62 2 THE POPULAR SCIENCE MONTHLY. 



only one four-liundredth as much over a given wire as it would 

 be if transmitted at fifty volts. 



The advantage that alternating currents have over direct for 

 long-distance transmission is that they may easily be transformed 

 up or down that is, their voltage at the generating end may be 

 increased (at the expense, of course, of their amperage) and re- 

 duced at the consuming end. In point of fact, it is frequently 

 and usually unnecessary to employ such devices at the generat- 

 ing end, for the reason that the generators themselves can work 

 perfectly well at the high voltage requisite to transmit. The ob- 

 jection to using the same high voltage on the consuming machin- 

 ery is simply that there is more danger of accident with numer- 

 ous small motors scattered in various places and in the hands of 

 unskilled persons than in a power station containing only two or 

 three highly guarded machines attended by trained operatives. 



With this fact of the possibility of generating currents of a 

 voltage suitable for immediate transmission, it at first sight 

 appears strange that direct-current transmission is not a more 

 common thing than it is. The method of the so-called "motor 

 transformer," " rotary transformer," or " dynamotor," might be 

 adopted. A transmission plant working on this method would 

 operate as follows : The power station would contain preferably 

 several highly insulated direct-current generators, all of similar 

 construction, for very high potential (four thousand volts would 

 be easily obtained) ; these would run in series that is, each would 

 add its voltage to that of the others, and there would preferably 

 be a spare machine to substitute for any one of the others which 

 might become injured. If four machines were in series, the re- 

 sultant current would be put to line at, say, sixteen thousand 

 volts, would be received at the other end by a number of motors, 

 also in series, which in their turn would drive low potential dyna- 

 mos supplying current for local use. 



There are two objections to this as compared with alternating- 

 current transmission : One is the fact that there has grown up a 

 very tangible, we may almost call it, superstition against the use 

 of high-voltage direct-current machines of large size among very 

 many electricians. The reasons for this are not difficult to trace ; 

 prominent among them being the simple fact that no commercial 

 application has ever yet required such machines. The only high- 

 potential direct-current dynamos are those used for arc lighting, 

 and on account of the great subdivision of arc-lighting circuits 

 the units of generation are invariably small, at least by com- 

 parison with the ponderous machinery used in the Niagara 

 Falls power plant. 



There is no reason why they could not be made large (in point 

 of fact, arc-lighting requirements are continually making demands 



