42 M. Arago on Double Stars* 



are thus then again led, by the simple consideration of proba- 

 bilities, to conclude, that the stars which approximate to each 

 other, do so, not only in appearance, that is to say, not only ac- 

 cording to the laws of perspective or of optics, but, on the other 

 hand, that they really form individual systems. 



I. Some Observations on a Note of M, A. Van BeeJc, purporting 

 to point out an Error in the Bakerian Lecture of the late Sir 

 Humphrey Davy *' On the Relation of Electrical and Che- 

 mical Changes y II. Some Observations on Euchlorine, re- 

 lative to the Question of its Decomposition. By John Davy, 

 M.D., F.R.S., Assistant Inspector of Army Hospitals. Com- 

 municated by the Apthor through Sir James Macgrigor. 



The Note referred to above, occurs in a paper of M. Van 

 Beek, pubhshed in the 38th volume of the Annales de Chimie 

 et de Physique, and is as follows : — 



" Dans le cours de mes experiences sur la preservation des 

 metaux, je me suis aperc^u d'une erreur grave que le celebre 

 chemiste Anglais Sir Humphrey Davy a commise, dans le 

 Bakerian lecture du 8 Juin 1826, ' On the relation of Electri- 

 cal and Chemical Changes,' public dans les Transactions Philo- 

 sophiques de 1826: il recommande d'employer le zinc ou Vetain 

 pour la preservation des chaudieres a vapeur, surtout celles des 

 bateaux a vapeur ou Ton fait souvent usage de Peau de mer. 



" Des experiences decisives m'ont appris que Tetain, bien loin 

 de preserver le fer, est au contraire preserve par ce dernier 

 metal, et qu'ainsi un morceau d'etain introduit dans le chaudiere, 

 au lieu de preserver le fer de Toxidation et de diminuer par la 

 les dangers d'explosion, devrait puissamraent contribuer a sa 

 prompte destruction. 



" Si Ton veut faire usage de cette application utile du prin- 

 cipe de la preservation reciproque des metaux, le zinc seul devra 

 etre employe/' 



This statement is made so strongly by M. Van Beek, that 

 the majority of those who have read it, have probably been in- 

 clined to receive it as correct. Such at least was the impression 

 on my own mind, on a hasty perusal. But when I reflected on 



