240 Intelligence and Miscellaneous Articles. 
gutta-percha, and with paper of different thicknesses; but find 
tissue-paper varnished and used double, according to Mr. Bentley’s 
plan, the best. The surfaces used in the instruments above described 
are respectively about 30 and 75 square feet. I have used all the 
interruptors alluded to by the writers above mentioned, but prefer 
one which I have made thus :—The anvil is a wire or small rod of 
platinum secured in a plate by a binding-screw; over this a rod of 
platinum is secured in the same manner to a spring which presses 
them together; another spring loaded acts like a hammer upon the 
end of the first spring, to separate the platinum rods. A ratchet- 
wheel presses down this spring-hammer, and allows it to recoil and 
strike the other spring. By this the interruption is more instanta- 
neously made, and the distance to which the platinum rods are sepa- 
rated easily regulated. This point appears to be of importance. 
The spark is lessened if the platinum rods are separated further than 
actually to break their contact. The usual primary helix of large 
wire and the interior bundle of iron wires are placed within the glass 
tube. 
In my last instrument, I used a tube closed at the top, more effect- 
ually to cut off the passage of the current from one end to the other 
through the primary helix or iron wires. I have used a Bunsen’s 
battery of four to six cells; four give the spark of as great length, 
but a few more cells increase the volume. I have applied a battery 
of eighteen cells, and also a plate battery of fifty-six pairs, without 
endangering the coil. The instrument is undoubtedly capable of 
being greatly increased in size and power. 
Boston, May 2, 1857. 
P.S. Since writing my paper, I have constructed a helix in which 
the plane of the strata of wires is perpendicular to the tube, insulated 
as before. With one of the same length of wire as the largest one 
before mentioned,—throwing a spark, with six cells, 6 inches,—I 
have used a battery of eighteen cells (Bunsen’s); but by using a 
battery of three series of six cells (that is, an intensity of six, and 
quantity of three), a very voluminous spark was obtained; as the 
action soon became feeble, I took the secondary coil from the glass 
cylinder and found that the current had passed through the glass near 
each end of the coil, forming a circuit through the primary wire ; 
two minute holes, of a hair’s breadth, from one-tenth to one-eighth 
of an inch in diameter, were drilled through, but the giass was not 
Fractured; it also passed through several thicknesses of vulcanized 
india-rubber. The helix was uninjured, proving the insulation ob- 
tained by the mode of winding it. A more perfect insulation between 
the helices is readily made ; and I now use a tube of gutta-percha over 
the glass. With powerful batteries the condenser of varnished paper 
is not sufficient, as the current passes entirely through, and with 
such I use oiled silk, I have put several condensers in the same 
instrument, connecting each by turning a screw, so that either or 
all can be used. Varied and beautiful effects are produced, particu- 
larly in vacuo, by using different amounts of surface of condenser.— 
June 10, 1857. Fyrom Silliman’s American Journal for July 1857. 
Pee ae ren & 
