Decembee 11, 1896.] 



SCIENCE. 



855 



ing the pheuomenon was found to be by the 

 use of two induction coils, whose primary 

 circuits were placed in series with the same 

 interrupter. During most of Hertz's ob- 

 servations the distance between the two 

 coils was about 50 cm. The larger or * ac- 

 tive ' spark was about 1 cm. long, while the 

 length of the smaller or ' passive ' spark was 

 not far from 1 mm. Although especial at- 

 tention was directed to the influence of the 

 larger spark upon the smaller, it was proved 

 conclusively that the action was reciprocal. 

 The maximum sparking distance of each 

 spark was increased by the presence of the 

 other. 



4. Making use of this apparatus Hertz 

 investigated first the influence of changes 

 in the chai-acter of the active spark, and 

 found that the effectiveness of the latter 

 was independent of its form. The spark 

 could take place between spheres, or be- 

 tween points ; could be short and straight, 

 or long and zigzag ; could be brilliantly 

 wliite, or violet and almost invisible. In 

 all cases its action upon the passive spark 

 was practically the same. By screening 

 successivel}'^ different parts of the spark gap, 

 it was shown that all portions of the active 

 spark participated equally in the effect. A 

 change in the metal of which the electrodes 

 were made was also without noticeable in- 

 fluence. 



5. On the other hand, the sensitiveness of 

 the passive spark appeared to depend greatly 

 on its character. Long zigzag sparks be- 

 tween points were scarcely affected at all 

 by the presence of the active spark. The 

 influence of the latter was best shown in 

 the case of short sparks (1 mm. long) be- 

 tween brightly polished spheres of about 

 5 or 10 mm. diameter. Different parts of 

 the passive spark appeared to be sensitive 

 to the effect in different degrees. By screen- 

 ing various portions of the spark gap it was 

 found that the effect was much greater when 

 the negative pole was exposed. Hertz was 



unable to make sure, however, that the ac- 

 tion occurred exclusively at the negative 

 terminal. 



6. A noticeable gain in sensitiveness was 

 obtained by reducing the air pressure at the 

 passive spark, a maximum being reached 

 at about 100 mm. Only slight differences 

 were observed when other gases were sub- 

 stituted for air. 



7. Most substances, when used as screens, 

 were found to destroy the effect. Some, how- 

 ever, were in greater or less degree trans- 

 parent. The following is a partial list of 

 the materials tested by Hertz : 



Opaque. — Metals, even in extremely thin 

 sheets ; paraffin, sealing wax, rosin, rubber ; 

 glass, porcelain, wood, paper, ivory, leather, 

 mica, most crystals ; liquid paraffin, benzol, 

 petroleum, liquid COj, strongly colored so- 

 lutions, as fuchsin ; various salt solutions, 

 especially the copper and iron salts. 



Partially transparent. — Sugar crystals, 

 alum, calcite, rock salt. 



Transparent. — Quartz, even in thick pieces, 

 water, sulphuric acid, alcohol, ether. 



A number of gases were tested, and in 

 some cases (e. g., burning gas) were found 

 to be somewhat opaque. 



8. By changing the relative positions of 

 the two spark gaps it was shown that the 

 effect proceeded from the active spark in 

 all directions and in straight lines. The 

 shadow cast by a screen was sharply 

 defined ; on gradually sliding a screen 

 between the two sparks the effects ceased 

 at once when the passive spark passed 

 within the geometrical shadow. Reflec- 

 tion occurred at most surfaces in the 

 same manner as with light. The rays also 

 suffered refraction, being bent out of their 

 course more than light rays. By using 

 a prism of quartz it was found that the 

 active rays lie far beyond the extreme 

 violet of the visible spectrum. Attempts 

 to obtain phenomena analogous to double 

 refraction were unsuccessful. 



