4 H ALDAN E Gee— //<';/ rr IVt'/de 



much as a piece of the same kind of paper when exposed for 

 one minute to the direct rays of the sun at noon on a very clear 

 day in March. 



These electro-magnetic generators had a very serious defect. 

 The eddy and other currents in the armature, being converted into 

 heat, produced a rise of temperature of 30o°F. and upwards. 

 Wilde found that the smaller generators ran cooler than those 

 of larger size ; but even the former, during long runs, got so hot 

 as to endanger the insulation. At a works where it was desir- 

 able to run the machines for days and nights without a stop, 

 water was passed round hollow brass segments forming part of 

 the armature cylinder, and the hot water produced was used to 

 feed the steam boilers. In order to obtain sufficiently large 

 currents it was necessary to run a number of the small genera- 

 tors in parallel. This led to a number of difficulties. Although 

 the armatures of the machines were driven with equal-sized, 

 pulleys from the same countershaft by belts, the want of perfect 

 synchronism prevented efficient parallel running. Wilde tried 

 gearing a pair of machines together, and he then made his most 

 important discovery. He ran the machines as alternators. When 

 the armatures were so clutched that the currents were in the 

 same phase, the sum of the currents was obtained in the main 

 circuit; but when they were clutched together so that the currents 

 were in opposite phase, no current resulted. He found now that 

 when the clutch was unfastened and the machines were run dis- 

 connected from one another, the armatures were pulled into phase 

 and they ran perfectly in parallel, so that no mechanical gearing 

 was necessary. Wilde had thus discovered that alternators can 

 run in parallel when synchronous. The full importance of this 

 was not realised until electrical engineering was more developed. 

 Subsequently, John Hopkinson showed that it was mathematically 

 possible; and now the parallel running of alternators is in every- 

 day use at supply stations. 



With the threefold object of obtaining a generator that would 

 heat less, that could be driven at a lower speed, and in which the 

 pulsations of the rectified current would not be so marked, 

 Wilde designed and constructed electro-magnetic machines of 

 a type entirely different from those previously described. The 

 details are given in a paper read before this Society in 1873. The 

 shuttle-wound type of armature was abandoned, and he used one 

 with 16 cylindrical bar magnets. The originator of this type of 

 armature is claimed for King in 1846. //',?■. 3 shows the details 

 of the machine. To each of the circular frames of cast iron 

 are fixed 16 electro-magnets. They are wound with insulated 

 copper wire and are joined up so that in the two circles the 

 adjacent poles and those opposite are of different polarity. The 

 armature bobbins are fixed on a heavy disc of cast iron. Four 

 of the bobbins are connected to a comnuitator; the alternating 



