S7A WILLIAM SIEMENS, F.R.S. 397 



the amount of effect either in quantity or in potential which I can 

 command. I will now ask Mr. Nebel to connect this wire, and you 

 will see that we have here between these points such a potential 

 thai a spark similar to a lightning discharge takes place across 

 ip, about an inch long, between them. This represents, 

 electrically speaking, a very high potential probably 80,000 

 volts. 



The machines which we have so far considered depend for their 

 action upon the severance of an armature from a permanent 

 magnet. In the year 1865 another principle of action saw the 

 light of day. It was first communicated by my brother, Werner 

 Siemens, to the Berlin Academy; it was also communicated by 

 myself to the Royal Society three weeks later, and when my Paper 

 was read Professor Whcatstone brought the same idea forward. 

 The principle consists in this, that when the current produced by 

 the severance of an armature surrounded by conducting wire from 

 the poles of an electro-magnet, is sent through the coils of the 

 very magnet that produces the magnetism, a kind of regenerator 

 action is set up. There must be a magnetic field to commence 

 the action, and in our first experiments, this initial amount of 

 magnetism was produced by means of a small battery connected 

 with a separate coil on the electro-magnets ; we; soon found, 

 however, that no such initial excitement was necessary, but that 

 terrestrial magnetism sufficed to induce in the bars of the electro- 

 magnets a magnetic action sufficient to cause a slight current in 

 the coils of the rotary armature, which, in passing through the 

 coils of the field magnets, increased their magnetic tendency ; the 

 result was an increased inductive action, and an increased induced 

 current ; this again, in passing through the coils of the field 

 magnets, further increased the magnetic intensity, giving rise to 

 increased inductive action, and to a current of increased intensity. 

 The accumulative action thus set up is limited, however, by the 

 point of magnetic saturation of which a bar of iron is capable. 

 Up to that point the resistance of the rotary armature rapidly 

 increases, thus causing a direct conversion of mechanical into 

 electrical energy. This is the principle upon which dynamo- 

 machines are now generally conceived, and it gives us a power 

 of increase which Faraday foresaw in his original experiment, 

 when he said that the time would come when the primary eflect 



