The Earliest Electromagnetic Instruments — John Shaqi
The Earliest Electromagnetic InstrumentsChipman, Robert A.
History
The Earliest Electromagnetic Instruments
Chipman, Robert A.
Electric apparatus and appliances
To instruct myself on this point I made use of three separate
circuits, each containing an 8-turn condenser, and put these as
close together as possible in the magnetic meridian ... with the
needle between the windings. Each single circuit ... gave a
deflection of 45 deg. ... When two were connected the deflection was
60 deg., and when finally all three were put in magnetic operation, the
deflection grew to only 70 deg. It appears clearly from this that the
angle of deflection is not in a simple ratio with the magnetic force
acting on the needle....
Neither Poggendorf nor Schweigger seems to have ruled out, on logical
grounds alone, the possibility of deflections greater than 90 deg., with
the loop-plane in the magnetic meridian, though Poggendorf does add a vague
note that if the needle deflected too far it would encounter forces of
the opposing sign.
Poggendorf experimented with the size of the circuit wires, finding that
larger wires led to greater deflections. He noted that the size of the
cell plates and the nature of the cell's moist conductors would
certainly have a great effect, but that to investigate these in detail
would take undue time, and he therefore proposed to keep this part of
the apparatus constant, using one pair of zinc and copper plates 3.6
inches in diameter, separated by cloth soaked in ammonium-chloride
solution.
Poggendorf's principal quantitative study of his magnetic condenser used
13 identical coils, each with 100 turns. In order that the turns should
all be at approximately the same distance from the needle, the coils
were wound of the finest brass wire that could be silk-insulated, the
wire diameter being 0.02 lines. On adding coils one at a time across the
cell (i.e., connecting them in parallel), the deflections were as
follows:
Turns 100 200 300 400 500 600 700
Deflection in
degrees 45 50 55 59-60 62 63 64
Turns 800 900 1000 1100 1200 1300
Deflection in
degrees 65 65-1/2 66 66 66 66
Adding some coils with fewer turns, and connecting various combinations
"as a _continuum_" (i.e., in series), the deflections using the same
cell were:
Turns 1 5 10 25 50 75 100 200
Deflection in
degrees 10 22 27 30 35-40 40 40 40
Turns 300 400 500 600 700 800 900 1000
Deflection in
degrees 40 40 41 40 40 40 40 40
Making a few coils from wire with 1/8-line diameter, the deflections,
again using the same cell were:
Turns 5 25 50 100 Over 100
Deflection in degrees 20-22 40-45 45 65 65
Public-domain text, read in full here on John Shaqi.
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