93 
movable on an upright by rack-work, and adapted for fitting 
over the microscope, which is described and recommended in 
this little hook. The hook may be had of Mr. David Nutt, 
foreign bookseller, Bedford Street, Covent Garden. 
Micro-Photography. By M. Jules Girard. — I have re- 
cently taken some pictures, the result of powerful enlarge- 
ments of diatoms varying from 800 to 1200 diameters. 
To obtain clear objects suitable for enlargement, it is 
necessary to establish a relation between the lens and 
the length of the camera ; and the more powerful the 
lens, and longer the camera used, the greater will be this 
relation. There exists, however, a very variable limit, which 
is incapable of being passed without altering the sharpness 
of the object, and which, is the result of experimental trials 
between these two combinations. As the intensity of the 
light diminishes proportionally to the distance of the object, 
it is necessary to have recourse to a condenser often com- 
posed of several lenses corrected so as to prevent distor- 
tion, which gives sufficient illumination to impress the 
sensitive surface. The focussing must be rigorously exact, 
as the most inappreciable digression of the microscopic 
screw is sufficient to injure the sharpness of the object. 
If enlargements of extraordinary size are required, a pro- 
cess similar to that used for making ordinary photographic 
enlargements may be employed. A small negative may first 
be obtained upon a tbin strip of glass, which is afterwards 
magnified by means of the microscope. This method is a 
very delicate one, and necessitates very careful focussing 
with a magnifier, in order that the most minute details may 
be rendered as sharply as possible. In developing there is 
likewise the difficulty of obtaining a suitable degree of inten- 
sity for the object : if the process is pushed too far, the light 
will be unable to penetrate ; if the development is insufficient, 
the negative will lack clearness. Thus the pictures taken 
direct possess the double advantage of being easy to produce, 
and more exact copies of the original. — A Paper read before 
the French Photographic Society, extract from ‘ Scientific 
Opinion ,’ No. 6. 
On taking Temperatures in Connection with the Micro- 
scope. Bv Th. Engelmann. 8 pages. Max Schultze’s Archiv, 
3rd part,' 1868. 
A New Hot-Plate for the Microscope. By Dr. Alexis 
Schklarewski. 3 pages. Max Schultze’s Archiv, 1868, 3rd 
part. 
Hcematoxylin-Colour. By H. Frey. — Max Schultze’s 
Archiv, 1868, 3rd part. 
