In case the machine is out of order it should be removed from the outer case and the cause sought out and remedied. There are no delicate parts or mechanism and the machine may be examined without fear of injury. The only faults which have been observed are the collecting of dirt between the shells of the commutator and the commutator springs, want of contact between them and the collecting of metallic dust between the two shells of the commutator. Each of these faults may be remedied in a moment. It is proper to say that these faults have never occurred when the machines were turned by hand and seldom when turned by power at a high rate of speed. Some of the wire connections inside the machine might be severed by the breaking of a soldered joint, of which there are five. A fault of this kind would be readily found and easily remedied. In soldering electrical connections, resin, and not acid, should be used. The effect of any of these faults is to cause a break in the continuity of the electrical circuit of the machine. This circuit is as follows: starting from one binding-screw, a wire leads to the field-of-force coils, or electro-magnet coils, traverses them and passes to one of the commutator springs; thence to one shell of the commutator; thence to the coil around the armature, through this coil to the other shell of the commutator; thence to the other commutator spring and, by a wire, to the second binding-screw, thus forming a complete circuit, when the binding-screws are joined together. If they are left unconnected, there is no closed circuit, no current is generated and the armature, therefore, turns easily. When the circuit is closed by connecting the terminals by a conductor of not too great resistance, the current generated excites the electro-magnets and this leads, in turn, to the generation of a stronger current until a maximum is reached depending on the resistance of the circuit and the speed with which the crank is turned. The electrical energy thus developed when the circuit is closed requires, of course, that extra work should be done to turn the crank. When the circuit is broken, inside or outside of the machine, it is necessary to overcome only the friction of the machine and the armature, therefore, turns easily.