444 Mr. T. S. Davies on Geometry and Geometers, 



IfL Bove's Repertorium (vol. viii. p. 273), values of the electro- 

 chemical equivalents of water and zinc, determined by Weber, 

 who was the first to give an electro-chemical equivalent in abso- 

 lute electro-magnetic measure, and by other experimenters, 

 are given in absolute measure according to the French units. 

 To reduce these to British measure, we must multiply by 

 (2*1692), the square mot of the fraction obtained by dividing 

 the number (15*438) of grains in a gramme, by the number 

 (3*2809) of feet in a metre. The electro-chemical equivalent 

 of water is obtained by multiplying that of hydrogen by 9 ; and 

 according to the theory of equivalence in electro-chemistry, 

 it might also be obtained by multiplying the electro-chemical 



9 9 



equivalent of zinc by ooTo > and that of copper by oTT^- The fol- 

 lowing table shows the values of the electro-chemical equivalent 

 of water in British absolute measure obtained in these different 

 ways. 



Observers. 



Galvanometer tised. 



Electro-chemical action 

 observed. 



Deduced electro- 

 chemical equiva- 

 lent of water. 



Weber 



Bunsen ... 

 Biinsen ... 



Casselmann 



Casselmann 

 Jo e 



Joule 



Joule 



The ** electro-dynamometer" 



Tangent galvanometer 



Ditto. 



Ditto. < 



Ditto. I 



Ditto. 



Ditto. 

 Ditto. 



Decomposition of water 

 Decomposition of water 



Dissolution of zinc 



Decomposition of water 

 in acid and saline so- 

 lutions 



Zinc [deposited or dis- 

 solved.-'] 



Decomposition of water 



Deposition of zinc from 



solution of sulphate of 



zinc 



Deposition of copper 

 from solution of sul- 

 phate of copper ... 



•02034 

 •02011 

 •01993 



•02033 



•02021 

 •01981 



•02030 



•02002 



LXVII. Geometry and Geometers. Collected by the late Thomas 

 Stephens Davies, F,R,S,L,^E.^c^^ 



No. VIII. 

 [Contmued from vol. i. p. 544.] 



ONE or two remarks upon points suggested by Professor 

 Rigaud's letter, apart from all considerations about Pappus, 

 Halley, and Porisms, will not be out of place here; viz. upon the 



♦ Communicated by James Cockle, Esq., M.A., Barrister-at-Law, who 

 adds the fallowing note : — 



[" The above manuscript and its accompanying foot-note, both of which 



