2 B. E. Moore e 
ton’s law, and therefore the magnetic separation may be used to 
establish series. In fact, Runge suggested this possibility, and 
applied it in barium where no series had been discovered. He 
found that barium gave representatives of series, but not in suff- 
cient number to establish series. 
The following experiments propose to use this inverse method, — 
firstly in a more complete study of barium, and then in other 
substances wherein no series have been found, to see if a series 
relationship can be established in any of the different types of 
magnetic separation. 
Il. EXPERIMENTAL METHOD 
The spectral lines were photographed by means of a 21-foot 
concave grating with fixed circular camera. The light consisted 
of a spark of the substance which had been dried upon thin car- 
bon plates and so placed in a strong magnetic field that the spark 
was parallel to the lines of force.t Owing to the varying intensity 
‘of the different lines, photographs were taken with different times 
of exposure, varying from fifteen minutes to two hours in the 
violet and up to six hours in the red. The photographs were all 
taken with the pole pieces at the same distance apart, so that by 
varying the current on the electromagnetic circuit one could ob- 
tain ad libitum any field strength up to the maximum of 24,400 
lines per sq. cm. The field strength was determined from re- 
peated measurements of the separation of calcium line 396836, - 
which occurs as an impurity in the carbon electrode, and from a 
few special photographs of zinc line 4680, assuming Runge’s 
measurements for these lines at 21,000 C. G. S. units to be cor- 
rect. All calculations are given at the above maximum field 
strength. Other field strengths were used to determine the true 
components of lines very close together or to obtain readings for 
overlapping components. Frequently such lines are determined 
from the distance of the one free component from the undisturbed 
*Many substances adhere so well to carbon that the writer thinks this. 
plan, together with the circular camera, will make it possible to photo- 
graph some of the promising costly substances: 
24 
