COM PA RA TIVE EXPERIMENTS. 1 1 9 



for a light of 100 Carcel lamps may be taken as between 

 0*92 and i *8o horse-power, and reckoning from the mean of 

 these, i '47 a number very near that found by Heilmann 

 and Ducommun we have 70 Carcel lamps for each horse- 

 power, with a speed cf 850 rotations per minute. According 

 to Tresca's figures this would be 103 lamps, or 1,036 candles. 



According to experiments made with the Jablochkoff 

 candle in Jablochkoft's workshops, the quantity of light per 

 horse-power would be represented by 23 gas-lights for the 

 machines of De Meritens, by 28 or 30 lights for the Gramme 

 machines, and by 30 or 32 lights for the Siemens machines. 



It will be perceived that the real value of these results is 

 by no means agreed upon ; but it must also be admitted that 

 the experiments are very difficult to make on account of the 

 luminous effects, which exhibit considerable differences from 

 one moment to another. 



We must call the reader's attention to one important re- 

 mark that has been made on the results yielded by the 

 machines according as the light is concentrated or divided. 



According to the comparative experiments that have been 

 made, it would appear that a much greater motive power is 

 required to obtain the same light when it is divided among 

 several lamps than when it is concentrated at one point. In 

 the Courrier des Etats Unis of the 28th January, 1879, we 

 read thus : 



Given a light of one lamp equivalent to 15,000 candles, the 

 same quantity of light divided between five lamps inserted in 

 the same circuit will be reduced to 2,000 or 3,000 candles for 

 the same motive power ; in other words, it would be necessary to 

 use five or six times as. much power to produce a divided light 

 as to produce a single light, and this proportion will increase 

 with the number of divisions. If, however, this principle is cor- 

 rect, it will have its counterpart and corrective in that other 

 principle, which also rests on a progressive scale : namely, that 

 by increasing the power generating the electricity beyond what 

 is necessary to produce a certain quantity of light, say 15,000 

 units for a single lamp, the loss by the division of the current 



