66 



Mr. H. Hilton o/i the GrapJdcal 



parallel to the five lines for barium, strontium, and calcium 

 given as examples, but the whole ten lines exhibit a slight 

 convergence towards the same point. 



Taking now the other mode of correspondence mentioned 

 first, which is illustrated by the homology of the triplets (and 

 many other lines) in the spectra of zinc and cadmium, we 

 find the following connexion between the spectra of radium, 

 mercury, and barium. 



Lines meetino- on the Line of Zero Atomic AV'eio-ht at 

 Oscillation-Frequency of about 44610. 



Radium .... 26207-7 (16) and Barium .... 37940-1 (8) 

 Radium .... 20714-8 (10) and Barium .... 35892-6 (Sn) 

 give 22o'05 for the atomic weight of Radium. 



Lines meetino- on the Line of Zero Atomic Weight at 



Oscillation-Frequency 52450. 



Radium 



give 223-47. 

 Radium 



give 220 36. 

 Radium 



give 223-13. 

 Radium 



give 227-39. 

 Radium 



17195-5 and Mercury 



26207-7 (16) 



26207-7 (16) and Mercury 

 27393-7 



17195-5 

 27393-7 



and Mercury 



21149-7 and Mercury 



26207-7 (16) 



. 26207-7 (IC) and Mercury.. 

 21350-9 (14) 

 give 224-63. 



The mean of all these results is 224*89. 

 of radium as determined by Madame Curie is 225. 



24703-6 (6;-) 

 31921-9 (8;-) 



, . 31921-9 (8r) 

 32898-8 {47i) 



. 24703-6 {6r) 

 32898-8 (472) 



. 31982-2 (10;-) 

 28069-2 (4m) 



. 31919-3 (8r) 

 28069-2 (4ji) 



The atomic weio-ht 



- IX. On the Graphical Solution of Astronomical Problems. 

 By Haeold Hiltox *. 



IT is proposed in this paper to give a brief description of 

 the use of the stereographic projection in the graphical 

 solution of astronomical and other problems. In this projec- 

 tion points and lines on a sphere are projected on the plane 

 (A) of a great circle from either of its poles P and Q. It is 

 usual to project from P points on the sides of h remote from P^ 

 and from Q points on the side of h remote from Q ; marking 

 the points with a cross ( x ) in the first case, and with a little 

 circle (o) in the second. In this way all points of the sphere 

 are projected into points lying within the great circle s in 



* Comaiunicated by the Author. 



