274 Prof. E. W. Wood on the Existence of 
We must remember that we are observing rotations which 
result from a pair of absorption-bands, which may behave in 
different ways, that is they may conspire for wave-lengths 
on the blue side and oppose each other for the longer waves 
on the red side. If, for example, the stronger band at wave- 
length 5790 gave positive rotations for the red waves, and 
negative rotations for the green, and the fainter band gave 
negative rotations for both red and green, the absence of a 
sharply marked extinction-band on the red side is at once 
explained. Both types of rotation curves are theoretically 
possible according to Drude, according to the fundamental 
hypothesis adopted. The second type is characteristic of 
sodium vapour, as is well known. 
I am now preparing a set of these films for Dr. Bates, of 
the Bureau of Standards, who plans to investigate them with 
a large and very accurate polarimeter. 
XXIII. On the Existence of Positive Electrons in the Sodium 
Atom. By R. W. Wood, Professor of Experimental 
Physics in the Johns Hopkins University *. 
[Plate XIV.] 
THE greater part of the evidence which we have obtained 
thus far regarding the structure of the atom, indicates 
that the centres of vibration which emit the spectral lines 
are negatively charged corpuscles. The positive charges 
appear to be associated with the atom as a whole, and the 
assumption is often made that the positive electrification is 
of uniform distribution. 
The Zeeman effect show r s us that the D lines of sodium are 
due to vibrators carrying negative charges, a fact which is 
true of all other lines which show the effect. That a negative 
charge is associated with the centres of vibration which emit 
the I) lines is also shown by the direction (positive) of the 
magnetic rotation of the plane of polarization, for waves of 
very nearly the same frequency as that of the D lines. As 
is well known band spectra do not show the Zeeman effect at 
all, consequently we are unable to apply this test to the 
investigation of the nature of the charge associated with the 
centres of emission of the lines of which the bands are 
made up. 
Some of the lines which make up the complicated channelled 
* Communicated by the Author. 
