246 STRUCTURE AND ACTION OF VOLCANOS. 



Naples, were made with more care and under more favourable 

 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 Bosco 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 commotions in the interior of the 

 crater, is certainly a striking phenomenon. 



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 Medi- 

 terranean : according to the measurement of Lord Minto, (a 

 very accurate observer,) the cone of scoriae which fell in on 

 the 22d of October, 1 822, 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 Kocca 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 upraised by subterranean forces. 

 The accordance of the three measurements between 1778 



