230 Royal Society :— 
shadows light and the light parts dark ; consequently, in magnifying 
a negative with the intention of still producing a negative, an inter- 
mediate transmitted positive must first be taken, and this in its turn 
magnified, when it will produce a negative. 
The relative distances of the negative and focusing glass from the 
intermediate lens were so adjusted, that an image of the negative, 
enlarged to about two diameters, was thrown upon the ground glass, 
care being taken that the light from the sky was reflected parallel 
through the centres of the negative and lens by means of the mirror. 
The aperture of the lens was then stopped down to half an inch by 
means of a diaphragm, and the focus most carefully obtained by 
sliding the end of the large camera in or out. I found it necessary 
to verify this by experimental trials at different distances on each 
side of the observed focus, as it was difficult to judge accurately with 
the eye on the ground glass, owing to the roughness of the latter and 
the feebleness of the light. 
A picture, or rather many pictures, were now taken, and the one 
which by transmitted light most truthfully resembled a paper print 
from the small negative was reserved for further magnifying. This 
was effected absolutely in the same manner as the former : the nega- 
tive being removed and the positive being placed in its stead, a further 
magnifying gave a large-sized negative. 
Although this process seems very simple, it is impossible to esti- 
mate the difficulties, unless by an actual repetition of the experiment, 
which I had to overcome before arriving at the beautiful result which 
I have the honour to lay before the Society. The double copying 
had a tendency to slightly exaggerate the effect of light and shade, 
and this could only be obviated by exposing the plates for such a 
time, that with the feeble light at my command it was verging on 
decomposition ; particles of dust, too, seemed most pertinaciously to 
fix themselves on the prominent mountains, giving rise to craters 
where none should be; and even my finished pictures are not per- 
fectly free from these faults, although each negative is the repre- 
sentative of a month’s work and upwards of a hundred failures. 
I doubt if much better photographs of our satellite can be taken 
by the way I have pursued. The future of lunar photography lies 
in another direction: the image must not be received on a sensitive 
plate and this copy submitted to an after process of magnifying. 
Defects quite imperceptible to the naked eye on the small negatives, 
are expanded into great blotches when magnified. In fact, upwards 
of a dozen seemingly equally good negatives with which I started, 
have, with but one or two exceptions, shown spots when enlarged. 
The magnifying must be conducted simultaneously with the pho- 
tographing, either by having the eyepiece on the telescope, or better 
still, by having a proper arrangement of lenses to throw a magnified 
moon image at once on the collodion. The difficulty of want of 
light could not be any objection, as supposing the enlarged image 
to be equal to those which I have now taken, that would be an 
increase of area of about twenty times, consequently 20 x 6 seconds, 
or 2 minutes, would represent the average time of exposure; a pe- 
