1889.] Address. 103 



order to protect the signallers from the destructive effects of lightning. 

 Hitherto the so-called " plate-lightning-discharger " has been in general 

 use in India. The upper plate has two screws, to one of which is connected 

 the line wire entering the office, and to the other the telegraph apparatus. 

 The lower plate is connected direct to the earth. The two plates on 

 the sides facing each other are finely grooved in parallel lines, the 

 grooves in the line-plate crossing those in the earth-plate at right 

 angles, so that each crossing approximately represents two cones with 

 their points facing each other, with a small space of air between 

 them ; and the more numerous such crossings, and the smaller the air- 

 space, the more efficient the discharger. 



However, actual experience in India and, very recently, a long series of 

 laboratory experiments, certainly seem to show that a greater amount of 

 protection can be obtained by employing two perfectly smooth metal 

 surfaces separated only by a thin sheet of mica, two or three circular 

 holes being cut in the mica to admit of the discharge passing between 

 the plates and so to earth. The reason of this greater protection lies in 

 the fact that mica possesses at least five times greater capacity or power 

 of drawing in charges of electricity than air has. For example, if 

 two comparatively small plates separated by mica, and two much larger 

 plates separated by air are connected up ' parallel ' or ' in series,' in a 

 circuit in which currents of high potential are generated, it will be ob- 

 served that the sparks all pass between the mica-separated plates and 

 none at all between the air-separated ones. 



It may be noted that in 1846 Steinheil used a plate-discharger with 

 a sheet of silk as the insulating medium, the principle of action involved 

 being in a lesser degree exactly that of the new mica discharger. 



The use of telephones is extending, and during the year they have 

 been adopted in the Harbour Defence Works, Bombay and Karachi, for 

 giving orders and information. They have been found useful in the con- 

 struction of railways and, especially, in difficult tunnelling works. Also iu 

 station-yards, where it is necessary for a Station-master to convey simul- 

 taneous orders to three or more signal-boxes regarding the shunting of 

 trains &c. They have been used at rifle ranges instead of the old 

 system of flags, or in addition to it. 



A system for recoi'ding the hearing powers of persons, especially 

 those under treatment for deafness, by means of an arrangement of 

 telephone and electrical resistance has been devised aud will no doubt 

 be tried in our hospitals. A record of hearing can be kept as accurately 

 as a record of weight is now kept. 



Electric lighting is slowly making its way in India, but the almost 

 prohibitive cost of installation prevents its extended adoption in place 

 of gas. 



