amount of energy spent upon the air is very great in this experiment and the coil in action produces the effect of a hot furnace, creating a strong current of air through the open roof which, rushing upward, takes effect upon the streamers as is plainly recorded on the plate, particularly on the upper streamers. A very interesting long spark passes to the wire leading from the secondary. It is evident that many streamers are split up to such an extent that they do not impress the film sufficiently. In the experiment also 100 throws of the switch were made and the other particulars were nearly the same as before. The e.m.f. at the terminals of the extra coil system is necessarily smaller because of the facility afforded for the escape of the streamers and great frictional loss in the air, which causes the free oscillations of the system to die out more quickly than in some of the foregoing experiments.
L. This photograph represents a similar view of the extra coil discharging from the brass ring and wires fastened to same; in this case the wires being directed downwards. The streamers show much the same character as before and many are evidently not strong enough to record their path on the film, on account of the great quantity of them. Most of them produce the effect of a strong glow only. Some strong sparks pass occasionally to the wire leading from the secondary. Again, the photograph was produced by 100 closures of the switch and normal excitation of the extra coil system.
LI. This is once more the extra coil discharging under similar conditions and viewed in the same manner. The wires fastened to the brass ring forming the last turn of extra coil are in this case pointed still more downwards. To strengthen the streamers somewhat the number of the discharging wires is reduced. The streamers on the top part of the picture are very beautiful, their paths being curiously curved. But the fine texture of the discharge again shows the weakening effect of the many wires or points of issue, though the individual discharges are evidently stronger than before. Some sparks passing to the hood and floor are interesting and show that the e.m.f. has been increased by reducing the number of the discharging wires. In fact some sparks and streamers attain great length and there are a number of instances of their splitting up in curious ways illustrated. A strong draught effect is also apparent. The photograph is rendered more beautiful by its symmetry. All particulars remained as before.
Colorado Springs
Jan. 6, 1900
Photographs taken with Mr. Alley from Dec. 17 to Dec. 31, 1899 and particulars relating to the same continued:
LII. This plate shows a discharge from the top of the extra coil, produced by a single closure of the circuit or throw of the switch, of very short duration. The discharge issues again from the brass ring on the top of the extra coil, which is viewed centrally. Some streamers pass into the air and sparks dart to the hood above the coil. A curious spiral or screw motion in one or two streamers is noticeable. The light of the discharge, though lasting but one fraction of a second, is strong enough to reveal a part of the structure and the top of the coil. The current of air separates the sparks and streamers into the individual discharges produced by the break wheel. This effect is beautifully shown. The vibra-
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