1895.] On the new Gases obtained from Uraninite. 5 



on May 4. The observations were made by Mr. Fowler, in the third 

 order spectrum of a grating having 14438 lines to the inch, and the 

 observing telescope was fitted with a high power micrometer eye- 

 piece ; the dispersion was sufficient to easily show the difference of 

 position of the D 3 line on the east and west limbs, due to the sun's rota- 

 tion. Observations of the chromosphere were therefore confined to 

 the poles. 



During the short time that the tube retained its great brilliancy, 

 a faint line, a little less refrangible than the bright yellow one, and 

 making a close double with it, was readily seen ; but afterwards a 

 sudden change took place, and the lines almost faded away. While 

 the gas line was brilliant, it was found to be " the least trace more 

 refrangible than D 3 , about the thickness of the line itself, which was 

 but narrow " (* Observatory Note-book '). The sudden diminution in 

 the brightness of the lines made subsequent observations less certain, 

 but the instrumental conditions being slightly varied, it was thought 

 that the gas line was probably less refrangible than the D 3 line by 

 about the same amount that the first observation showed it to be 

 more refrangible. Giving the observations equal weight, the gas line 

 would thus appear to be probably coincident with the middle of the 

 chromospheric line, but if extra weight be given to the first obser- 

 vation, made under much more favourable conditions, the gas line 

 would be slightly more refrangible than the middle of the chromo- 

 sphere line. 



Pressure of other work did not permit the continuation of the 

 comparisons. In the meantime, Runge and Paschen announced* 

 that they also had seen the yellow line of the cleveite gas to be a 

 close double, neither component having exactly the same wave-length 

 as D 3 , according to Rowland. 



They give the wave-length of the brightest component as 5878*883., 

 and the distance apart of the lines as 0*323. 



This independent confirmation of the duplicity of the gas line led 

 me to carefully re-observe the D 3 line in the chromosphere for 

 evidences of doubling. On June 14 observations were made by 

 Mr. Shackleton and myself of the D 3 line in the 3rd and 4th order 

 spectra under favourable conditions ; " the line was seen best in the 

 4th order, on an extension of the chromosphere or prominence on the 

 north-east limb of the sun. The D 3 line was seen very well, having 

 every appearance of being double, with a faint component on the red 

 side, dimming away gradually ; the line of demarcation between the 

 components was not well marked, but it was seen better in the 

 prominence than anywhere else on the limb." (' Observatory Note 

 Book.') 



It became clear, then, that the middle of the chromosphere line, as 

 * « Nature,' vol. 52, p. 128. 



