410 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



menters, by a bolometric method and a calorimetric method respectively, 

 have measured the resistance of the spark in air between solid metallic 

 terminals. For a proper comparison we should take the resistance for 

 those spark-lengths that require the same potential to start the discharge 

 as is required by the mercury interrupter (7070 volts). 



TABLE VII. 

 Resistance of Spark. R. Lindemann. 



TABLE VIII. 

 Resistance of Spark. Battelli and Magri. 



Among the results given by Lindemann only the fourth value of 

 Table VII. is appropriate for these comparisons. Lindeinanu's value is 



