﻿certain Spectral Lines oj Zinc and Titanium. 399- 



the mean error in measurement. For each line always the 

 same standard iron lines were used. 



The tables which are given below contain the results of 

 the measurements of seven lines of the zinc spectra and 

 thirteen lines of the titanium spectra. The first column 

 contains the wave-lengths obtained in the arc by using pure 

 metal electrodes and a current of 4 amperes. In the re- 

 maining columns the decimal of the wave-length is given 

 which was obtained under the conditions stated at the head 

 of the column. The numbers in brackets ( ) represent the 

 intensities of the lines valued from 1 to 100, the greater 

 number corresponding to the greater brightness. R means 

 that the line is reversed, and n that it is not sharp. The 

 wave-lengths obtained by Exner and Haschek are given in 

 the last two columns of each table for comparison. Their 

 scale of intensity is from 1 to 1000, u means the line is- 

 reversed, and + that it is not sharp. 



Zinc. 



Tables I. and II. contain the measurements obtained for 

 the zinc lines. 



The zinc which was used for the electrodes was the 

 chemically pure zinc of commerce. For the spark the 

 electrodes were about 2' 5 cm. long, and 0*5 sq. cm. cross- 

 sectional area with chisel-shaped edges, which were placed 

 parallel to each other. The spark was vertical and parallel 

 to the slit. Many photographs were taken of the spark 

 spectra in the region of the lines chosen for examination, the 

 time of exposure of the plate being varied from 2 seconds to 

 3 minutes. In this manner some plates were obtained having 

 strong broad lines and others with sharply defined lines. 

 Photographs of the arc spectra of zinc were also obtained, 

 but some difficulty was experienced, owing to the lower elec- 

 trode melting and falling away. This was avoided by melting 

 some zinc into a small carbon cup and using this as the 

 lower electrode. In order to ascertain the effect on the wave- 

 lengths of the lines caused by alteration of the strength of 

 the current in the arc, photographs of the spectra were taken 

 when the current had various strengths between 4 and 18 

 amperes, the time and exposure being kept constant. In 

 order to obtain lines of various intensities photographs were 

 taken also when the time of exposure was varied. It was 

 difficult to obtain weak but sharp zinc linos owing to the 

 short exposure necessary, consequently part of the Schumann 

 condenser was cut off by a screen, and thus only some of the 

 light was allowed access to the slit. 



