88 
Resistance. 
I. The resistance is proportional to the length. Connect 
B with 0 , 1 ) with E, A with F. Introduce at A and lead 
off at E. We have then a divided circuit joining A and E, 
one consisting of the two coils (1) and (2), and the other 
the coil ( 3 ) only one half the length and going in the oppo- 
site direction. But as there is no deflection the current 
through the first circuit of twice the length must be only 
one half that through the other to exert an equal force, i.e. } 
the resistance is doubled when the length is doubled. 
II. The resistance is inversely proportional to the cross 
section. Introduce at A, connect A with L, connect B with 
C and D with K, and lead off at K. Then we have two 
circuits connecting A with K, the first consisting of the two 
coils ( 1 ) and ( 2 ), the second of the coil ( 5 ) of the same length 
but of four times the cross section and going round in the 
opposite direction. Since the needle is not deflected the 
two currents exert equal forces. But the coil ( 5 ) is at twice 
the distance and must therefore 15 have four times as great a 
o 
current through it as that through (1) and (2). That is, 
with equal lengths of wire of the same material connecting 
two points the currents conveyed are proportional to the 
cross sections. 
“ On Aurin, Part II.,” by R. S. Dale, B. A., and C. Schor- 
lemmer, F.R.S. 
Some time ago we read a paper before this Society, in 
which we stated that, on heating aurin Ci 9 Hi 4 0 3 with an ex- 
cess of aqueous ammonia, it is converted into pararosaniline 
C19H17N3* There ought to exist two compounds, standing 
intermediate between aurin and rosaniline, viz., C 19 H 15 N 0 2 
and C 19 H 16 N 2 0 , as the action of ammonia probably proceeds 
in three stages : 
c 19 h 14 o 3 + nh 3 = c 19 h 16 no 2 + h 2 o 
C 19 H 15 N 0 2 + RH3 = C19H16R2Q + h 2 0 
C 19 H 1 g N 2 0 + NH 3 = OigH^Nij + H 2 0 
* Mem, Lit. Phil, Soc. (3) vi., 248. 
