58 Royal Society. 



phj'." By Charles Brooke, M.B., F.R.C.S.E. Communicated by 

 G. B. Airy, Esq., F.R.S., Astronomer Royal. 



Tlie author enters into fuller details than he had done in his 

 former communication to the Society, which was read on the 18th 

 of June, respecting the construction of the instrument, the prepa- 

 ration of the highly sensitive photographic paper employed in the 

 process, and the minute adjustments necessary for ensuring accuracy 

 in registering the results. 



In a supplement to the above paper, the author describes the 

 methods he has contrived for obtaining a similar automatic registra- 

 tion of the heights of the barometer and thermometer, by suitable 

 additions to the same apparatus which registers the magnetic varia- 

 tions. 



W. R. Grove, Esq., M.A., F.R.S., delivered the Bakerian Lecture 

 — " On certain Phenomena of Voltaic Ignition, and on the Decompo- 

 sition of Water into its constituent Gases by heat." 



Tlie author refers to an eudiometer, an account of which was 

 published by him in the ' Philosophical Magazine' for 1840, formed 

 of a glass tube, into the closed extremity of which a loop of plati- 

 num wire was sealed. The gases to be analysed were mixed in this 

 tube with a given volume of oxygen and hydrogen, and detonated 

 or slowly combined by tlie voltaic ignition of the platinum wire. 

 He was thence led to try a further set of experiments on the analysis, 

 by this instrument, of such gases and vapours as are decomposable 

 by heat; the process being capable of much greater exactness than 

 the received one of passing them through ignited tubes. The re- 

 sults of the analyses of several gases by this means are given in the 

 paper. When carbonic acid and hydrogen are mixed in equal 

 volumes and exposed to the ignited wire, the hydrogen abstracts 

 oxygen from the carbonic acid, and leaves carbonic oxide. Con- 

 versely, when carbonic oxide is exposed over water to the ignited 

 wire, it abstracts oxygen from the aqueous vapour, and forms car- 

 bonic acid. 



It thus apjieared, that provided there were bodies present capable 

 of absorbing by affinity the elements of water, ignited platinum 

 would either compose or decompose water. The author was thence 

 led to hope that he might by ignited platinum decompose water into 

 its constituents, without absorption by other bodies, and thus pro- 

 duce converse effects to those already known. In this he ultimately 

 succeeded by various methods, in some of which the ignition was 

 produced by electrical means ; in others by ordinary calorific pro- 

 cesses, such as the oxyiiydrogen blowpipe, &c. 



A platinum wire is ignited at the closed extremity of a species of 

 tube retort, full of pure water, and having a narrowed neck close 

 above the wire ; as soon as the wire becomes incandescent, it forms 

 around itself an atmosphere of vapour which it immediately decora- 

 poses ; a natural valve being formed by the conflict of ascending 

 gas and descending water, the bubbles of mixed gas are cut off by 

 an intermittent action, and thus, as their recombination is prevented, 

 a volume of gas collects in the bend of the tube and is ultimately 



