Maddox_, on the Delineation of Microscopic Objects. 11 
be in part somewliat verified by the prints for your obser- 
vation that accompany this paper. Untouched, unpressed^ 
prepared with little care, they are simply intended to show 
the general and the partial application of photomicrography, 
and, however feebly they may represent either, the infancy 
of the art must be remembered, and the failings forgotten in 
the effort to render them more acceptable. 
The midge, sand-hopper, Entomostraca, section of the 
pith of Hydrangea, of scalariform duct of Macca or Racca, 
the seaweeds, Fragilaria and Zygnema, will sufficiently 
illustrate its first application, and the prints of the several 
diatoms will show its employment in its second character ; 
the former being casually mounted without preparation, 
the latter as commonly prepared by microscopists. 
The apparatus may briefly be stated as a microscope 
attached by means of telescope tubes to an expanding 
camera, the whole fixed on a stout board, four feet six 
inches long, supported by double triangle legs ; the illumina- 
tion is either by a plane or concave mirror, or Abraham^ s 
achromatic prism, preference being given to the latter; the 
condensing lens, a Coddington of small angular aperture. 
Strong sunlight, if possible, is employed in all cases; a 
slow collodion, iron developer, and the ordinary means used 
to strengthen the negative, if, on examination by a lens, the 
details be seen sufficiently perfect. Slight obliquity of the 
light has generally been attempted, especially when the 
surface of the object was not flat. The long eye-piece has 
been occasionally used, and I think, gives what is commonly 
called depth of focus,^^ but certainly at a little loss of defi- 
nition. The main difficulty lies, not in obtaining a negative, 
but one that, when nicely printed, gives something of the 
character of the object when seen by a weak, reflected light; 
for the prints may be said to scarcely resemble objects seen 
by transmitted light. In fact, we are hardly yet familiar with 
the representation of microscopic objects by its means, and 
therefore we rather at once unjustly revert to the illustra- 
tion by engraving for a comparison. There is a considerable 
danger of producing a weak negative from over-exposure 
where the field is not well filled by the object, and especially 
if we seek to render the details when the object itself is 
coloured. Success appears to me much to rest, cceteris 
paribus, in the illumination of the object, in the plans for 
which there is a wide field, from ordinary daylight to con- 
centrated sunlight, from the mirror to the prism, from 
the achromatic to the simple condenser, from direct to 
oblique transmitted light, from concentrated to obliquely 
