CONTENTS. Xlll 



Page 



9. Sand Batteries 228 



10. Alum Batteries 228 



11. Marie Davy's Proto- sulphate of Mercury Battery . . . 229 



12. Terra- Voltaism - . ; 230 



13. Amalgamated Zinc 231 



II. MEASUREMENT OF THE GALVANIC CURRENT. 



14. Voltameter 232 



15. Galvanometers 235 



16. Tangent Galvanometer . .'.'... '. . ... . . . 237 



17. Sine ,, 241 



18. Astatic Conditions of a Needle Pair 243 



19. Magnetism of the Coils .' : .' .' . . ... . . . 245 



20. Sine and Tangent Galvanometer 246 



21. Weber's Reflecting Galvanometer 247 



22. Thomson's ,, 249 



23. Eheostats Wheatstone's . ;..'.. -._" . . . . . 251 



24. ,, Jacobi's . .' : : ; . . . . . . . . 252 



25. ,, Poggendorff's . . .'. . .' -;" . . . . 253 



26. Siemens' Resistance Boxes : . . . . 253 



27. Eisenlohr's Resistance Column 255 



28. Ohm's Law , 256 



III. CONDUCTING POWERS or MATERIALS. 



29. Specific Conducting Powers . ..;.;...". . . . 264 



30. Pure metals - *- 266 



31. Influence of Temperature 266 



32. Alloys ^ 268 



33. .Effects of Annealing ' 269 



34. Fused Metals . ^ . ..... . . . 270 



35. Electric Permanency of Metals and Alloys . . . . . 273 



36. Fluids . ... . . . . ... 276 



37. Determination of Galvanic Polarisation 278 



38. Insulating Substances 280 



39. Influence of Temperature 282 



IV. METHODS OF CABLE-MEASUREMENT. 



40. Kirchhoff's Laws of Branch Circuits ...*'. ... 285 



41. Wheatstone's Balance 290 



42. Siemens' Apparatus for Testing Cables 294 



