284 Mr. W. H. Preece on some Physical Points 



and at a given rate, the intensity of magnetism will increase 

 and decrease with the same ratio and at the same rate. 

 The disk d is elastic, but it is rigidly fixed at its axis ; 

 it being of iron, it is attracted at any moment with a force 

 dependent upon the intensity of the magnetism of the core 

 n s, and being elastic, it recovers, or tends to recover, 

 its normal position whenever this intensity of magnetism 

 ceases or diminishes. Thus, if the magnetic intensity varies, 

 the force of attraction varies, and the rate of motion of 

 the disk varies in the same way. Hence the disk will record 

 exactly the variations of the currents ; and as the currents 

 are the result of the variations of the vibrations of another 

 disk, the one disk c' simply repeats exactly the vibrations 

 of the other disk : thus sounds are reproduced. 



Though in the earlier instruments the coil surrounded a 

 pole-piece of soft iron, this pole-piece has since been discarded, 

 and the coil surrounds the pole of the magnet itself. The 

 efficacy of the instrument has been in no way impaired by this 

 change ; and it has the additional advantage of being perfectly 

 reversible, the same instrument being used for speaking and 

 for hearing. 



III. Working the Telephone* 



There is a remarkable difference in the power of different 

 voices to work the telephone. Shouting is of no use. The 

 intonation must be clear and the articulation distinct, and the 

 style of conversation approach more the sing-song. I have 

 heard Mr. Willmot, one of the electricians of the Post Office, 

 through resistances that have drowned all other voices. The 

 vowel sounds always come out the best ; the palatal sounds 

 c, #, j, k and q, the worst ; in fact, the latter sounds are fre- 

 quently lost. The ear also requires a certain education ; and 

 the power of hearing varies surprisingly with the different 

 ears and with different people. Singing always comes through 

 with remarkable distinctness ; and the sounds of a wind-instru- 

 ment — the cornet or the bugle — are reproduced with startling 

 force. A bugle sounded in London was heard distinctly over 

 the large Corn Exchange of Basingstoke by a thousand people. 

 This arises from the regularity as well as increased amplitude 

 of the sonorous vibrations, and consequently from the regu- 

 larity, uniformity, and increased strength of the currents of 

 electricity. 



IV. Improvements. 



Every one who has the means at his disposal has been en- 

 deavouring to increase the power of this instrument. I should 

 be sorry to enumerate the number of experiments I have 



