Rays emitted by Glowing Platinum. 455 
small wire, fine as a fiber of raw silk, and scarcely visible to 
the naked eye, melted on touching the hot metal and became 
fixed upon its surface. The whole, seen through the micro- 
desired accuracy. The opthalmometer is free from many errors 
which by cathetometric and micrometric measurements are 
unavoidab] 
; 
the platinum suffered a change of condition. not melt; 
but the wire lost its stiffness, hung down limp, scarcely holding 
together, and quivered when jarred like jelly nder these 
circumstances measurements became unreliable very 
weakest place. The conducting power being thus diminished, 
the temperature would rise very rapidly until after glowing 
brilliantly for a moment, the platinum would melt and the 
wire break. 
: g : 
investigation. The opthalmometer also, having been placed in 
the position most advantageous for the measurement of the 
expansion of the platinum wire, remained undisturbed through- 
out all the experiments. The leucoscope was set up two meters 
distant from the two wires. 
lvanic circuits of which the wires formed a part 
wire be made to 
, th suffices to move “PH 
center considerably from its original position. To avoid disturbance from this 
cause I serge gare ath 8 inse e lower ends into short 
Th 
of mercury. To prevent heating, | 
