A. M. Mayer—Researches in Electro-Magnetism. 199 
affected in the same circumstances of magnetization), were insu- 
lated by dipping them separately into parafine, melted in a tube 
about 12 in. long, and were thus uniformly coated with a firm 
layer of that substance. They were then closely tied together 
into bundles by means of silken thread. The helices, in all the 
experiments on the cores, were placed 8 feet apart. 
To abbreviate the descriptions of the experiments we will always 
place the E helix east of the compass and the W helix west, 
and to indicate the deflection of the needle we will use such ex- 
pressions as “S. 17° W.” which means, 8S. end of needle deflect- 
ed 17° W. or toward helix W. In the case of N. poles facing 
the compass the above expression would show that the core of 
helix W was stronger than that of helix E. Ifthe current was 
reversed it would indicate that the EH helix was the stronger. 
When not otherwise stated it will be understood that the N. 
poles of the helices face the needle, and therefore the expression 
given of the deflection will always show which of the cores has 
the greater action on the needle. To designate the different 
wire-cores we will use “100 or 400 UC” or “100 or 400 IC,” 
which respectively mean, the uninsulated core of 100 or 400 wires 
and the insulated core of 100 or 400 wires. T. G. stands for t tan- 
gent ee 
mt 1. Helices alone, without cores. Needle placed 
midway heehee helices and brought to 0°. Current passed from 
10 Bunsen cells. Needle 8. 4° E. TT. G. 58°. 
Ex, 2. Reversed current 8. 4° W. T. G. 58°. 
Ez. 3. Moved needle toward W. helix so that it oye at 
the stronger. 
Ex. 4. Three cores of 400 wires each, one of insulated wires, 
were compressed to exactly the same diameter of 1°64 ins. An 
uninsulated core was placed in each helix, and the needle a 
- rts between the helices. Cenechi = S. 27° 
Ex. 5. Current reversed S. Ws 
Fz. 6. Other circumstances remaining as in a moved needle 
toward W helix until it stood at 0° when circuit was open or 
closed. Needle distant from E helix 55°6 in. 
Expt. repeated many times, with current direct and cael 
with the same result. 
Ex. 7. Intere the cores in the helices. Current t passed. 
Needle still at 0°. T. G. 48°. Current reversed. Needle at 0°. 
This shows fae the cores were sctktly affected in the same 
circumstance 
Ex. 8. Replaced I E core Bed heir insulated core of 400 ned 
wires. Ne having re in same position as in d 
(7), Current passed. “S. 66’ W. T. @. 48° “ 
