was used as the feature upon which the cross wires were set, so that an exceedingly small fraction of a band-width could have been observed.
At 1000 revolutions a minute, the ball-bearings began to get hot, and some attention had to be paid to them to get the number of steel shot and the lubrication as perfect as possible. The iron mass took a long time to slow down from full speed, and after being left to itself for twenty minutes or half an hour was still moving. Sometimes it was stopped more quickly by a brake, to me if acceleration had any effect, but none was seen.
On the 8th May, 1893, we had a good spin at 1200 a minute with the spheroid,
magnetisad and reversed, etc., looking as carefully as possible at the bands reflected in the iron and at every part of the bands, but no change of the minutest kind was visible.
On the 9th May, we had a similar spin in the reverse direction, conditions fairly, satisfactory, and results definitely negative.
Sometimes an alternating or cummutated current was supplied to the coil, but its self-inductance and time-constant were so great that little power could be thus developed. Anyhow, no shift of the bands was seen.
Experiments at Higher Speeds.
During the next few weeks, the iron spheroid was replaced by the old steel disks, and great pains were bestowed on getting these accurately balanced, so that a high speed could be reached without tremor.
By June, the ether machine could be driven at speeds above 3000 a minute, the power used being 50 amperes and 100 volts.
But at these higher speeds there were many difficulties. The blast was, of course, excessively strong, and it was necessary to carefully screen it from the mirrors and frame by boxing the plates up in the wooden drum before described; moreover, higher speeds could be attained with the air thus boxed up. But the air got very
