in Magnetism and Electricity. 101 



" quantity w effects. These armatures are made of cast iron, and 

 are precisely alike in dimensions, as they were cast from the 

 same pattern. The thickness of the rib G, fig. 5, uniting the 

 segmental sides of the armatures, is 1*75 inch, and the latter are 

 turned one-eighth of an inch less in diameter than the bore of 

 the magnet-cylinder. A pulley, 10 inches in diameter, is keyed 

 upon one end of each armature, and upon the other end is fixed 

 a commutator, by means of which the waves of electricity from 

 the armature can be taken, either in the same or in alternate di- 

 rections as required (15, 16). 



71. The intensity armature is coiled with an insulated con- 

 ductor consisting of a bundle of thirteen No. 11 copper wires, 

 each 0*125 of an inch in diameter, the same as that coiled round 

 the sides of the electromagnet (68). The conductor is 376 feet 

 in length and weighs 232 lbs., and is covered with a casing of 

 wood extending the entire length of the armature, for the pur- 

 pose of protecting it from external injury. Strong bands of 

 sheet brass 1 inch in width encircle the armature at intervals of 

 6 inches, for the purpose of keeping the casing and the convo- 

 lutions of the conductor in position during their rapid revolution 

 (11). The total weight of this armature with all its fittings is 

 0'3 of a ton. 



72. The quantity armature is enveloped with the folds of an 

 insulated conductor consisting of four plates of copper, each 67 

 feet in length, 6 inches in width, and one-sixteenth of an inch 

 in thickness. These plates are superposed in metallic contact 

 with each other so as to form a single copper plate one-quarter 

 of an inch in thickness, 67 feet in length, and nearly wide enough 

 to occupy the entire width between the segmental sides of the 

 armature. This division of the conductor into four plates was 

 made for the greater convenience of bending it round the arma- 

 ture. The inner extremity of the conductor is held in intimate 

 contact with the body of the armature by means of flat-headed 

 screws ; and the convolutions are insulated from one another by 

 placing between them a band of thick cotton and india-rubber 

 fabric, of the same length and width as the laminated conductor ; 

 and the edges of the latter are insulated from the sides of the 

 armature by means of thin pieces of wood. The outer extre- 

 mity of the conductor is terminated by a thick copper stud which 

 connects it with the insulated half of the commutator fixed on 

 the armature axis ; and the convolutions are retained in position, 

 by means of bands, in the same manner as those of the intensity 

 armature (11, 71). The weight of the laminated copper con- 

 ductor is 344 lbs., and the total weight of the armature is 0*35 

 of a ton. 



73. The armatures were accurately balanced before being 



