58 THE POPULAR SCIENCE MONTHLY. 



ing influence caused by charge in under-ground or submarine conduct- 

 ors. These conditions are particularly favorable to under-ground line 

 wires, which possess other important advantages over the still prevail- 

 ing over-ground system, in that they are unaffected by atmospheric 

 electricity, or by snow-storms and heavy gales, which at not very rare 

 intervals of time put us back to pre-telegraphic days, when the letter- 

 carrier was our swiftest messenger. 



The under-ground system of telegraphs, first introduced into Ger- 

 many by Werner Siemens in the years 1847-'48, had to yield for a 

 time to the over-ground system owing to technical difficulties, but it 

 has been again resorted to within the last four years, and multiple land 

 cables of solid construction now connect all the important towns of 

 that country. The first cost of such a system is no doubt considerable 

 (being about 38 per kilometre of conductor as against 8 10s. the cost 

 of land lines) ; but, as the under-ground wires are exempt from frequent 

 repairs and renewals, and as they insure continuity of service, they are 

 decidedly the cheaper and better in the end. The experience afforded 

 by the early introduction of the under-ground system in Germany was 

 not, however, without its beneficial results, as it brought to light the 

 phenomena of lateral induction, and of faults in the insulating coating, 

 matters which had to be understood before submarine telegraphy could 

 be attempted with any reasonable prospect of success. 



Regarding the transmission of power to a distance, the electric cur- 

 rent has now entered the lists in competition with compressed air, the 

 hydraulic accumulator, and the quick-running rope as used at Schaff- 

 hausen to utilize the power of the Rhine-fall. The transformation of 

 electrical into mechanical energy can be accomplished with no further 

 loss than is due to such incidental causes as friction and the heating of 

 wires ; these in a properly designed dynamo-electric machine do not 

 exceed 10 per cent, as shown by Dr. John Hopkinson, and, judging 

 from recent experiments of my own, a still nearer approach to ultimate 

 perfection is attainable. Adhering, however, to Dr. Hopkinson's de- 

 termination for safety's sake, and assuming the same percentage in 

 reconverting the current into mechanical effect, a total loss of 19 

 per cent results. To this loss must be added that through electrical 

 resistance in the connecting line wires, which depends upon their 

 length and conductivity, and that due to heating by friction of the 

 working parts of the machine. Taking these as being equal to the 

 internal losses incurred in the double process of conversion, there re- 

 mains a useful effect of 100 38 = 62 per cent, attainable at a distance, 

 which agrees with experimental results, although in actual practice it 

 would not be safe at present to expect more than 50 per cent of ulti- 

 mate usefid effect, to allow for all mechanical losses. 



In using compressed air or water for the transmission of power, the 

 loss can not be taken at less than 50 per cent, and as it depends upon 

 fluid resistance it increases with distance more rapidly than in the case 



