86 I. W. and A. Dupré on the existence of a 
Mr. Pepys’s gigantic single galvanic pair at the London Institu- 
tion—cones of mercury rose over the general level of the fluid 
and above the polar wires*. Even Mr. Faraday has failed in re- 
peating the experiment, which is remarkable since, though he 
only used 100 pairs, the electromotive power of modern batteries 
vastly exceeds that of those used in Davy’s time, and the suc- 
cess with Pepys’s apparatus shows that intensity is not indispen- 
sablet. Mr. Faraday thinks that Davy’s cones and Ampeére’s 
repulsion experiment are due to one and the same cause. But 
T incline to believe that Davy’s cones intimate an attraction, and 
not repulsion, and so far concur with the results of my experi- 
ments with the torsion-balance. 
I have had Davy’s apparatus constructed and placed in the 
Natural Philosophy Class Collection in Edinburgh, where I hope 
that it may one day be tested with an adequate power. 
Pitlochry, N. B., 
July 11, 1860. 
Postscript. —Soonafter writing the preceding notice, Irequested — 
Professor A. De la Rive to give me any confirmation which his 
memory could supply, of the success of Ampére’s experiment ; 
and this he has kindly done with all the precision which might 
be expected from him. He adds that the motion could not be 
due to the action of the earth’s magnetism, as it was independent 
of the direction of the current. 
United College, St. Andrews, 
November 26, 1860. 
22 January 1861.—I have just learned from Professor Tait 
that he has succeeded in repeating Ampére’s experiment. 
XIII. On the existence of a Fourth Member of the Calcium group 
of Metals. By F. W. and A. Durret. 
URING our recent examination of London waters by the 
beautiful method of Kirchhoff and Bunsen, we several times 
noticed a faint biue line not due to strontium or potassium, or to 
the lately discovered cesium. Having since worked with larger 
quantities of the deep well-water which had given this line most 
distinctly, we believe we are now justified in stating that the 
group of calcium, strontium, and barium, like that of the alkali- 
metals, contains a fourth member. ‘This new metal gives but 
* Sir H. Davy in Philosophical Transactions for 1823. Compare Mr. 
Faraday’s ‘ Researches m Electricity,’ Ninth and Thirteenth series, arts.1113 
and 1609. 
+ Mr. Faraday’s ‘ Researches,’ as above cited. 
{ Communicated by the Authors. 
i ee 
aT a os “ 
