103 
Ordinary Meeting, April 7th, 1863. 
E. W. Binney, F.R.S., F.G.S., President, in the Chair. 
Mr. Edmund Salis Schwabe, B.A., was elected an Ordinary 
Member of the Society. 
Messrs. Robert Worthington and G. V. Vernon were 
appointed Auditors of the Society’s Accounts for the present 
Session. 
Mr. Brothers exhibited and described an apparatus for 
determining the magnitudes of stars. (See Proceedings of 
Physical Section for April 2nd.) 
Professor Roscoe communicated the following extract from 
a letter he had just received from Professor Bunsen, respecting 
the atomic weight of c cesium. Professor Bunsen formerly 
found the atomic weight of this metal to he 123; since then, 
Messrs. Johnson and Allen, Yale College, United States, 
found, by operating on large quantities, the number to be 133. 
He writes, “The atomic weight Cs.=133 is quite right. The 
difference is caused by an error of about one per cent on the 
chlorine contained in the chloride of caesium, owing to an 
amount of impurity which cannot be separated according to 
the method I first used for purification. I have employed all 
the three grammes of Cl Cs, with which I was obliged to 
make the whole of the investigation of the caesium compounds 
for another determination of the atomic weight of the metal, 
and I find the same number (133) as the Americans found, 
hut by quite a different method. The alteration from 123 to 
133 makes a difference in the analysis of most of the 
salts, of from a quarter to one per cent in the percentage 
composition.” 
Proceedings — Lit, and Phil. Society— No. 12 .— Session 1802 - 3 . 
