A shaft, connected by an arrangement of geared wheels to the drum, passes through the center of the segmented ring and carries a loose collar; a stout metal rod is firmly attached near its longitudinal center to this loose collar. One arm of the rod carries a laminated metal scraper, or contact brush, arranged to travel around the periphery of the ring, and in its revolution to make contact with each segment in succession. The contact brush is connected through the arm with one pole of the battery; and each segment—through its independent wire and magnet of the electro-exposors—with the other pole.
| Fig. 7. | Fig. 7. |
When twenty-four consecutive phases of an act of motion are to be photographed from one point of view, all of the insulated segments in the ring are put in circuit. When twelve consecutive phases are to be photographed synchronously from each of three points of view, each alternate segment is placed in circuit with the electric battery.
The manner in which the series of synchronous exposures is effected will be readily understood by reference to the diagram, 8.
All being in readiness, and the weights and fan wheel adjusted to cause the contact brush to sweep over the periphery of the ring at the required rate of speed, the drum, and with it the shaft is set in motion.
At the proper time, pressure on a button completes an independent circuit through the magnet seen below the segmented ring, figure 7, and in the side diagram of figure 8.
The action of the armature releases the lower end of the rod on the loose collar, which, by means of a coiled spring, is immediately thrown into gearing with the already revolving shaft; the contact brush sweeps around the segmented ring and effects the consecutive series of exposures at the pre-arranged intervals of time.
At the University the intervals varied from the one-sixtieth part of a second to several seconds.
A record of these time intervals was kept by a chronograph, a well known instrument; it comprises a revolving drum carrying a cylinder of smoke-blackened paper, on which, by means of successive electric contacts, a pencil is caused to record the vibrations of a tuning fork, while a second pencil marks the commencement of each photographic exposure. The number of vibrations occurring between any two successive exposures marks the time. The tuning fork used made one hundred single vibrations in a second of time. To ensure greater minuteness and accuracy in the record, the vibrations were divided into tenths, and the intervals calculated in thousandths of a second.