88 Mr. Daniell on the Barometer. 



tenacity. I availed myself of this property in the following 

 way : — I caused a small thin piece of platinum tube to be made 

 about the third of -an inch in length, and of the diameter of the 

 glass tube ; this was carefully welded to its open end, so that the 

 barometer tube terminated in a ring of platinum. The tube was 

 filled and boiled as usual, and the infiltration of air was com- 

 pletely prevented by the adhesion of the mercury, both to the 

 interior and exterior surface of the platinum guard. I have no 

 doubt that a mere ring of wire welded, or even cemented upon 

 the exterior surface of the glass, which would be a much easier 

 and less expensive operation, would be a sufficient protec- 

 tion, as the slightest line of perfect contact must effectually ar- 

 rest the passage of the air : but in the first attempt I was de- 

 sirous that the experiment should be tried in the most perfect 

 manner. When a piece of glass, armed either with a ring or 

 tube, is immersed in mercury, the effect is easily perceived ; in- 

 stead of any depression being visible around it, the mercury may 

 be lifted by it considerably above its proper level. Time, of 

 course, will be requisite fully to confirm the efficacy of the 

 guard, and I was in hopes that the Royal Society would have 

 attributed weight enough to the observations which I submitted 

 to them, to induce them to give orders for the construction of a 

 large barometer, upon the principle which I have suggested, to 

 be placed beside the two others already in their possession. An 

 opportunity would thus have been afforded of determining, in the 

 most unexceptionable manner, several facts of the utmost im- 

 portance to meteorological science. The further experiments 

 which the council have called for, before they would commit 

 themselves by the publication of the foregoing opinions, are in 

 progress, and shall be laid before the Society as soon as they 

 are complete ; but they obviously require considerable time for 

 their progress. I have taken the pains to re-write this paper, 

 under the conviction that advantage will be derived to science, 

 by sooner throwing the subject open to general observation and 

 experiment. 



I expected to have been able to find some evidence of the de- 

 terioration of barometers in the numerous registers that are kept 



