Prof. Watiace’s Description of the Eidograph. 439 
passing an axis through the tubes of P the copying point of A, 
and 'T’ the tracing point of B. If this axis contained a copying 
pencil, it would make a reduced copy of the original, and P’, the 
copying point of B, would at the same time make a copy of this 
first copy ; if the intermediate copy be not wanted, it need not 
be made. If each instrument were adjusted so as to make a 
copy, reduced in the proportion of five to one, the copy made at 
P’ would be one twenty-fifth of the original. It is evident that 
two or even more reduced copies might be made at the same 
time from one original, by ‘using several instruments. I have not, 
however, made more than one at a time by two instruments. It 
was in this way that some of the etchings on copper referred to 
in this paper were made ; their sizes were 4, 1, +, and ;4; of the 
original. The place of the copying pencil was supplied by a steel 
point, which just cut through the varnish of the etching ground ; 
this was all that was required to allow the acid to act on the 
copper. 
