854 3fr. T. Thome Baker [April 22, 



the period taken to transmit a picture, one gaining on the other quite 

 an inappreciable amount, depending on the friction of the brush 

 against the pins. By this means the two cylinders are kept in very 

 fair synchronism independently of any wireless communication, and 

 the less the interval between the stopping and restarting of the cylin- 

 ders be made, the more accurate and satisfactory will be the effect. 



The other method of synchronising is controlled by electromagnetic 

 oscillations. Let us suppose that a coherer is being used as cymoscope, 

 the transmitting cylinder is kept running without any interruption, 

 but by means of a fleeting contact it sends out a wave at the conclu- 

 sion of its turn, a bare space in the picture being necessary about 

 half a second beforehand, so that no waves are sent out for the half- 

 second previously. The receiving cylinder is driven too quickly, 

 and checked at the end of the revolution. It then by means of a cam 

 pressiug down a spring lever throws out of circuit the marking 

 current and brings into circuit the relay which actuates the electro- 

 magnetic release. Consequently, when the synchronising wave is 

 received, the coherer causes the relay to work, the release is effected, 

 and the receiving cylinder starts a new revolution in unison with the 

 transmitter. 



This means of synchronising is only possible in cases where a 

 cymoscope is employed that is capa])le of actuating a relay, and you 

 will therefore see that it is out of the question except for short 

 distances. I am therefore using the chronometric system already 

 described in the apparatus, and it is being embodied in the quartz 

 fibre apparatus I am now about to describe. I must first remark 

 that the wireless work has been greatly facilitated by the courteous 

 assistance so readily given by the Marconi Company. 



The general form of the Einthoven galvanometer is well known, 

 and the modified type of it used by Professor Korn for photo- 

 telegraphic purposes has been already shown. If now we make the 

 magnetic field very much more intense by building the field magnets 

 heavier, and using a large number of ampere turns in the winding, 

 and also employ a " string," which is very much more elastic than 

 the silver ribbon, the displacement of the string will be correspond- 

 ingly greater. The silvered quartz fibre used by Duddell for this 

 purpose gives an extremely sensitive instrument, and very appreciable 

 displacement is obtained with the current from one dry cell passing 

 through 35 to 90 megohms resistance. 



It is not long since Professor Fleming explained at this Institu- 

 tion the valve receiver for detecting wireless oscillations ; in ordinary 

 wireless telegraphy the minute alternating currents are rectified, and 

 sounds are heard in the telephone in circuit owing to small uni- 

 directional currents. If these currents be passed through the silvered 

 quartz string of the galvanometer the string is shifted. If, therefore, 

 we cause a shadow of the string to lie over a fine slit any displace- 

 ment will cause the slit to be opened, as it were ; the shadow will be 



