Minutes of Proceedings. 339 



were modified in other ways. He communicated the results to the 

 Eoyal Dublin Society in December, 1897, and he exhibited photo- 

 graphs of the triplets and quartets, displaying the close analogy 

 between certain lines of zinc and of cadmium. In this paper he 

 wrote : — " It is clear, therefore, that the magnetic effect depends not 

 so much on the wave-length of the spectral line as on some 

 hidden quality which we may refer to the character of the line," and 

 "perhaps it might be possible to group the spectral lines of each 

 substance into sets, so that some law of wave-length might apply to 

 the lines of each set." 



In order to study the various types systematically, and in the hope 

 of finding some general law connecting lines of a common type, 

 Preston had an exceedingly powerful electro-magnet constructed, 

 according to an original design. This instrument in every way acted 

 up to his expectations. By its aid he was enabled to extend the 

 classification of the lines, and he enunciated a very important general 

 law. He found the lines of a given spectrum could be grouped insets 

 so that the ratio which the change of wave-length produced by the 

 magnetic force bears to the square of the wave-length is constant for 

 each set, and he found moreover that this ratio is the same for cor- 

 responding sets of lines in the spectra of different substances. He 

 considered this pointed to a composite structure of the chemical ele- 

 ments, and thought it possible that to each type of line corresponded 

 a kind of stuff more simple than the element. 



Dr. Preston's death is a cause of lasting regret to the Academy, 

 and a serious loss to Science. 



It was proposed by Dr. Greenwood Pirn, and seconded by Judge 

 Kane, and adopted — 



That in the event of Her Majesty the Queen being graciously 

 pleased to receive addresses on the occasion of her visit to Ireland, an 

 Address of welcome be presented by the Academy, and that the officers 

 be requested to prepare and submit a draft Address. 



The following draft Address was adopted, on the motion of the 

 Secretary, seconded by the Treasurer. 



