242 Mr. E. H. M. Bosanquet on Practical Electricity. 



The A Gramme machine has four electromagnets, two above 

 and two below, whose axes are in one plane. In the same 

 plane is the axis of the Gramme ring armature. The resis- 

 tance of the machine is about 1*2 ohm. 



The magnet-wires are directly connected with the armature- 

 brushes; and the terminals receive the wires after each has 

 passed through two magnets. Consequently all currents have 

 to pass through both magnets and armature, thus: — 



Magnet Armature Magnet 



Magnet Magnet 



Terminal Terminal 



For purposes which will be presently described, it was 

 found necessary to be able to separate the magnets from the 

 armature. The wires were therefore cut, by which means 

 the following combinations were obtained : — 



I — Magnet-terminals — i 



Magnets— r-Armature— Magnets 



Armature-terminals 

 and 



I — Magnet-terminals — i 



l Magnets 1 



1 — ■ A r ma tu re 1 



1 — Armature-terminals — ' 



in which last arrangement the magnets are separately excited. 

 There are other forms, which will be described presently. 



The resistance of the magnet circuit is about *75 ohm. 

 That of the double course through the armature is therefore 

 about "45 ohm, the total resistance being taken at 1*2. 



The terminals are marked + and — respectively. When 

 the machine is acting in correspondence with these indications, 

 I call it " straight," and the upper pole-piece attracts the un- 

 marked end of a compass-needle. The residual magnetism 

 is very strong. I think the whole of the solid part is probably 

 made of cast iron. 



