalous that appearance may be, and although nothing 
could easily be worse than an attempt to force a delineation 
into accordance with the rules of art, yet it is certain that a 
previous apprehension of the real nature of what is seen will 
often give material aid in preventing mistakes and facilitating 
observation. When, for instance, we know that every circle 
lying in a certain direction as regards the line of sight must 
be projected into an ellipse of known proportion and position. 
