In using the ordinary Bell telephone, it is necessary to speak distinctly before the mouthpiece of the telephone which is handled, while the listener placed at the corresponding station keeps the mouthpiece of the receiver to his ear. These two instruments form a closed circuit with the two wires which connect them, but one is enough to make the transmission perfect, if care is taken to place both instruments in connection with the earth, which thus takes the place of the second wire. M. Bourbouze asserts that the intensity of sound in the telephone is much increased by employing this expedient, but we believe that this increase depends upon the conditions of the circuit, although he asserts that the fact can be proved in a circuit not exceeding eighty yards. For practical purposes it is necessary to have two telephones at each station, so as to hold one to the ear while speaking through the other, as in fig. 23. It is also much more easy to hear with a telephone applied to each ear, in which case they are held as in fig. 24. In order not to fatigue the arms, an arrangement has been made by which they are held before the ears by a strap and spring which goes round the head. [Illustration: FIG. 23.] The sending power of the telephone varies with different voices. Mr. Preece asserts that shouting has no effect, and that, in order to obtain a favourable result, the intonation must be clear, the articulation distinct, and the sounds emitted must resemble musical sounds as much as possible. Mr. Wilmot, one of the electricians employed by the Post Office, says that he has been able to make himself heard on circuits through which no other voices were audible. The vowel sounds are most readily transmitted, and among other letters _e_, _g_, _j_, _k_, and _q_ are always repeated more imperfectly. The ear requires practice, and the faculty of hearing varies in a surprising degree in different people. Singing is very distinctly heard, as well as wind instruments, especially the cornet-à-piston, which, when played in London, was heard by thousands of people in the Corn Exchange at Basingstoke. [Illustration: FIG. 24.] According to Mr. Rollo Russell, it is not necessary to isolate the circuit of a telephone when the distance is relatively slight; thus, with a circuit of about 430 yards, it is possible to use a simple copper wire, laid on the grass, without destroying the telephonic transmission from a small musical box, as long as the two wires do not touch each other. Transmission took place, even when the circuit was buried in moist earth for a length of thirty-five yards, or immersed in a well for a length of forty-eight yards. The words transmitted under such conditions did not differ from those transmitted by an isolated circuit.