422 



the chlorine is found to divide itself equally between the other 

 two. 



So also with respect to the relative affinities of carbonic oxide for 

 chlorine or for oxygen. The new gas is not decomposed by oxygen, 

 neither is carbonic oxide altered by admixture with any proportion 

 of chlorine that has been tried. 



A Narrative of the Eruption of a Volcano in the Sea off the Island of 

 St. Michael. By S. Tillard, Esq. Captain in the Royal Navy. Com- 

 municated by the Right Hon. Sir Joseph Banks, Bart. K.B. P.R.S. 

 Read February 6, 1812. [Phil. Trans. 1812,^. 152.] 



The eruption here described by Capt. Tillard was first observed by 

 him on the 12th of June, 1811, having burst forth only two days 

 before. It had been preceded by another eruption in the month of 

 January, about three miles distant. Having come to anchor on the 

 13th in the road of Porta del Garda, Capt. Tillard set off on the fol- 

 lowing morning with some other gentlemen, for the purpose of wit- 

 nessing the phenomena from the adjacent cliffs of St. Michael. The 

 place of the eruption was scarcely a mile from the base of the cliff, 

 which was nearly perpendicular, and about 400 feet high. 



In the most quiescent state of the volcano, there appeared a cir- 

 cular body of smoke over the surface of the water, in continual rota- 

 tory motion, extending itself to leeward ; but suddenly a column of 

 very black ashes and cinders would shoot up, in the form of a spire, 

 inclined from ten to twenty degrees from the perpendicular ; and, 

 again, & second, third, and fourth column, each overtopping the pre- 

 ceding, till the last appeared more above the level of the eye than 

 the sea was below it. 



When the first impetus that raised the column ceased, the smoke 

 was seen to break into various fanciful forms ; some ascending by their 

 proper levity, others carried downwards by the particles of falling ashes, 

 so as to give the appearance of pendent plumes of black and white. 



These bursts were always accompanied by vivid flashes of light- 

 ning in the densest part, and followed by a succession of water- 

 spouts that appeared drawn up by the masses of smoke as they rolled 

 away before the wind. 



The part of the sea where the volcano was situated was known 

 to be full thirty fathoms deep ; but in the course of the time that 

 Capt. Tillard and his friends were watching it, a ridge was seen to 

 project above the surface of the water ; and before they quitted the 

 cliff, which was in about three hours, a complete crater was formed, 

 apparently 400 or 500 feet in width, and elevated on the leeward 

 side not less than twenty feet in height. 



The great eruptions were generally attended with sounds like the 

 firing of cannon or musquetry, and often with slight shocks of earth- 

 quake. 



On the next day the volcano continued to emit clouds of black 

 smoke and ashes, but was comparatively tranquil. 



