im changing the Dimensions of Iron. 171 
tube, which was then filled up with water. The stopper was 
then adjusted, and the capillary tube inserted so as to force the 
water to a convenient height within it. : 
“The bulk of the iron was about 4,500,000 times the capacity 
of each division of the graduated tube; consequently a very 
minute expansion of the former would have produced a very 
perceptible motion of the water in the capillary tube; but, on 
connecting the coil with a Daniell’s battery of five or six cells 
(a voltaic apparatus quite adequate to saturate the iron), no 
with the battery ; 
“Having thus ascertained that the bulk of the bar was in- 
variable, I proceeded to repeat my first experiments with a 
more delicate apparatus, in order, by a more careful investiga- 
tion of the laws of the increment of length, to ascend to the 
probable cause of the phenomenon. : 
“A coiled glass tube, similar to that already described, was 
Consequently, each division of the micrometer passed ey 
the index indicated an increment of the length of the bar 
amounting to ras377th of an inch. 
a circle of thick copper wire one foot in diat d 
needle half an inch long furnished with a suitable in sens to the 
on . ie quantities of magnetic polarity communica 
on 
