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An Account of the Effect of Mercurial Vapours on the Crew of His 

 Majesty's Ship Triumph, in the Year 1810. By William Burnett, 

 M.D. one of the Medical Commissioners of the Navy, formerly Phy- 

 sician and Inspector of Hospitals to the Mediterranean Fleet. Com- 

 municated by Matthew Baillie, M.D. F.R.S. Read June 19, 1823. 

 [Phil. Trans. 1823,/>. 402.] 



The Triumph arrived at Cadiz in 1810, and in the following March 

 a Spanish vessel, laden with quicksilver, was wrecked under the bat- 

 teries, then in possession of the French. The Triumph's boats were 

 sent to her assistance, and about 130 tons of the quicksilver carried 

 on board. The metal was secured in bladders packed in barrels, but 

 the bladders having been wetted grew rotten, and the metal escaped 

 in large quantities, got mixed with the provisions, and very soon af- 

 fected the crew with ptyalism, ulcerated throats, &c. The different 

 animals on board were also affected. From the extent of the mis- 

 chief it was evident that the air of the confined part of the vessel 

 contained mercurial vapour, and accordingly those who slept and 

 messed in the orlop and Tower decks were more severely affected 

 than those chiefly confined to the upper deck ; while the men who 

 lived and slept chiefly under the forecastle, escaped with a slight af- 

 fection of the gums. 



On the Astronomical Refractions. By J. Ivory, A.M. F.R.S. Read 

 June 19, 1823. [Phil. Trans. 1823,;?. 409.] 



The ancients, Mr. Ivory observes, were acquainted with the ex- 

 istence of atmospherical refraction ; but the first that ascertained its 

 magnitude with tolerable accuracy, and employed it in his calcula- 

 tions, was Tycho Brahe". Cassini attempted to compute the refraction 

 upon optical principles, and upon the hypothesis of an uniform me- 

 dium of uniform density, a supposition which, though very simple, 

 is sufficiently correct to a considerable extent. The next step was 

 to imagine an atmosphere of a density uniformly decreasing as the 

 height increases. Kramp was still more accurate in attending to the 

 true effects of pressure and change of temperature ; his methods have 

 been improved and extended with great sagacity by Laplace, and the 

 tables founded on his computations are perhaps the best in existence 

 with respect to the value of the mean refractions. 



An uniform atmosphere must be supposed to be five miles in height; 

 an atmosphere uniformly decreasing in density ten. Kramp and 

 Laplace consider it as infinite. The former limits would make the 

 horizontal refraction less than the truth ; the latter supposition much 

 greater. Mr. Ivory is inclined to suppose some considerably ex- 

 tended, though finite height, which shall give the true refraction at 

 the horizon, and which will probably be also correct for all other 

 cases ; and he thinks it not superfluous to inquire, whether such an 

 atmosphere would afford results sensibly different from those of an 

 atmosphere of infinite extent. The phenomena of twilight and of 



