4:4:8 APPENDIX. 



APPENDIX K. 



Electroscopes. (See 332.) For directions for making 

 simple and efficient electroscopes, see Tyndall's ''Lessons on Elec- 

 tricity," 7. For an electroscope for the electrophorus ( 343), pro- 

 vide a bit of wire about 8 em. long, and bend it at right angles about 

 1 cm. from each end. Solder one of the bent arms of the wire (see 

 Appendix B) to the upper side of the tinned plate, near its edge, in 

 such a way that the central part of the wire shall be vertical. Cut a 

 strip of gold-leaf (or Dutch metal) about 8cm. long and 8mm. wide. 

 Moisten the sides of the free horizontal wire arm with a little 

 mucilage, place the middle of the gold-leaf strip over the top of the 

 arm, and bring the ends of the leaf down to a vertical position, 

 touching each other. The mucilage will hold the leaf to the wire. 

 When the wire support and gold-leaves are electrified, the latter 

 will diverge. When the apparatus is not in use, this electroscope 

 may be protected by inverting a tumbler or beaker glass over it. 



APPENDIX L. 



Thermo-Electricity. (See 412.) The frame may be sim- 

 plified by bending a strip of copper twice at right angles to make 

 the top, bottom and one end of the frame, the other end being a 

 cylinder of bismuth. But the form shown in Fig. 207 is prefer- 

 able, as the same junction may be heated by the lamp below or 

 chilled by laying a piece of ice on the upper side. 



APPENDIX M. 



The Telephone. (See 446.) The theory that the diaphragm 

 of the receiving telephone is made to vibrate to and fro by the vary- 

 ing intensity of the magnetic attraction of the iron core has lately 

 been questioned. Many experiments go to show that the variations 

 in the magnetic intensity of the iron core are too feeble to produce 

 such mechanical effects. It also appears that paper and other sub- 

 stances may replace the iron of the diaphragm in the receiving tele- 

 phone, without destroying the sounds, and that the diaphragm may 

 even be removed and the sounds still produced and transmitted to 

 the ear. These facts are believed to show that the reproduced sound 

 is due to movements of the molecules of the iron core, such molecular 

 motions being due to the electric currents from the " transmitter " (or 



