200 A. M. Mayer—Researches in Electro-Magnetism. 
Fx. 9. Current reversed S. 55’ KE. T. G. 46°. 
Expts. 8 and 9 repeated several times with same results, show- 
ing that the insulated core was the weaker. 
Fx. 10. Moved needle toward E helix, which contained the 
400 insulated wires, until it stood at 0° when circuit was open 
or closed. In this position needle was 55-4 in. from E helix 
_The 100 wire-cores substituted for the 400 wire-cores gave 
same bundle of wires the following experiment was made. 
Fx. 11. The two cores of 400 LESS wires of 1°64 in. 
diameter were placed in the helices and needle brought so that 
it Bee 2 at 0° when cireuit was open or closed. The E core was 
now s my compressed that its diameter was reduced to 1°48, 
a replace in E helix, otherwise the circumstances were the 
5 
orce. 
It will be observed, in the above comparative experiment, 
that the two uninsulated wire-cores were of exactly the same 
strength when equally magnetized, (Ex. 7.) and that one of them 
remained in the W helix as unit of comparison to the uninsu- 
stands in the place of the “ unit-candle” in Bunsen’s method of 
hotometry, and the needle which is moved to such a position 
betes the helix that it remains at 0° when the circuit is open 
or closed is the equivalent of the paper screen with its central 
translucent circle. But if it should happen that when the needle 
is placed midway between two similar helices that it remains 
at 0° when the i is open or closed, then two cores wo 
answer the purpos 
— Calculation of be relative forces of the uninsulated and insulated 
cores.—The data for the calculation are given in Experiments 6 
and 10. 
W.UC: E.UC:: 40-4°™ : 55-6*™ : 1 : 2-39995. 
WUC: BIC 2: 40° (65a: 7 oye 
Hence Uninsulated Core: Insulated Core ::1-:0-9768. 
The insulated core is therefore 02318 ae than the unin- 
Jat 
In Expts. 8 and 9 it was seen that the above difference of 
‘02318 in magnetic force caused a deflection of 55’ in the com- 
