The name sciascope was early suggested by Prof. Magie. For those who wish to make a screen, the author may state that he obtained a good one by mixing pulverized barium platino cyanide with varnish and spreading the mixture over a sheet of tracing cloth. ------------------------------------------------------------------------ CHAPTER VIII ------- [Illustration] 97_a_. HERTZ’ EXPERIMENTS. ELECTRIFIED BODIES DISCHARGED BY ULTRA-VIOLET LIGHT OF A SPARK AND BY OTHER SOURCES OF LIGHT. _Berlin Akad._ II., p. 487, ’87. _Wied Ann._ XXXI, p. 983. English translation of the above. Lon. and N.Y. Macmillan, p. 63, ’93. From notes by Mr. N. D. C. Hodges.—This is the all-important initial work of H. Hertz. The source of light was a spark, and the great discovery resulted from a combination of circumstances and was unsought; but by studying and testing the matter, he found the cause. Two induction coils, _a_ and _b_, having interrupter _d_, were included in the same circuit, as shown in the figure. The sparking of the active one (A) increased the length of the spark of the passive (B) § 10. He sought the cause. The discharge was more marked as the distance between the sparks was reduced. Sparks between the knobs had the same effect as those between points; but the effect was best displayed when the spark B was between knobs. The relation between the two sparks was reciprocal. The discharging effect of the active spark (A) spread out on all sides, according to the laws of light, first suggesting that light was the cause. Most solid bodies acted as screens, s. Liquid and gases served more or less as screens. The intensity of the action increased by the rarefaction of the air around the passive spark, __i.e.__, in a discharge tube. The radiations from the spark, A, reflected from most surfaces, according to the laws of light, and refracted according to the same laws, caused the discharge. The ultra-violet light of the spark A was inferred to be the active agent in producing the discharge. The same effect was produced by other sources of light than the electric spark. The conclusions were afterwards confirmed by many, and subordinate discoveries originated. § 98—99T.