J. J. Woodward on Photo-micrography. 193 
The plate holder is movable backward and forward on the 
walnut frame on which the microscope stands, its maximum dis- 
tance from the stage of the microscope being nearly nine feet. 
To permit ready focusing at distances greater than the length 
of the arm, a wooden rod #ths of an inch in diameter and capa- 
ble of easy rotation runs the whole length of the right side of the 
frame. ‘The milled head of the fine adjustment of the microscope 
is grooved, and a small grooved wheel in the end of the rod 
permits the two to be connected with a band. The operator 
standing at any part of the frame can therefore manipulate the 
fine adjustment by simply turning the wooden rod in his fingers. 
The arrangements of light, position of object, coarse adjust- 
ment, &c., are made by the operator, who stands by the micro- 
scope, which has a suitable eye-piece adjusted, and observes the 
object in the usual way; afterwards, removing the eye-piece 
and going to the plate holder, the final focusing is made by 
means of the wooden rod, the image being viewed with a focus- 
ing glass on a piece of plate glass held in the same frame which 
is to receive the sensitive plate. 
he cell containing the ammonio-sulphate of copper hangs 
outside the shutter over the hole by which light is admitted. 
It not only excludes the unnecessary illuminating rays, but pre- 
vents danger to the objective from the concentrated solar heat 
and permits the eye of the operator to view the objects about 
to be copied without fatigue or injury. Latterly a plate of alum 
has also been used to exclude solar heat especially during any 
temporary removal of the ammonio-sulphate cell. The chemical 
processes employed are well known to all photographers. With 
the above apparatus, it has been found that the best defined 
pictures are obtained when the distance employed with any ob- 
jective does not exceed three or four fee é 
The achromatic concave used as a substitute for the eye-piece 
is a combination of somewhat more than half an inch transverse 
