December 12, 1884.] 



SCIENCE. 



525 



its first cost." The correctness of the principle has 

 been established by Sir William Thomson and oth- 

 ers. 1 



In the three-wire system, Edison reduces the cur- 

 rent to one-half its value in the two-wire system, 

 and increases the total resistance of the same number 

 of lamps to four times the former value, by the ar- 

 rangement shown in the second diagram of the arti- 

 cle referred to. The total heat-energy developed in 

 the lamps, then, remains the same, since it is rep- 

 resented by C' 2 r, where r is the combined resistance 

 of the lamps in multiple arc. The inference is, that 

 the resistance of the leading wires should also be 

 increased fourfold. In the articles referred to at the 

 bottom of the page ; it is shown that the cross-section 

 of the conductor should vary simply as the current 

 strength. Hence the conductors in Edison's three- 

 wire system should be diminished only one-half in 

 size for greatest economy of working. That this is 

 entirely correct will appear from an examination of 

 the energy expended in heating the leading wires in 

 the several cases. In the two-wire system 



E 



C = 



B + r 



(1) 



in which B and r are the resistance of conductors 

 and lamps respectively. In the three-wire system as 

 arranged by Edison 



In the three-wire system, with conductors half size, 

 2E' 



iC 



2R + 4r 



(3) 



in which E' equals the electromotive force of each of 

 the two dynamos in series. This electromotive force 

 can be lower than in cases one and two. From (1), 

 E=CB + Or, and EC= C 2 B + C 2 r, for total elec- 

 trical energy expended; the first term being the heat- 

 waste in the conductors, and the second the energy 

 expended in the lamps. 



From (2), E=CR + Cr, as before. The total en- 

 ergy is iC.2E= CE, the same as before. From (3), 

 E' — $CR + Cr, and the total electrical energy is 

 ±C . 2E = CE' = $C 2 B + C 2 r. The energy expend- 

 ed upon the lamps is the same in the three cases, 

 being represented by C 2 r ; but in the third case the 

 heat-waste is iC 2 B, or only one-half as much as in 

 the other cases. In Edison's arrangement the ratio 

 between energy expended in the lamps, and heat- 

 waste in the mains, is the same in his three-wire 

 system as in the two-wire system. If the conductors 

 be reduced to only half their former cross-section, 

 the ratio of heat expended in conductors to heat 

 developed in lamps is only half as great as before. 

 Edison saves 62.5 % of the cost of conductors, or 62.5 % 

 of the interest on their cost, the running-expenses 

 remaining the same. With half-size conductors, the 

 saving would be 25% in interest on cost of conductors, 

 and 5l> % in heat- waste on conductors, or a total of 75 %, 

 — a gain of 12.5% over the plan adopted by Edison. 

 Moreover, the electromotive force of each machine 

 being lower, the dynamos could be reduced in size, 

 and their cost would be less. In reducing the con- 

 ductors three-fourths in cross-section, the rise of 

 temperature for the same quantity of heat developed 

 in them is four times as great as in the two-wire sys- 

 tem, since their capacity for heat is reduced to one- 

 fourth. In the case of conductors reduced one-half 

 in size, the rise of temperature would be the same as 



J Nature, vol. xxiv. p. 489; American engineer, Nov. 7, 1884. 



with the two-wire plan, since the energy expended 

 in heating them is one-half, and their thermal capacity 

 is also one-half. We have supposed, in the calculated 

 economy, that the three wires are all of the same size. 

 Their combined cross-section would then be \ . \ — f 

 of the combined cross-section of the two wires in 

 the first plan. The saving in interest on conductors 

 would then be 25%. Edison sacrifices running-ex- 

 penses in order to diminish the size of his conductors 

 beyond what is clearly the most economical arrange- 

 ment. We take it for granted that the principle of 

 making loss by heat-waste in conductors equal to 

 interest on their first cost was taken into account in 

 calculating the size of conductors in the two-wire 

 plan. H. S. Caehabt. 



Evanston, 111., Dec. 1. 



CAN GHOSTS BE INVESTIGATED? 



In the last number of Science, Mr. G-urney, 

 honorary secretary of the Society for psj'chical 

 research, replies to my paper in Science of Oct. 

 17, 1884. To one whose experience has been 

 that scientific discussion is often nugatory be- 

 cause the parties sedulously refuse to under- 

 stand each other, it is a great pleasure to read 

 Mr. Gurney's paper. The reader who com- 

 pares it with my own, will, I think, have a fair 

 view of the two sides of the question from the 

 special point of view which we have heretofore 

 taken. I therefore ask permission to consider 

 the subject from a somewhat different stand- 

 point. 



When one adduces evidence in favor of telep- 

 athy between living persons, each having the 

 other in mind, I am prepared to listen in the 

 spirit of one who feels that there may be many 

 things on earth not yet dreamed of in our 

 philosophy. But when an imposing array of 

 evidence is presented, tending to show telep- 

 athy between a live man and a dead one, I 

 must frankly confess that I cannot help receiv- 

 ing it in the spirit of the African monarch of 

 whom the following stoiy is told. He had 

 captured a Dutchman who had been trespass- 

 ing on his territory, and was about to put him 

 to death. The prisoner, however, like the 

 heroine of the 'Arabian nights,' managed to 

 postpone the fatal day from time to time by 

 inventing stories about the wonders of civili- 

 zation with which to regale the royal mind. 

 When his inventive powers had reached their 

 limit, he felt obliged to fall back upon facts, 



