LINES OF MAGNETIC FORCE — WIRES OF DIFFERENT SUBSTANCES. 
47 
lead, platinum, zinc. Under these circumstances the substance concerned in the ex- 
citement of the current is made to vary, whilst the conducting part of the system is 
very good and remains the same. The results with these loops were as follows, being 
the average of from six to ten experiments for each loop : — 
Copper 63‘0 
Silver 6 T9 
Zinc 3T5 
Tin 19-1 
Iron 18‘0 
Platinum 16‘9 
Lead 12T 
3146. In order to dismiss, as much as possible, the obstruction caused by bad con- 
ducting power, and bring out any difference that might exist between paramagnetic 
and diamagnetic metals, three metals were selected, namely, tin, iron and lead in 
wires, as before, of 0‘04 of an inch diameter ; but the length was restricted to 3 inches, 
instead of extending to 10’5 inches, and the rest of the loop was made up of the con- 
ducting copper wire of 0*2 in diameter, as in fig. 18. 
Of course, the effect of the whole loop is a mixed 
effect, being partly due to the power represented 
by the lines intersected by the thick copper por- 
tion, and partly by those intersected by the three inches of special wire passing 
between the poles. But as the great amount of force is concentrated within a 
space not more than an inch and a half or 2 inches in extent (as is seen on carrying 
any of the loops across the magnetic axis), and as even that could be made still more 
concentrated by using the iron cube (3129.), and so bringing the poles virtually 
nearer to each other, it was hoped that the chief effect would be there, and so any 
peculiar difference existing between iron on the one hand and tin and lead on the 
other, be rendered manifest, especially as the resistance to conduction was greatly 
diminished by shortening the wires from 10’5 to 3 inches. 
3147. The many experiments made with each metal were very close together. 
The average of the results for the three metals was as follows ; — 
Tin 
.... 371 
Iron 
.... 34-8 
Lead 
25-4 
The proportions, and therefore the results, are almost identical with those obtained 
before (3145.). 
3148. When lead and copper, arranged at the bar magnets (3084. 3085.), had been 
compared in former experiments with each other by the fine wire galvanometer, the 
results for both had been the same. But then the two wires used were short, and 
Fig. 18 . 
