Oliver Lodge

“ And although radiation is not any known kind of mechanical disturbance, but is concerned with the ether's electrical properties, end need not necessarily involve anything analogous to etherial viscosity even in the neighbourhood of matter, yet it was thought possible that electric charge, being as it were the connexion between ether and matter, might confer upon a material body some power of gripping and rotationally carrying forward the ether in a quasi-viscous manner. ”

“ The connexion looked for between ether and matter being something of the nature of viscosity, the space between the disks may be considered rather wide; though it is difficult to suppose that any motion generated at the surface of the disks in a substance possessing any of the properties of an ordinary fluid, should not spread into the nearly enclosed space between them. ”

“ It is to be observed, that since a motion of the disks relatively to the observer and the light causes no effect, the ether being stationary, it follows that a motion of the light and observer would produce an effect, since they would be moving relatively to the ether. Hence if, instead of spinning only the disks, the whole apparatus, lantern, optical frame, telescope, observer and all were mounted on a turntable and caused to rotate, a reversible shift of the bands should be seen. ”

“ If the ether is stationary near the earth, that is, if it be neither carried round nor along by that body, then a single interference square, 1 kilometre in the side, would show a shift of rather more than one band width, due to the earth’s rotation in these latitudes ”

“ In an actual experiment of this kind, centrifugal force would give some trouble by introducing strains, and rapid rotation would be uncomfortable for the observer; but really rapid rotation should be unnecessary to show the effect. My present optical apparatus mounted on a turn-table revolving 4 times a minute should show something, viz.: th band shift each way. A certain amount of discomfort during the accelerative stages of any speed could hardly be avoided, and even during steady motion there would be some inconvenience ”

“ With this plan, alternate light paths go between the disks, and accordingly the density-gradient-effect, if any, is uncompensated. A very narrow beam was used, however, and the effect is demonstrably small, though it probably accounts for the irreversible shift observed.
There was not a wink when the sparks occurred, whatever the speed. The test for electricification effect is easy, because the charge can be switched on and off while in a state of steady spin, and the slightest difference would be observed. There is certainly no perceptible effect. ”

“ The dots represent individual settings and readings of the micrometer cross wire set on the middle band during a pair of spins in opposite directions, while the speed was first increasing and then decreasing.
Corresponding concertina action (on same scale) , or change in the breadth of the bands during the above spurious shift. Dots represent differences between the readings of a micrometer wire set on the yellow of the 1st order and the readings of the cross wire set on the middle band. The zero of the vertical scale is far below, 7 squares below 0. ”

“ There was a trace of irreversible shift when the disks were spinning, but its amount was quite independent of the direction of rotation, and there was not the slightest difference whether the plates were electrified or not.
The path of light in this set of experiments was the long oblong with two of its sides between the disks as already briefly mentioned. The mirrors were supported on opposite wells of the room, and a diagram of the arrangement is annexed (fig. 8) , the light being sent three or more times round the oblong. ”

“ The bands were distinct all the time. A good experiment. We conclude that time has nothing to do with the matter.
Attempt to Observe the Air Efect.
From June to November, 1893, continual attempts were made (except during a month's vacation) , by careful and repeated setting of the micrometer wires on the bands, by taking the average of a set of readings at each speed and plotting them, to get some dependable record of the true air effect, free from disturbing causes. ”

“ Ultimately we decided to do away with the optical frame so close to the disks altogether, and to arrange the mirrors at a distance, out of the blast, on brackets fixed to opposite walls of the room, sending the light round a large oblong instead of a square, and letting two sides of this oblong pass through the channel between the disks. (The arrangement of this experiment is shown in fig. 8.) Meanwhile, we dismantled the machine and sent the disks back to Mather & Platt to be fitted with a third one for electrification. ”

“ The machine now ran up to 2400 without a tremor, and a current of 30 to 35 amperes was sufficient to do the driving. An observation was made with the drum in, with glazed windows, no top or bottom (as before) , the light going three times round, and the speed being kept at 2100 for two hours. At the first instant there was a shift of th band, but it did not increase, nor did it recover on stopping. Went on with a reverse spin, also at 2100, under the same conditions, and saw not a trace of shift at going or stopping, or during long spin — only the usual flicker as the speed got very slow. ”

“ 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 considerable magnitude; but if by any accident the force transmitted was too great, the wires could snap and permit independent movement of the mass. ”

“ These disks had been spun, at a speed not exceeding 1250 revolutions a minute in the most accurate experiments, and the effect of the motion on a bifurcated beam of light, whose two halves travelled in opposite directions several times round in the space between the disks, was observed. One half of the light travelled in the same sense as the motion, while the other half travelled in the opposite sense ”

“ The shift observed now was moderately small but quite distinct, and was estimated with the micrometer at th band. It repeated itself each time without regard to the direction of spin, and disappeared, though not instantly, when the disks stopped. It seemed probably due to some obscure residual effect of the blast, perhaps on the cover glasses of the drum. The shift was irreversible, and of reversible shift there was none.
At these higher speeds it would naturally be thought that the true theoretical effect due to whirling air () should be observable ”

“ Taking for air as 1.00029, the , and the fraction of a band shift observed being at an angular speed , and with light-journeys round the optical square of side , we should have (see p. 772, loc. cit.) ; wherefore, writing , and considering that the observable is th of a band, it follows N must be 300, in order to show the air effect, that is, the speed must rise to 6000 revolutions a minute with a light-journey of three times round. This speed would lead impractically near to the bursting-strength of materials ”

“ Hence, for disks a yard in diameter making 3000 revolutions a minute, the density at centre is about 8/9ths of that at circumference; and the change of density per centimetre breadth of beam, at a radius of 1 foot, is
which, if be taken as proportional to , gives about equal to .23 ”