( 548 ) 



RUBIDIUM. 



CAKSIUM. 



MERCURY. 



* The intensity of the green and yellow mercury lines has been put = 10. 



Mathematics. — "On the locus of the pairs of common points and 

 the envelope of the common chords of the curves of three 

 pencils." 2 nd part. : Application to pencils of conks. By Dr. 

 F. Schuh. (Communicated by Prof. P. H. Schoute.) 

 (Communicated in the meeting of December 29, 1906). 



9. If the pencils of curves are pencils of conies (r = s = t = 2) 

 then in the case of there being no common base-points the locus is 

 of order fifteen and the envelope of class six. In the following we 



