Dec. 28, 1883.] 



♦ KNOWLEDGE . 



391 



of a coil or ring of iron wire over which a series of coils 

 of copper wire are wound. These coils are continuous, that 

 is to say they are side \<j side, and so form a compact ring 

 in which the iron core is entirely covered. This ring in 



Fig. 3. 



being fixed has to be forced on to a wooden spindle, so 

 that in revolving the rotation of the ring is dependent 

 upon the friation between the cotton-covered wire and the 

 ■wood. As the tendency of the current in the inducing or 



ingly good and almost perfect. Six, eight, or more such 

 rings are placed on the spindle, and constitute the arma- 

 ture. In the Gramme machine contiguous coils are con- 

 nected together, and in the Brush machine, it may be 

 remembered, the opposite coils are connected ; but in the 

 Biirgin machine the connection is materially different, very 

 novel, but also very ingenious. The arrangement is to 

 connect, say, the first coil of the first ring to the coil of the 

 second ring which is next behind it, and thence to the next 

 succeeding coil of the third ring, and so on, each ring being 

 one forty-eighth of a revolution behind the one electrically 

 in front of it. (See Fig. 3 ) Supposing the armature to 

 have six rings, the sixth coil of the sixth ring is connected 

 to the second coil of the first ring, which is again connected 

 to the third coil of the second ring, and so on till the series 

 is completed. This gives to the armature all the advantage 

 of the Gramme ring, besides which it is worth noting the 

 open nature of the structure, and the absence of non-con- 

 ducting materials helps very materially to keep the machine 

 cool, a highly-desirable result, which is further assisted by 

 the comparatively very small quantity of copper wire 



field magnets is to arrest rotation (otherwise no current 

 could be generated in the ring), it is manifest that to 

 attain high velocities with safety, some device of a higher 

 mechanical order is desirable. This is one of the many 

 advantages pertaining to the Biirgin dynamo. The arma- 

 ture (Fig. 3) consists, not of one but if a number of 

 rings, each ring being composed of a coil of soft iron wire 

 pressed out into a hexagonal shape, so that there are six 

 corners, all of which would be touched by a circumscribing 

 circle. On each straight section of the iron core — or, 

 in other words, on each side of the hexagon — are 

 wound five layers of cotton-covered wire (W, Fig. 4), 

 each layer being shorter than the subjacent one, so as 

 to give, when the six coils arc finished, an approxi- 

 mately complete circle externally. A piece of gun-metal 

 (J), star like in shape, with six spokes or radiations, 

 is then forced very firmly into the ring, each spoke 

 finding its position in one or other of the corners of the 

 hexagon. The gun-metal star has a hole in the centre 

 through which an iron spindle (S) is passed and made rigid. 

 It will thus be seen that the mechanical virtue is exceed- 



employed. It must not be forgotten that apart from the 

 mechanical objection to heating, an increase of tempera- 

 ture affects adversely the resistance of the wire. The com- 

 mutator, or that part of the machine where the current is 

 made to pass out of the armature into the field-magnets 

 and tlie external surface, is similar to the Gramme, the 

 junction of each pair of coils being connected to the same 

 sectional strip of pliosphor bronze (a very durable metal 

 ■which is used for the purpose). >'ot the least of the ad- 

 vantages emliraced in JI. Biirgin's invention is the great 

 facility with which the armature may be taken to pieces 

 for examination or repairs. 



The generating or field magnets (M, M) are well depicted 

 in Figs. 1, 2, and i. The whole of the iron framework and 

 the cores of the magnets are cast in t-n-o pieces, one of 

 which is placed above and the other beneath the armature. 

 The cores are of oval section, and the wire is so wound as 

 to make the two crescent-shaped pole-pieces, which almost 

 envelope the armature, of opposite polarity. 



Want of space compels us to defer for a fortnight the 

 completion of our remarks on this dynamo. 



