464 Mr. H. Smith : Spectroscopic Study of the Electric 



insertion of a spark-gap diminished the number of dots but 

 increased their brightness. As the spark-gap was lengthened 

 the dots in a series diminished still farther in number till 

 there was but one very brilliant one. The number of these 

 dots in a series gave the number of times the condenser 

 discharged through the brush per half alternation of the 

 current. 



An image of the brush, or of the discharge in the capillary* 

 was focussed upon the slit of a Hilger fixed-arm spectro- 

 graph. The limits of the spectrum obtained lay between 

 about \ = 6700 A and \=4200 A. Photographs were taken 

 for different liquids, points and capillaries being used of 

 various diameters. The electrical conditions were varied as 

 much as possible. The general arrangement of the apparatus 

 is shown in fio-. 3. 



Fiff. 3. 



SLH OF SPEC TRCH.ftflPH' 



GALVANOMETER 



An attempt was made to correlate the results with the 

 electrical conditions of the discharge. For this purpose the 

 current was measured with a type of hot-wire ammeter often 

 used for high-frequency current measurements in wireless 

 telegraphy. A .single strand of very fine platinum wire was 

 stretched across the junction of a copper-constantan thermo- 

 couple made of very fine wires. The platinum wire was in 

 series with the cell, the thermocouple in series with a suitable 

 galvanometer. The heating effect of the platinum wire at 

 the junction was sufficient to produce a current in the 

 thermocouple circuit which would give measurable deflexions 

 on the galvanometer scale. The coil of the galvanometer 



