HERTZIAN ^VAYE WIRELESS TELEGRAPHY. 443 



Tcumatology , and in view of our familiarity with such terms as micro- 

 scope, electroscope and liygroscope, tliere does not seem to be any objec- 

 tion to enlarging our vocabulary by calling a wave-detecting appliance 

 a Jcumascope. We are then able to look at the subject broadly and to 

 classify kumascopes of different kinds. 



We may, in the first place, arrange them according to the principle 

 on which they act. Thus, we may have electric, magnetic, thermal, 

 chemical and physiological operations involved; and finally, we may 

 divide them into those which are self-restoring, in the sense that after 

 the passage or action of a wave upon them they return to their original 

 sensitive condition; and those which are non-restoring, in that they 

 must be subjected to some treatment to bring them back again to a 

 condition in which they are fit to respond again to the action of a 

 wave. 



We have no space to refer to the whole of the steps of discovery 

 which led up to the invention of all the various forms of the modern 

 electric kumascope or wave detector. Suffice it to say that the re- 

 searches of Hertz in 1887 threw a flood of light upon many previously 

 obscure phenomena, and enabled us to see that an electric spark, and 

 especially an oscillatory spark, creates a disturbance in the ether, 

 which has a resemblance in nature to the expanding ripples produced 

 by a stone hurled into water. Scientific investigation then returned 

 with fresh interest to previously incomprehensible effects, and a new 

 meaning was read into many old observations. Again and again it had 

 been noticed that loose metallic contacts, loose aggregations of metallic 

 filings or fragments, had a mysterious way of altering their con- 

 ductivity under the action of electric sparks, lightning discharges and 

 high electromotive forces. 



As far back as 1852, Mr. Varley had noticed that masses of 

 powdered metals had a very small conductivity, which increased in a 

 remarkable way during thunderstorms;* and in 1866, C. and S. A. 

 Varley patented a device for protecting telegraphic instruments from 

 lightning, which consisted of a small box of powdered carbon in which 

 were buried two nearly touching metal points, and they stated that 

 'powdered conducting matter offers a great resistance to a current of 

 moderate tension, but offers but little resistance to currents of high 

 tension.'! 



We then pass over a long interval and find that the next published 

 account of similar observations was due to Professor T. Calzecchi- 

 Onesti, who described in an Italian journal, II Nuovo Cimento (see 

 Vol. 16, p. 58, and Vol. 17, p. 38), in 1884 and 1885 his observations 

 on the decrease in resistance of metal powders when the spark from an 



* The Electrician, Vol. XL., p. 86 (Leader). 



f British Pateyit Specification, C. and S. A. Varley, No. 165, 1866. 



