ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
519 
To the amateur, who has been using but lamplight for his exposures, 
it is suggested that he avail himself of some bright “ off-day ” to give 
sunlight a trial. If the mirror of the Microscope be of good size, it 
will be only necessary to make an arm on which to support the removed 
mirror outside some southerly exposed window, since it is desirable to 
have much more distance between the mirror and the stage than would 
be possible were the mirror attached in its usual place. Where the 
Microscope mirror is too small to be satisfactorily used, a rectangular 
wood-framed looking-glass is readily mounted with the aid of a few 
strips of wood, so as to turn about both axes. 
The rays from the plane side of the mirror are passed through a 
condensing lens (of 8-10 in. focus, if possible), so placed that they are 
brought to a focus before reaching the plane of the object. The exact 
position of the condensing lens is a matter of experience; usually, 
however, the most favourable illumination is obtained at that point 
where the field is still uniformly illuminated, just before the rays form 
an image of the source of light ; the nearer the rays are focused, the less 
disturbance from diffraction rings. Ordinary objectives will require the 
employment of monochromatic light — produced either by a deep blue 
solution of ammonio-sulphate of copper, or by the green glass screen 
already mentioned — since the optical and actinic foci do not usually 
coincide. Powers up to the 3/4 in. will require no further condenser; 
with the 1/4 or 1/6 objectives, the low power (1 or 3/4 in.)J serves with 
advantage as an achromatic condenser, when attached to the substage. 
The Abbe condenser, although so important for refined microscopical 
investigation, is not adapted to photography unless a very wide cone of 
light is desired, which, for the majority of preparations, is a decided 
disadvantage ; a low-power objective, used as a condenser, will generally 
be found more satisfactory than the Abbe with a small diaphragm. 
The simple apparatus indicated, when properly handled, will produce 
excellent work with such powers as the amateur is likely to employ ; 
focusing the image by the monochromatic light, and avoiding over- 
exposure, being the points especially requiring experience. When it is 
remembered that seconds, with very slow plates, usually suffice for the 
minutes with rapid ones of an exposure by lamplight, the intensity of 
the actinic power of the sunlight will be somewhat appreciated Some 
simple arrangement, by which the rays from the mirror may be cut off 
with sufficient rapidity, will suggest itself ; an effective one is a small 
shutter, turning at one end on a screw and covering a circular opening 
in a board, through which the rays from the mirror pass ; the rapidity 
with which the sun’s image from a fixed mirror becomes decentered 
necessitates a readjustment of the light just before each exposure, but 
the patience thus exercised will be more than repaid in the character of 
the resulting negatives. 
Microphotographs of Wood Sections. — An interesting communica- 
tion on this subject was recently made by MM. Thil and Thouronde 
to the French Photographic Society. Microphotographs to the num- 
ber of about four hundred were executed to the order of the Minister 
of Agriculture. M. Thil, Inspector of Government Forests, has, in 
very precise language, pointed out the reach of this application of 
photography, which permits of the classification of woods in families 
