258 report — 1879. 



tending to become parallel to the hypothetical Amperian currents, and to rotate in 

 an opposed sense around the pole. Further, a liquid vein carrying a current falling 

 upon the pointed pole of a vertical magnet is twisted, the sense of the torsion depend- 

 ing on the direction of the current and the polarity of the magnet. The author has 

 also essayed to extend his observations to the case of liquid jets which break in the 

 air, and which, therefore, cannot carry electric currents proper, but only electric 

 convection currents, and the results obtained, though not yet completed, dispose 

 him to include in this set of phenomena the so-called diamagnetism of flames and 

 of jets of smoke and steam. 



10. On a Hypothesis concerning the Ether in connection ivith Maxwell's 

 Theory of Electricity. By Dr. 0. J. Lodge. 



11. On a Neiv Electrometer Key. 1 Dr. 0. J. Lodge. 



12. On Improvements in Dynamo-Electric Machines. 

 By W. Ladd, F.R.A.S. 



My object in this communication is to describe in a few words the peculiarities 

 and improvements in the construction of Weston's dynamo-electric machine. 



The field magnets are composed of iron plates placed side by side in a mould, 

 but separated a uniform distance from each other. The iron magnets on which 

 the wire is to be wound are cast on to •' lugs' or projections on the ends of the 

 plates. The two cast-iron ends and uniting plates form one magnet. The upper 

 and lower magnets are alike, and when joined together by the perforated vertical 

 supports, the inner curved edges of the field plates embrace about two-thirds of 

 the circle in which the armature is made to revolve. The armature is built up 

 of plates which are somewhat like a cogged-wheel in shape. These are stamped 

 out of sheet iron, and when mounted on the shaft are separated from each other at a 

 uniform distance. The radial projections are then arranged in lines, so that the 

 whole forms a very broad cogged-wheel or cylindrical structure, having longitudinal 

 grooves with transverse spaces at regular distances. The longitudinal grooves are 

 for carrying the wire, and it will be observed from the nature of the structure that 

 the wire lies in channels three sides of which are iron, so that the mutual effect 

 upon each other is increased as much as possible. 



The ends of the wires are connected to the field magnets and commutator in 

 much the usual way, the currents travelling in one direction only. The commu- 

 tator is fitted on a portion of the shaft which projects beyond the bearings ; this 

 admits of its easy removal and a new one being replaced in three minutes. 



Another important feature in the construction is the arrangement for ventila- 

 tion. The separation between the pole plates of the field magnets, the perforations 

 in the vertical supports of the magnets, and the light framework of the armature, 

 are all for this purpose. The air enters the centre of the armature and is driven 

 out between the layers of wire through the spaces formed by the separated plates 

 of the armature and the field magnets, and thus prevents any part from becoming 

 unduly heated. 



Machines of this description are made of various sizes and strengths, and give 

 from one to sixteen lights in single circuit. 



1 The instrument was exhibited. 



