780 : MICROSCOPY. 
trated description of a most important piece af apparatus. He un- 
dertakes to avoid the difficulties of the method of drawing by the - 
camera lucida by substituting an instrument (Fig. 153) which shall 
present a fixed though large ratio between the movements of the 
pencil point on the paper and of a given point in the focus of 
the eye-lens of the ocular. A method previously in use and very 
easily used, for enlarging or reducing drawings is combined now, 
for the first time, with the microscope. Two parallelograms of 
light rods are constructed having their adjacent sides inflexibly 
connected with each other. All the intersections of the sides are 
pivoted so as to have a free horizontal motion, and the intersec- 
Fig. 153. - 
tion of the two parallelograms is made a fixed point by screwing 
it to a brass plate which slides into the ocular in the usual posi- 
tion of a micrometer. The pivot at the outer end of the large 
parallelogram carries a pencil, and in the corresponding position 
in the small one is a glass plate with cross-lines ruled upon it. 
When in use in the microscope the cross-lines are in focus of the 
eye-lens, and the pencil rests upon a sheet of paper suitably 
Supported near the top of the compound body. The pencil BR 
be so moved as to cause the intersection of the cross-lines to pass _ 
Over the parts of the object desired to'be delineated. Such a 
drawing would probably surpass in accuracy any other that could 
be made. 
