282 



SCIENCE. 



[Vol. XII. No. 306 



locomotives as the average of all conditions of track as affected by 

 weather and use. 



3. The possibility of dispensing with the complicated methods of 

 insulation that are necessary and most expensive features of high- 

 potential systems. 



4. A potent cause of the economical working of electric railways 

 is found in the capacity for instantaneous adjustment of the current 

 to demands made upon it. This is so marked in the case of a 

 double-track road with the same number of trains moving in both 

 directions, and all deriving their power from a common generating- 

 station, as to prompt Dr. C. A. Siemens to draw this striking anal- 

 ogy. He declares that two trains on the same track, one descend- 

 ing and the other ascending a gradient, are in as absolute connection 

 by the current in the rails as if tied together by an actual rope. 

 The counter-current generated by the free revolution of the dynamo 

 of the descending train re-enforces the main current, and thus helps 

 the ascending. The result of this is that the maximum capacity of 

 the generating-station need only equal the average work of one 

 motor multiplied by their total number. This will always prove 

 sufficient. Every steam-locomotive must be ready at all times to 

 exert its full power ; and the waste of this, in the aggregate, is 

 enormous. 



familiar steam-engine, which has profited by eighty years of use, 

 experiment, and analysis by the best human ingenuity. 



To resort to generalization, the steam-engine's characteristic 

 function is to transform heat into mechanical work ; and the labor 

 and thought of three generations have only succeeded in recover- 

 ing, in the shape of work, from ten to twenty per cent of the total 

 heat applied to it. The peculiar office of the dynamo-electric ma- 

 chine is the conversion of mechanical work into current electricity ; 

 and in the first decade of its useful existence it returns, in the form 

 of electrical current, ninety per cent of the mechanical work ap- 

 plied to it. The adept steam-engine attains one-tenth of its possible 

 efficiency ; the tyro dynamo-electric machine, nine-tenths. " If 

 they do these things in a green tree, what shall be done in the dry ?" 



ELECTRICAL POWER-DISTRIBUTION. 



One of M. Victor Popp's friends was recently describing with 

 post-prandial eloquence the wonderful system of compressed-air 

 distribution now so extensively operated in Paris. As if it were 

 not marvellous enough to picture to his hearers' minds pneumatic 

 clocks throughout Paris, and all sorts of machinery deriving power 

 from a central station for compressing air, the interesting ' diner- 



The following facts are significant as regards electrical propul- 

 sion : I. The production, by modern stationary engines of the 

 highest efficiency, of a horse-power for two pounds of coal, or less, 

 per hour; 2. A recovery, in kind, from an electric circuit of reason- 

 able length, of at least sixty-five per cent of the mechanical power 

 applied to it ; 3. The consumption by small stationary and locomo- 

 tive engines of from seven to nine pounds of coal per horse-power 

 per hour ; 4. The consequent development in the circuit of a horse- 

 power for three pounds of coal as opposed to seven or nine ; 5. A 

 marked reduction in original and current cost of motive power, due 

 to lessened weight, simplicity, and diminished attendance ; 6. A 

 notably lower rate of deterioration than other machinery, due to the 

 use of low-potential currents, absence of reciprocatory motion, etc.; 

 7. Conservation of permanent way, arising from the lessened 

 weight of motor due to superior natural adhesion and the power of 

 increasing the same magnetically to any necessary degree ; 8. A 

 unique economy arising from the fact that there is no necessity of 

 having superfluous power in reserve, — a consequence of the ca- 

 pacity for instantaneous adjustment of a current throughout an 

 entire circuit to the demands made upon it. 



If one may judge by comparison with other mechanisms, the 

 future of the dynamo-electric motor is pregnant with possibilities. 

 The measure of perfection of any machine is the degree of efficiency 

 with which it performs its specific work. Referred to such a cri- 

 terion, dynamo-electric machinery stands, at the very starting-post 

 of its career, infinitely nearer to its theoretical ultimate than the 



out ' added with a most graceful gesture, " Why, messieurs, with 

 the Popp system you freeze the dead bodies in the morgue, and 

 you cremate them in Pere la -Chaise." And thus the idea is con- 

 tinually forced upon one's mind that this is an age of centralization 

 in the supply of heat, water, light, and power, and, in fine, every- 

 thing that makes life more comfortable, and business more prac- 

 ticable. The application of electricity to the distribution of power 

 has been developed with comparatively more marked progress than 

 the electric-lighting industry met with in the early stages of its 

 existence ; and this is not strange, when we consider the advan- 

 tages of electric motors, and the fact that their use makes a mate- 

 rial difference with small manufacturers in the item of cost of 

 power, besides constituting an important feature of safety. The 

 fact that the noisy, dusty, and dangerous steam-engines which are 

 being used in so many printing-olBces, book-binderies, and various 

 other shops where power is needed, may be displaced by quiet- 

 running electric motors, which are not dangerous and do not take 

 up much room, added to the actual saving in money which is ac- 

 complished by such a change, are points which are so easy of 

 demonstration, and commend themselves so readily to the popular 

 mind, that the introduction of electric motors has not met with any 

 serious obstacles. Although the first experimenters built motors 

 before they built dynamos, it is only within the last two or three 

 years that practical machines of a high efficiency have been offered 

 to the public. Some of the machines now give an efficiency of 

 over ninety per cent in the conversion of electrical into mechanical 



