EEE MICROSCOPE 
DECEMBER, 1897. 
NUMBER 60 NEW SERIES 
Spider-Lines. 
By F. L. 0. WADSWORTH, 
YERKES OBSERVATORY. 
It would be well to use for the cross-wires in our in- 
struments something of amore reliable and permanent 
nature than the usual spider-web. This, although very 
tine and strong, has so many and such grave disadvan- 
tages as to make one wonder how it has ever been toler- 
ated as long as it has, Formerly perhaps it might have 
been said that there was no thoroughly satisfactory sub- 
stitute; even the finest metal wires prepared by the so- 
called Wollaston process being too coarse, and silk having 
the same disadvantages as spider-line itself in the way of 
hygroscopicity and semi-translucency. Now, however, 
the invention of the quartz fibre by Boys has provided 
us with something which is not only entirely unaffected 
by atmospheric changes, but also superior to spider-line, 
and, in fact, to all other known fibres, in strength and 
fineness. The quartz fibres themselves are transparent : 
but this difficulty is removed, and the fibers made more 
easily visible for handling and mounting as well, by sil- 
vering them by any of the well-known silvering processes. 
When properly silvered, they are perfectly opaque, even 
in the most strongly illuminated field. 
I do not know who first proposed the use of silvered 
quartz fibres but their obvious advantages must have 
suggested their use for this and many similar purposes— 
