Dynamo- Electric Machinery. 



49 



March 17, 1892. 



Sir GABRIEL STOKES, Bart., LL.D., Vice-President, in the Chair. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



The following Papers were read : — 



I. " Dynamo-Electric Machinery." By J. HOPKINSON, F.R.S., 

 and E. Wilson. Received February 15, 1892. 



The following is intended as completion of a paper by Drs. J. and 

 E. Hopkinson (' Phil. Trans.,' 1886, p. 331) * The motive is to verify 

 by experiment theoretical results concerning the effect of the currents 

 in the armature of dynamo machines on the amount and distribution 

 of the magnetic field which were given in that paper, but which were 

 left without verification. For the sake of completeness, part of the 

 work is given over again. 



The two dynamos experimented upon were constructed by Messrs. 

 Siemens Brothers and Co., and are identical, as far as it is possible to 

 make them. They are mounted upon a common base plate, their 

 axles being coupled together, and are referred to in this paper 

 respectively as No. 1 and No. 2. 



Each dynamo has a single magnetic circuit consisting of two 

 vertical limbs extended at their lower extremities to form the pole- 

 pieces, and having their upper extremities connected by a yoke of 

 rectangular section. Each limb, together with its pole-piece, is 

 formed of a single forging of wrought iron. These forgings, as 

 also that of the yoke, are built up of hammered scrap iron, and after- 

 wards carefully annealed. Gun-metal castings bolted to the base- 

 plate of the machine support the magnets. 



The magnetising coils on each limb consist of sixteen layers of 

 copper wire 2 mm. diameter, making a total of 3968 convolutions for 

 each machine. The pole-pieces are bored out to receive the armature, 

 leaving a gap above and below subtending an angle of 68° at the 

 centre of the shaft. The opposing surfaces of the gap are 1*4 cm. 

 deep. 



* It must not be supposed from his name not appearing in this short paper that 

 my brother, Dr. E. Hopkinson, had a minor part in the earlier paper. He not only 

 did the most laborious part of the experimental work, but contributed his proper 

 share to whatever there may be of merit in the theoretical part of the paper.-— J. H. 



VOL. LI. E 



