628 Dr. KE. P. Harrison on the Temperature- Variation 
The wire was mounted in the fol- 
lowing manner :— 
On a solid base-board of mahogany 
A, fig. 1 (55 cms. long by 30 ems. 
wide by 3°5 cms. thick) was cut a 
groove (1'5 cm. deep by 1:8 cm. wide) 
which extended the whole length of 
the board. Thick brass plates H, F 
were screwed to the board in such 
a way as to close up the ends of 
the groove, and the nickel was then 
mounted so as to lie centrally therein. 
To effect this, one end of the wire 
was firmly clamped to a brass boss 
on the plate H, while the other 
end was attached to a brass disk D 
which was pressed outwards by the 
spring 8. The spring was kept in 
position by a tube T rigidly attached 
to the end-plate, while D was steadied 
by being soldered to another brass tube 
K which just slid inside T. The spring 
served the double purpose of keeping 
the wire under slight tension and of 
taking up the slack due to expansion. 
The tension on the wire could be 
regulated by adjusting a circular brass 
plate M which worked an a screw- 
thread cut on the tube T; by screwing 
M outwards or inwards the spring 
could be either compressed or relaxed, 
and the tension on the wire increased or 
reduced. ‘The tension used throughout 
these experiments was just enough to 
keep the wire straight. 
Binding-screws at B,; and B, allowed 
the nickel to be placed in circuit with 
the heating current. 
Two fine scratches g and q’ (fig. 1) 
about 10 cms. apart were made on the 
wire ; and it was the expansion of this 
portion gq’ that was observed. 
At t and ¢’ fine platinum wires were 
silver-soldered to the nickel for the 
purpose of measuring the resistance 
of the experimental portion ¢ ¢’ of the 
wire. ‘The distances gt, g’t’ were each 4°5 cms.; and thus as 
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