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 phænomenon.
The height attained by cones of scoriæ 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: according to the measurements of Lord Minto, (a very accurate observer,) the cone of scoriæ 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 scoriæ 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 upraised by subterranean forces. The accordance of the three measurements between 1773
