373 
1907-8.] Note on Electrical Resistance of Spark Gaps. 
given in the table were obtained with this break. In place of the thermo- 
couple a quadrant electrometer with uncharged needle was connected to the 
plates of the resonator condenser, but was not so convenient to work. 
Zinc always gave a larger decrement when freshly cleaned, but cleaning 
had no definite effect on the others. When the Wehnelt interrupter was 
used much lower values of the decrement were obtained, 0T2 and there- 
abouts. 
The decrease of the decrement with increase in the length of the spark 
gap in the case of aluminium and nickel is very striking. Drude has 
shown in the case of zinc that as the length of the spark gap increases the 
decrement decreases to a minimum and then increases again, and the 
minima in the case of aluminium and nickel probably lie beyond the range 
that could be investigated with the means at my disposal. 
The measurements were made in the Physical Laboratory of the 
University of Glasgow. 
( Issued separately July 20 , 1908 .) 
