154 
PROFESSOR OLIVER LODGE ON THE ABSENCE OF 
chamber) had insufficient area ; the intensity of pressure was too great for lubrica¬ 
tion, and accordingly the surfaces ground together and got hot, causing the oil vessel 
to smoke vigorously. Considerable power was, therefore, needed to drive it, even at 
300 revolutions a minute, but at this speed some observations were made. The bands 
were so clear that yoof^ ^ band shift, could have been seen, but there was not a 
trace of shift when the mass was spinning, either with or without its magnetising 
current. The 110 volts of the town main were switched on and off and reversed 
many times, both when the mass was stationary and when it was revolving five 
times a second, but there was no effect. 
Before proceeding to greater speeds it was obvious that the greater part of the 
weight of the iron mass must 1)e taken off the pivot and dynamo-axle, and must be 
supported in some other way.. A safety collar or guard attached to a frame above 
the wooden clutch, as shown in Plate 32, ‘ Phil. Trans.,’ A, 1893, suggested the use 
of ball-bearings resting on this collar, which hitherto had been an inactive safety- 
guard, but was quite strong enough to support the weight required. 
Accordingly we had this arrangement made, all the weight of the spheroid now 
rested on the guard collar by means of ball-bearings, and the steel pivot had nothing 
but the dynamo armature to support, this axle also being quite relieved from strain. 
The old wooden friction clutch was now of course useless, and it was replaced by gripping 
brass collars on the ends of the joining shafts, just below the ball-bearings, the power 
being transmitted by a pair of tangential stout copper wires, one on each side, looped 
round screw heads on the brass collars, so as to transmit a driving couple of consider¬ 
able magnitude; but if by any accident the force transmitted was too great, the 
wires could snap and permit independent movement of the mass. Parenthetically it 
may be here stated that the wires broke several times during the course of the series 
of experiments, showing that the precaution was very necessary, and that a rigid con¬ 
nexion between the axles would have been dangerous. 
During these alterations, other experiments, to be presently recorded, were in 
progress, and it was not till May, 1893, that careful optical spins were again conducted 
with the iron spheroid. 
At this date the fringes were sometimes used after the light had been four or five 
times round, but usually the superior brightness and definition of the three-times- 
round beam was preferred. With a driving current of from 30 to 40 amperes and a 
voltage of about 80, the speed of 1000 a minute was readily maintained in the heavy 
mass by aid of the ball-bearings. 
At first, however, a new disturbing phenomenon was observed : on beginning a 
spin the bands began to tremble and became partially obscure. This was not from 
shaking, nor did it seem likely to be due to wind reaching the semi-transparent 
plate, because the speed was quite slow. Screens glazed with microscope cover-glass 
were nevertheless provided, and next day another attempt was made. The fiickering 
of the bands was just the same as before at low speeds, although there was no 
