SCIENCE. 



313 



tion. The sounds will be heard much louder, and 

 any other source ot eleciricily with high potential 

 will answer the same purpose. Hence a battery of a 

 large number of cells may be substituted for the Holtz 

 machine, and one of the terminals of the battery may go 

 to the ground, though this is net essential. This arrange- 

 ment will keep the teiminal plate charged to the poten- 

 tial due to the chemical relations and number of cells in 

 the battery. If the batteiy be placed in the line wire it 

 will keep both ends of the line charged. A Volta's pile 

 may be substituted for the battery in either place, and so 

 may a charged condenser of any capacity, the electrically 



Figure 8. 



charged terminals in this system acting in a way analo- 

 gous to the permanent magnets in the magnetic system. 



There are various other ways of employing condensers, 

 and as one would infer from the preceding descriptions 

 of the phenomena, these condensers will talk, that is, 

 they will reproduce in sound the varying electrical con- 

 ditions to which that may be subjected, as will also either 

 a battery or a Volta's pile. 



I have often heard them talk, and have made many 

 experiments with such receivers. 



By this system telephonic communication can be se- 

 cured through ordinary medical electrodes. 



In perfecting this new telephone Professor Dolbear 

 has given long and constant study to the scientific prob- 

 lems involved, while the mechanical construction has 

 been prosecuted by Mr. H. C. Buck, aided by skilled 

 machinists and competent assistants. The above con- 

 cise description in the inventor's own words will give our 

 readers a clear understanding of the principles that 

 underlie his interesting invention, and it only remains for 

 us to describe in brief the several figures in our front 

 page engraving. 



Fig. 7 shows the telephone in actual use, the transmit- 

 ter being secured to the wall, the battery and induction 

 coil being placed in a box on the floor, or in a convenient 

 closet. Fig. 4 is a perspective view of the new receiver ; 

 Fig. 2 a face view of the same, with a portion of the cas- 

 ing broken away to show the connection of the two bind- 

 ing posts, A B, with the diaphragms, C D, and the 

 adjusting screws by which the distance between the 



diaphragms is regulated are shown in the sectional view 

 Fig. 1. 



Fig. 8 illustrates the principle of electrical attraction 

 upon which the action of the new receiver is based ; the 

 electrostatic charge received by the plate, E, from the 

 induction coil attracts the pith ball suspended in front of 

 the plate. 



Fig. 6 shows the two plates, E, of an Epinus conden- 

 ser, placed near together and connected with the termi- 

 nals of the secondary wire of the induction coil, I, and 

 used as a telephone receiver. 



Figure 9. 



Fig. 5 illustrates the essential features of the new tel- 

 ephonic system. I being the induction coil whose pri- 

 mary is in circuit with the battery, B, and transmitter, T, 

 the receivers, R, are each connected with a single ter- 

 minal of the secondary wire of the coil, I. 



Fig. 9 shows Professor Dolbear's experimental tele- 

 phone transmitter. In this instrument the diaphragm, A, 

 is horizontal, and carries a carbon electrode, upon which 

 rests a moveable carbon electrode connected by an arm 

 with a delicately pivoted bar supported by the diaphragm 

 cell. The local circuit is from the battery, B, through 

 the carbon electrodes, and through the primary of the in- 

 duction coil, I. 



Extraction of Silver. — To extract the silver from silver- 

 ed objects, these should be plunged into a bath composed 

 of a mixture of 100 grammes of finely pulverised saltpetre 

 and 1000 grammes of sulphuric acid. Tf the acid is weak, 

 the copper and the other metals except the silver will be 

 attacked ; if the acid is concentrated the silver alone will 

 be dissolved. 



