ALT~nATI~G-CURR~nT OEN~.~ATORS. We have already seen that direct-current machinery had become somewhat standardized by I89o, and that the Hobart machine, described on page 22, has design constants and a type of mechanical construction which do not differ much from those of Fro. 32. Belt-driven single-phase alternator, 90 k.w., I6,OOO alternations. similar machines of recent date, but at that time, 27 years ago, there was no one type of alternator that was considered superior to all others. The first Niagara machines, shown in Fig. 3, had an external rotating field system, this type of construction being considered necessary to give the large flywheel effect required to maintain * Continued from page 48, July issue. 205