ANNOTATIONS AND~ABDITIONS. 397 



but the neglected correction for the height of the mercury in the 

 cistern has somewhat disfigured the results as there published. 

 When it is remembered that the results given in the above table 

 were obtained with barometers of very different constructions, at 

 various hours of the day, with winds from very different quarters, 

 and on the unequally heated declivity of a volcano, in a locality in 

 which the decrease of atmospheric temperature differs greatly from 

 that which is supposed in our barometric formulae, the agreement 

 will be found to be as great as could be expected, and quite satis- 

 factory. 



My measurements in 1822, at the time of the Congress of Yerona, 

 when I accompanied the late King of Prussia to Naples, were made 

 with more care and under more favorable circumstances than those 

 of 1805. Differences of height are besides always to be preferred 

 to absolute heights, and these show that, since 1794, the difference 

 between the heights of the edges of the crater at the Rocca del Palo 

 and on the side towards Bosche Tre Case has continued almost the 

 same. I found it in 1805 exactly 69 toises (441 English feet), and 

 in' 1822 almost 82 toises (524 English feet): A distinguished 

 geologist, Mr. Poulett Scrope, found 74 toises (473 English feet), 

 although the absolute heights which he assigns to the two sides of 

 the crater appear to be rather too small. So little variation in a 

 period of twenty-eight years, in which there were such violent com- 

 motions in the interior of the crater, is certainly" a striking pheno- 

 menon. 



The height attained by cones of scorise rising from the floor of 

 the crater of Vesuvius is also deserving of particular attention. In 

 1776, Schuckburgh found such a cone 615 toises, or 3932 English 

 feet, above the surface of the Mediterranean i according to the mea- 

 surements of Lord Minto (a very accurate observer), the cone of 

 scoriae which fell in on the 22d of October, 1822, even attained the 

 height of 650 toises, or 4156 English feet. On both occasions, 

 therefore, the height of the cones of scoriae in the crater surpassed 

 that of the highest part of the margin of the crater. When we 

 compare together the measurements of the Rocca del Palo from 

 1773 to 1822, we are almost involuntarily led to entertain the bold 

 conjecture that the north margin of the crater has been gradually 

 34 



