Table III., showing orchestral pitches obtained in 1899, for the measurements of which the writer is responsible, prove how chimerical it is to hope for greater accuracy than is found between 435 and 440 vibrations a second for a', inasmuch as temperature must always be reckoned with.
The condenser method of making oscillations is analogous to the production of air vibrations by twanging a harp string at short intervals.
Both Bell and Gray proposed to do this by introducing a column of liquid into the circuit, the length or the resistance of which could be varied by causing the vibrations of the diaphragm to vary the depth of immersion of a light rod fixed to it and dipping into the liquid.
When the compass is far from the magnet, the vibrations will be comparatively slow; when it is near a pole, they will be exceedingly rapid, the frequency of the vibrations varying as the square root of the magnetic force at the spot.
According to the best determinations the value of elm does not exceed 1.8X Io', and T is of the order of Io 15 second, the period of luminous vibrations; hence OM/M must always be less than 109 H, and therefore the strongest fields yet reached experimentally, which fall considerably short of Io %, could not change the magnetic moment M by as much as a ten-thousandth part.