86 Prof. J. J. Thomson and Mr H. F. Newall,  [Feb. 28, 
cm. of its length, and currents of between 5 and 3°5 amperes were 
passed through it, so that we dealt with magnetizing forces of 
between 88 and 616 c. G.s. units. 
Lengths were cut from a round rod of soft iron of 12°7 mm. 
diameter, and were carefully softened. One length was 10cms., 
two others were 5 cms., so that these two put end to end made up 
a single length equal to the uncut -piece of 10 cms. We shall 
speak of the single one as the continuous core, the two 5 cms. 
pieces as the cut core. 
To measure the induction when these cores were put into the 
middle of the magnetizing coil, two turns of insulated wire were 
put round the core, and the ends connected as before with the 
‘ballistic galvanometer. For the cut core the wire was wound as 
near to the end of one of the halves as could be managed, and it 
was tied in this position, as it was found that a slight shifting of 
these wires along the length of the core produced considerable 
effects on the inductions. The position we have given to the 
turns of wire, which we shall speak of as the induction coil, will 
always give higher results than if the induction coil had been set 
midway between the cut ends: so that the reductions in the 
induction are always understated in the results we give in the fol- 
lowing Table I. 
TABLE I. 
Cores 1:27 cm. diam. 10 ems. long. 
Magnetizing force due to coil (47y) ... wis sch 200 280 460 
Induction. 
Continuous core ... die Bi ae uae ... | 6,048 | 8,400 | 14,160 
Cut core, worked ends (turned in a lathe) touching... | 5,472 
» 9» ends (worked on oilstone) touching ais 6,000 8,352 13,920 
» » ends separated by +127 mm. or 74, diam. | 5,328 | 7,296 | 12,432 
12 13 12 
dpe = a6 3 90 2x +127 mm. or ;2, diam. | 4,800 | 6,624 | 11,136 
21 21 21 
” ” ” ” 3 x +127 mm. or yay diam. 4,416 
27 Bae ihe 
Sree 4 dp 4-127 mm. or ;4, diam. | 4,032 | 5,568 9,504 
33 34 33 
” ” ” ” Sarin diam. 2, 352 3,264 
61 61 
Idiam. | 1,344 | 1,824 
78 78 
The numbers following the induction measures denote the per- 
centage reduction due to separation. The magnetizing forces here 
used are not such as to ‘saturate’ the cores, though there are signs 
of near approach of this. 
