58 On the Application of Photography, 
rays, it becomes necessary that the plane of the sensitive 
plate should coincide with the foci of these rays, and it must 
therefore be placed beyond the surface at which the best 
definition is seen ; this amounts to some distance with the 
lower combinations, and decreases with the increase of mag- 
nifying power. 
For the production of negative pictures the ordinary illu- 
mination is not sufficient, and recourse must be had to the 
sunbeam, which should be reflected upon the object by the 
plane mirror when powers are used not exceeding the quarter 
of an inch combination. It is not necessary here (when pro- 
ducing negatives by the sunbeam) to allow for the " over- 
correction " of the object-glass, but merely to focus the object 
carefully upon the ground-glass plate. 
With regard to the time required for the production of 
these photographs, unfortunately no precise rules can be 
given, since it must vary with the sensitiveness of the mate- 
rials employed. The larger group exhibited was produced 
by the " 1 inch object-glass," and the time given varied from 
ten seconds to one minute. The smaller group, representing 
" scales of Lepisma saccharina by the quarter inch and one- 
eight inch glasses, was taken with a more sensitive collodion ; 
and the time from ten to fifteen seconds." 
In the production of negative pictures (from which the 
paper specimens were obtained) a moment's exposure to the 
sunbeam is sufficient when using the lowest powers, and with 
the highest I have varied the time from five to ten seconds. 
In conclusion, I beg to submit this method which I have 
found so simple and successful, in the hope that the com- 
munication may be the means of directing attention to a subject 
both useful and interesting, and in the confidence that most 
satisfactory results will yet be obtained. 
Some Observations on the Structure of the Starch- Granule. By 
Geo. Busk, Esq., F.R.S. (Read Dec. 29, 1852.) 
" No substance has been more investigated, and yet of which 
there is less known, than starch. After the researches of ten 
years, in the course of which the most various views have been 
propounded on the nature of starch, and after all its character- 
istics as a proximate vegetable substance have been discussed, 
we are little or nothing in advance of the old point of view ; and 
although we may, perhaps, not be wholly without some addition 
to our knowledge in secondary points, we are still entirely without 
any sound reasons to suppose that we have arrived at the truth." 
This passage, from PoggendorfF's Annal., 1837, vol. xxxii. 
