Intelligence and Miscellaneous Articles. 317 



and it seems to require that the coast-line along which this littoral 

 fauna flourished stretched round from Scandinavia so as to approach 

 the south-eastern corner of Ireland, while deeper-water conditions 

 co-existed in Wales and England. Volcanic activity began about 

 the period of the accumulation of the Dicranograptus-shales near 

 Tramore, and possibly earlier at Raheen, where it also continued 

 till after the Orthis argentea-he&s had been deposited. 



XXXV. Intelligence and Miscellaneous Articles. 



NOTES ON THE ZEEMAN EFFECT. BY H. M. REESE. 



rPHE work has been confined to a comparatively exhaustive study 

 -*- of the iron spectrum between wave-lengths 3400 and 4500, 

 and of the spectra of magnesium, cadmium, and zinc. The spectra 

 Were obtained by a concave grating of 15,000 lines per inch, 11 

 feet radius. Photographs were taken of the effect as seen when 

 viewed across the field of force, and also in the case of iron, as 

 seen along the field. The time of exposure varied from fifteen 

 minutes to one hour and a half, according to the region in the 

 spectrum and the brightness of the lines. 



In the case of iron, the intensity of the field used is unknown 

 for the reason that the introduction of an iron terminal to get the 

 spark seriously disturbs the field ; and it is impracticable to make the 

 measurement with the terminal in position. With the exception 

 of the cases of reversed polarization discovered last year, all the 

 iron lines examined appeared as plane triplets of the usual type when 

 viewed across the field, or as quadruplets, or else were apparently 

 unaffected. There are four quadruplets, viz., the lines 3466-6, 

 3475-6, 3490-7, and 3587-13. In the case of 3466-0 and 3475-6, a 

 Nicol's prism was used, which showed that in each case the inside 

 pair of components was due to vibrations along the field, the outer 

 pair to vibrations across the field. In physical character the four 

 lines differ somewhat. In 3466*0 the middle pair of components 

 are five or six times as intense as the outer pair and are not very 

 sharp, while the space between the inner pair is considerably 

 greater than that between either member of this pair and the out- 

 side component adjacent to it. The other three quadruplets are 

 more uniform in intensity ; and their components are more 

 uniformly spaced ; further, all are quite sharp though rather faint. 

 All four are, so far as I can judge, symmetrical as regards intensity, 

 and probably also as regards spacing ; but the most careful 

 measurements that I could make indicated a possibility that in the 

 case of 3466-0 the mean of the inner pair is a trifle farther 

 toward the red than that of the outer pair. The separation of the 

 outer pair in the several cases is -76 Angstrom unit for 3466*0, 

 •50 for 3475-6, -48 for 3490-7, and -40 for 3587-13. In this same 

 region the triplet 34769 is worthy of mention here because of 

 the very wide separation, -72 Angstrom unit, between its lateral 

 components ; the same measurement in other triplets of the region 

 varying from -39 down to a mere broadening. It is rather re- 

 markable that so many lines of an unusual character should occur 



