42 



THE STRUCTURE OF THE NUCLEUS. 



TABLE i6.— l^ROMISCUOUS COMPARISONS OF AXIAL AND FIELD COLOR (CO- 

 RONAL CENTER) MADE IN THE SINGLE DRUM. 



(l) and (2), exhaustion 76-50 cm. 

 (3), (5). (6) " 76-57 cm. 



(4), " 76-66 cm. 



(6), sunlight aiui yiuund-glass screen. 

 (5)1 (6). punk nuclei. 



Tlie coronal center whicli corresponds to the initial hi lies and blue greens of 

 the table, is not determinable as to color, when seen in the drum ; in the globe, it 

 appeared to be a diffuse red-riramed fog. The first pronounced color contrast 

 which a[)})ears is the orange-red axial color and the blue-green or green-blue field. 

 This is usually easily obtained, and is complementary in character. The axial colors 

 then move toward violet and the field colors toward yellow. After this, the axial 

 colors are already nearly white, or the tinge of color is so faint that it would be 

 IkikI to recognize it, if the color sequences were not known from the steam Jet. 

 Nevertheless the march of axial colors into bluish, greenish, and yellowish tints, 

 corresponds to a inarch of the field from yellows into reds and purjiles. The colors 

 thus follow each other around the circle, apparently, diametrically opposed in 

 position. If the exhaustions are either too large (1/3) or too small (1/6), the 

 colors are less easily recorded than for intermediate cases. 



In none of my experiments were the yellows of the first order, which appear 

 so splendidly in the steam tube, obtained, blue being the first axial color. The 

 endeavor was made to reach these results by placing the phosphoi'us ionizer 

 within the driiiii. The result was unfavorable; ordinary smoke filaments tracing 

 the path of the convection currents appeared. The fii*st exhaustions produced 

 irregular fogs only. Colors did not appear clearly until the 9th exhaustion, and 

 they had then already run into higher orders. 



As the colors of the annuli are projected on the walls of the diiim, ;us in 

 figure 8, their angular value for a fixed position of the eye at e might be read off 

 on an annular scale within the drum. Diffraction of the particles within the axial 



