10. A cylinder of agglomerate of zinc powder in paraffin, with 40 per cent. of zinc.
11. A cylinder of brass filings in paraffin, 20 per cent. of metal.
12. A tube of glass, 4·5 centimetres diameter, filled with various electrolytes.
Fig. 67.
The manner of observing was as follows (the experiments were done in the laboratory of Hertz):—
The resonator, with its spiral empty, was syntonised with the exciter, and the maximum spark measured. It was between 4 and 9 millimetres long in these experiments. Then one or other of the above cylinders was introduced and the spark length measured afresh.
Cylinder 1 did not affect the maximum spark length. Cylinders 2-4 reduced the maximum spark to ⅒th of its former value; 7 and 8 to ¹/₁₀₀th, and No. 9 to ¹/₂₀₀th of its former value (viz., from 9 millimetres to ·05 millimetre). Nos. 10 and 11 had but a feeble action, and reduced the spark from 8 to 7 millimetres.
Tube No. 12, filled with distilled water, scarcely affected the spark length; the period of the secondary increases a little, but the maximum spark is the same as before, once syntony is re-established. Filled, however, with dilute sulphuric acid, containing 10, 20, or 30 per cent., the tube reduced the spark considerably, in each case about the same, viz., from 9 to 1·3 about. (Currents induced by Maxwellian radiation in electrolytes had been already observed by J. J. Thomson.)
While trying to re-establish syntony between primary and secondary, I found that the period of the resonator was considerably increased by the cylinders 2-4, but that the maximum spark length was much diminished. With the cylinders Nos. 5-9 in the spiral, it was no longer possible to establish syntony, “a fact which is certainly due to their considerable absorption of energy. Take, for example, cylinder 9: electromagnetic energy must converge rapidly towards it in order to be transformed, and the space finds itself empty of energy as air is exhausted of vapour in presence of an absorbing substance.”