of Magndic Induction in an Elongated Spheroid* 67 
the zero position, and ordinates the throws obtained at 
corresponding positions. 
I. In the final experiments the thin coil was moved up, a 
centimetre at a time, by means of a mechanical arrangement 
allowing of the actual displacement being read off on a 
vertical scale parallel to the axis of the rod. The following- 
table gives the results obtained after a slight correction on 
account of the direct action of the maorietizino- coil. 
Distance 
4 X throw. 
4 X throw. 
Men a 
Throw 
from zero. 
Exp. III. 
Exp. IV. 
throw. 
per cm. of rod. 

37 6 
36-7 
9-29 
1 
34-95 
33-55 
856 
•73 
o 
32-2 
3105 
7-9 
•66 
3 
- 29:5 
28-4 
7-22 
•68 
4 
26-6 
261 
6-59 
•63 
5 
24-1 
23-7 
597 
•62 
6 
21*4 
2135 
5-34 
•63 
7 
19-4 
19 25 
483 
•51 
8 
17-12 
17-16 
4-23 
•55 
9 
15-1 
14-8 
3-73 
•55 
10 
13 
128 
322 
•5L 
11 
10-73 
1063 
2-67 
55 
12 
8-9 
8-6 
219 
•48 
[In Exp. III. the exploring coil was moved from the zero position, and 
in Exp. IV. to the zero position.] 
The results are also plotted in the Curve II. It will be 
seen that both sets of experiments give practically identical 
results, viz., that the curve is straight with a slight upward 
trend for the first three cms. from the zero. In order to 
explain this, we note that the rod is not altogether spheroidal 
in form, but is practically a cylinder with a rounded off end, 
so that the small coil for the first few centimetres from the 
zero position embraces more lines of force than if the rod 
were accurately spheroidal. AVe conclude therefore that the 
formula (§ 1) is experimentally verified for an elongated 
spheroid. It will therefore be necessarily also true of a cylin- 
drical rod with rounded off ends, if the rod is sufficiently thin. 
5. Further it is seen that in the latter case the lines of force 
are radial and uniformly distributed. 
Moreover, if m be the total amount of induced magnetism 
over such a cylinder, 
4z7rm = B, 
and p=linear density of this magnetism, 
or 
4n$pd.T=B, 
dB 
-5— =p = coust. : 
cLv r 
F 2 
