UEirrZIAN WAVE WIEELESS TELEGRAPHY. 551 



HERTZIAN WAVE WIRELESS TELEGRAPHY. V. 



By Dr. J. A. FLEMING, F.R.S., 

 PROFESSOR OF ELECTRICAL ENGINEERING, UNIVERSITY COLLEGE, LONDON. 



QUITE recently, Sir Oliver Lodge and Dr. Miiirhead have era- 

 ployed as a self-restoring coherer or kiimascope a steel disc 

 revolved by clockwork, the edge of which just touches a globule of mer- 

 cury covered with a thin film of paraffin oil. The contact is made 

 between the mercury and the steel by the electric wave generating an 

 electromotive force in the aerial, sufficient to break through the thin 

 film of oil. When the wave stops, the circuit is again interrupted 

 automatically. 



This device is used without a relay to actuate directly a syphon 

 recorder as used in submarine telegraphy. The working battery em- 

 ployed with it must only have an electromotive force of about a tenth 

 of a volt. It may be used also with a telephone in circuit and can 

 therefore be employed either for telegraphic or telephonic reception.* 



One of the most sensitive of these self-restoring kumascopes is the 

 carbon-steel-mercury coherer, the invention of which has been attrib- 

 uted to Castelli, a signalman in the Italian Navy,! but also stated on 

 good authority to have been the invention of offi- 

 cers in the Royal Italian Xavy, and has there- 

 fore been called the Italian Navy Coherer.;}; 

 This instrument has been arranged in several 

 forms, but in the simplest of these it consists of 

 a glass tube, having in it a plug of iron and a 

 plug of arc-lamp carbon, or two plugs of iron 

 with a plug of carbon between them. The 

 plugs of iron, or of iron and carbon, are sepa- 

 rated by an exceedingly small globule of mer- 

 cury, the size of which should be between one 

 and a half and three millimeters. The plugs 

 closing the tube must be capable of movement, 

 one of them by means of a screw, as shown in the diagram (Fig. 17), 

 taken from a patent specification communicated to Mr. Marconi by the 



* See Proc. Roy. Soc. London, Vol. LXXI., p. 402. 



t See Report by Captain Quintino Bonomo, ' Telegrafia senza fili,' Rome, 

 1902; L'Elettricista, Ser. II., Vol. I., pp. 118, 173. 



t See Royal Institution, Friday evening discourse, by Mr. Marconi, June 

 13, 1902. Also The Electrician, Vol. XLIX., p. 490. Also a letter to the 

 Times of July 3, 1902, by the Marchese Luigi Solari. 



B 







7 



^ 



W 



__P^ 



C M I 



IK ■ 



^V ^. ' ^iL/J ' ^^ * 



Fig. 17. Italian Navy 

 Self-Restoring Kuma- 

 scoPE. C, carbon plug; 

 /, iron plug ; M, mercury 

 globule; A, aerial ; B, bat- 

 tery ; T, telephone ; 8, ad- 

 justing screw. 



