MECHANICAL CONNEXION BETWEEN ETHER AND I^IATTER. 
155 
shaking, but as the speed increased they became clear, and at 800 revolutions were 
quite sharp. At 1000 revolutions per minute a careful set of observations was made, 
with the magnetising current applied to the spheroid,—on, off, reverse, oft*—many 
times. But there was no effect whatever on the bands. Then we slackened speed 
and repeated the magnetisation and reversals down to stoppage, but not a trace of 
shift. The flickering and blurring of the bands, already spoken of, which still occurred 
at low speeds, and especially at increasing speeds, was not a serious trouble. It of 
course prevented exact observation while it occurred, but it was a purely temporary 
disturbance and did not cause the slightest permanent shift. As soon as the bands 
were clear again their position was absolutely unchanged. Nevertheless it was 
desirable to detect and remove the cause of the disturbance. Accordingly air was 
blown into the channel from foot bellows, but unless the wire coil inside had been 
recently used and imperceptibly warmed by the current the air jet made very little 
difference, though if there was the slightest inequality of temperature it caused a 
slight flicker. But a whiff of coal gas, the merest trace, distorted the bands with 
agony—sent them waving through ellipses and contortions into invisibility, allowing 
them to re-appear as the gas diffused away. They were manifestly extremely sensi¬ 
tive to fluctuating density, and hence we traced the previous flicker to hot air from 
the carbon rheostat which regulated the driving current. It seemed to get drawn 
into the channel sometimes at low sjDeeds, but at high speeds was blown clear away. 
Starti]ig and stopping tire iron by hand did not cause the bands to flicker; they only 
flickered when the motor was used. It was plainly a heat convection effect. Hence 
we arranged that the carbon rheostat should be far away, and even the slight heat of 
the motor itself was screened and diverted off by a suitable platform or tray of wood 
and cardboard arranged above the motor. 
T 
Now I repeated the observations over and over again, with all sorts of changes, and 
never found either motion or magnetisation of the heavy iron mass cause the slightest 
real shift of the bands at the speed of 1000. 
The channel being narrow, the plates themselves were visible in the eye-piece, and 
the bands could be seen reflected in them. Also diffraction or interference phenomena 
could be seen where the bands terminated on the iron (Lloyd’s bands due to oblique 
reflexion) at one or other of the plates. A frequent appearance of the bands under 
these circumstances is depicted in fig. 3, next page. 
These reflected bands, and also the horizontal houndary stripes with the swellings 
of the bands on them, were also watched, the cross wires being shifted and set 
upon one feature after another, but in no case was the slightest shift seen on 
magnetisation; though certainly the test was not so delicate as with the free-air 
bands, because the plane of the channel-boundaries was not absolutely steady as the 
plates revolved. 
The bands observed were often so broad that the distance between them was 
comparable with the half-inch channel-width, nnd sometimes the cross of the hyper- 
X 2 
