1825.] ' Rx)t^al Society. 145 



In seeking for a method of removing this source of inac- 

 curacy, it occurred to Mr. Daniell that gases were better 

 confined over water than over mercury, on account of the 

 water making a perfect contact with the glass of the jars in 

 which they were contained, which was not the case with the 

 mercury ; and Mr. Faraday furnished him with a case in point, 

 in which a mixture of oxygen and hydrogen confined in bottles 

 over water, and in the dark, for about a twelvemonth, were 

 found unaltered either in nature or in quantity; whilst bottles 

 into which the same mixture had been passed, and confined over 

 mercury, under the same circumstances, were found to contain 

 nothing but common air. Mr. D. thence inferred, that if the 

 tube consisted of some substance which the mercury would 

 wet (if he might be allowed the expression), the insinuation of 

 air would be prevented. In the experiments he made when 

 constructing a new pyrometer, he had found that platinum 

 immersed in mercury acquired a complete surface of that metal; 

 and now in keeping a strip of platinum foil in mercury for some 

 time, he found that its tenacity was unimpaired. A tube of 

 platinum, of about an inch in length, was accordingly welded to 

 the open end of a barometer-tube, with which the mercury form- 

 ing a perfect contact, would effectually prevent, it might be pre- 

 sumed, the insinuation of the air : the instrument was then 

 filled, and finished as usual. A mere ring of platinum also, 

 which wouldbe much less expensive, would be equally efficacious, 

 as the smallest surface of perfect contact must be sufficient. As 

 a considerable time, however, must elapse before the success of 

 this method could be shown by the barometer itself, the author 

 had instituted an experiment in which the effect would be sooner 

 apparent ;— he had confined a mixture of oxygen and hydrogen 

 over mercury in two jars, one of them having a ring of platinum. 

 at its lower extremity. He had not been able to disco- 

 ver in reuisters of barometrical observations any distinct evi- 

 dence of the gradual deterioration of barometers from the cause 

 he had thus endeavoured to obviate ; the observers, however, 

 having frequently found it necessary, for some reason, either to 

 re-boil the mercury in the tube, or 'to change their instrument 



altogether 



ASTRONOMIC A I. SOCIETY. 



This Society held its first meeting after the summer recess, on 

 Friday the 12th of November ; the President, H. T. Colebrooke, 

 Esq. in the chair. Several new members were elected, and 

 others proposed, and a great number of valuable presents, espe- 

 cially from foreign astronomers, were announced. 



Two communications were read from Sir Thomas Brisbane, 

 Governor of New South Wales. The first of these contained an 

 account of some observations made at Paramatta, by Sir Tho- 

 TSlew Series, vol. Ix. i. 



