454 E. L. Nichols—Character and Intensity of the 
field of sight. Images of two parts of the scale were brought 
by total reflections in the set of prisms into the field (see fig. 6), 
the portion lying between divisions 194 and 204, and overlapp- 
ing this the portion from division 64 to 65.’ Now turning the 
plates of the opthalmometer until the lines 20 and 64°5 coincided, 
which occurred when the angle was, according to three suc- 
cessive readings, 29°-12’, 29°-18’, 29°-12’, sufficed to show how 
much the distance m m, exceeded 44°5™™. 
From formula (6) we find, 
mm, = 44°55748™™, 
to which quantity it was only necessary to add for any state of 
the wire the directly obtainable value a, 4,, in order to know 
a, the length of the piece of wire in question. 
i 
S UO ie | tH 
Cold wire. Hot wire. 
fused upon the wire in the desired places. This plan served 
; _on the contrary, answered admirably. At the prope? 
points simple loops of exceedingly thin platinum vie e ee 
e latt 
the current, — 
Set 
mS pn seoe iat i ie 
Dyes» hy 
no ee 
