24 



THK .VRsOKITION' AM) KMISSIOX OK .\IK. 



OP" THE LIMIT Ol' Tllp; K.NOWN IIYOROGEX SPECTRUM. 



I have been able to follow the hydrof;en spectnini for about 6- beyond the last 

 of the spectral series of Plates I-III ; but hitherto not with sufficient clearue,ss 

 f(jp reproduction. The most peifect of my photographs of this region (No. 4222) 

 is not cleai'ly enough defined to bear a twenty-fold enlargement. Accordingly, they 

 may here receive a merely verbal treatment. At first, with all my pains, I was able 

 only to secure traces of some blurred lines. It was not until I interchanged the 



