402 



the theory still further, Dulong attempted, by reversing the process 

 of Laplace, to deduce the coefficient by which the Newtonian for- 

 mula is to be multiplied, directly from experiments themselves. The 

 object of the present paper is to compare the investigation of Dulong 

 with the experiments on the velocity of sound made by Drs. Moll 

 and Van Beek, of which an account was lately published in the Phi- 

 losopliical Transactions. By applying the values of the coefficients 

 thus obtained, the computed velocities of sound came out much nearer 

 to the observed velocities ; and the author concludes by remarking, 

 that such differences as yet remain between calculation and experi- 

 ment, may with great probability be ascribed to the errors, which are 

 unavoidable in observations of so complicated a nature. 



On the Elasticity of Threads of Glass, with some of the most useful 

 Applications of this property to Torsion Balances. By William 

 Ritchie, A.M. F.R.S., Rector of the Royal Academy of Tain. Read 

 March 18, 1830. [Phil. Trans. 1830, p. 215.] 



The author proposes the employment of threads of glass in the 

 construction of torsion-balances, in place of the silver wire, used by 

 Coulomb for the measurement of minute electric or magnetic forces. 

 He describes a galvanometer of his invention, acting upon this prin- 

 ciple, the intensity of the galvanic current being measured by the 

 torsion of a slender filament of glass, to the lower end of which a 

 magnetized needle is fixed at right angles. He also applies the same 

 power to the improvement of the sensibility of the common balance 

 for weighing minute bodies, by affixing to the beam a long glass 

 thread horizontally in the axis of suspension, by the torsion of which, 

 when the balance has been brought nearly to a level, the more accu- 

 rate adjustments are to be effected. On the whole he considers 

 that glass, from its perfect elasticity, possesses decided advantages 

 over metallic wires, for the construction of instruments acting on the 

 principle of torsion. 



Memoir on the occurrence of Iodine and Bromine in certain Mineral 

 Waters of South Britain. By Charles Daubeny, M.D. F.R.S. 

 Professor of Chemistry in the University of Oxford. Read May 6, 

 1830. [PA/7. Trans. 1830, p. 223.] 



The author lays claim to being the first who announced to the 

 public the existence of bromine in the mineral springs of England ; 

 a discovery similar to that which had been previously made by others 

 in many analogous situations on the Continent. His reason for offer- 

 ing the present communication to the Royal Society is, that he has 

 examined on the spot a great number of mineral springs, and en- 

 deavoured to obtain, wherever it was practicable, an approximation 

 to the proportion which iodine and bromine bear to the other ingre- 

 dients. He has also aimed at forming an estimate of their compara- 

 tive frequency and abundance in the several rock formations, an ob- 



