so far as to throw doubt upon it; for in his first publication he said that his discovery might possibly have some use in the construction of electricity meters, but that it would probably be useless for electric motors. Yet more than half the motive power produced electrically nowadays is produced in machines in which the discovery made by Ferraris is utilised. Pacinotti was content to utilise his invention for his own scientific experiments, but he did not apply it for industrial purposes. This was done by Zenobe Theophil Gramme in 1869. It is very probable that Gramme, who at the time was employed as pattern-maker in an electrical manufacturing firm, had never heard of Pacinotti’s invention. He re-invented the spiral winding and the many-part commutator; and recognising the practical importance of this invention he patented it in 1869. Hence this type of armature winding is called a "Gramme winding," or also a "Gramme Ring" or a "Ring Winding." It is diagrammatically represented in Fig. 17. S N are the poles of the field-magnet system so shaped as to produce a polar cavity in which the armature revolves. This consists of an iron ring R wound with insulated copper wire, the winding
