A. M. Mayer—Researches in Electro-Magnetism. 211 
and the effects of a combination of spirals composed of an equal 
number of turns of wire as the helix and existing in the same 
ength. 
Fifty spirals, each composed of 14 ft. 8-06 ins. of ,4; inch wire 
gave a “pitch” to the turns of the helix of 18 ins. and the 
innermost turns of the helix formed an angle of 1° 57’-25, and 
the outside turns formed an angle of 50’5 with the axis of the 
helix, alternately to the right and to the left, as it was wrapped. 
Each layer of turns of wire and twine was carefully saturated 
with melted parafine of a high temperature, so that the copper 
Mes iar through the saturated covering after the parafine had 
solidifie 
49 
openings a little sinter Chiat those of the spirals. This arrange- 
ment, as Prof. Joseph Henry has shown, so effectually cut of 
the mutual inductive action of the spirals that, on passing a 
current through them and breaking a mercury contact, the spark 
of the “ extra-current ” was (on account of the greater resistance 
of the spirals) less than when only the circuit of the battery 
wires was similarly broken. With the exception of the inte 
posed copper discs things remained as in Exp. 33. Current 
passed. eedle remained at 0°. Showing that the inductive 
