( 206 ) 
An Adjustable Index Point for the Scale to be used as 
Marker. By W. K, Bridgman, 
In carrying out the principles laid down by tlie committee 
appointed by the council of the Microscopical Society, I have 
succeeded in producing an arrangement capable of doing 
double duty — serving as a " marker/' and, at the same time, 
being an index to the scale as a " finder " — so that either or 
both may be used upon the same object at any time without 
requiring a separate carrier, or interfering with any of the 
arrangements either of the slide or the object-glass. 
Now, although a mark upon the label, or on the end of 
the slide itself, may be held to be inadmissible as a permanent 
record, abundant proof has already been afforded that, by the 
present contrivance, much time may be saved, and the ordi- 
nary use of the microscope greatly facilitated. 
I look upon the objects we are seeking to attain as two- 
fold: 
1st. To save one's own time; and 
2d. To secure identity, either for oneself, or to enable 
other observers to find with certainty the particular speci- 
mens intended for their examination. 
As securing both these important objects, I oflPer a plan 
which is almost instantaneous in action, both for marking" 
and for " finding," and so easy of application, that it may 
readily be used by the veriest tyro in microscopic manipula- 
tion. It is also simple in construction, and capable of being 
applied to every form of instrument. But as very few micro- 
scopists are mechanics, no plan can be fully carried out 
unless our London makers take up the subject, and include 
finders in the purchasable furniture of the microscope. 
The method of arranging the index, as described in the 
report given in your number for October last, p. 95, leaves 
the space between this and the centre of the field an arbitrary 
distance. In our own plan, this space is fixed at one inch 
from the object, in a line parallel with the lower edge of the 
slide. The reason for taking this standard of measurement 
is that, as the ordinary slides (three inches by one) contain 
three square inches, allowing the centre inch for the recep- 
tion of the objects and their cover, a square inch will remain 
at each end, to be used either for the label as a marker, or to 
be covered by the scale as a finder ; and any two points, one 
inch apart in the same horizontal line (measuring from any 
point in the middle inch to any position in the other inch at 
