94 VISCOUS THEORY OF GLACIER MOTION. [1845. 



Catania, described the first thirteen miles of its course in twenty 

 days, or at the rate of 162 feet per hour, but required twenty- 

 three days for the last two miles, giving a velocity of twenty-two 

 feet per hour ;* and we learn from Dolomieu, that this same 

 stream moved, during part of its course, at the rate of 1500 

 feet an hour, and in others took several days to cover a few 

 yards.f 



The lava of 1753 (Vesuvius), starting with a velocity of 

 2500 feet per hour, soon -diminished to sixty feet,J as did that 

 of 1754 to the same; and of 1766 to thirty feet per hour.|| 

 The lava of 1831 (Vesuvius) moved over 3600 feet in twenty- 

 six hours, and finally advanced steadily at the rate of ten feet 

 an hour. If The lava of Etna of November 1843, is said to 

 have moved over three paces per second at the distance of a 

 mile from the crater. 



The stream of 1761 (Vesuvius), before it stopped flowing, 

 advanced but three yards a-day ;** and that of 1766, which con- 

 tinued moving for about nine months, moved over but a small 

 space in that time. Had the attention of authors been equally 

 directed to the slow as to the rapid advancement of lava, there 

 is no doubt that we should find many instances besides these 

 recorded by Dolomieu and Scrope, of continuous movements of 

 three feet, and even one foot a-day, or less. 



* Ferrara, Descr. del Etna, p. 105. This appears from the dates, though at 

 variance with one assertion of the author. 



f Dolomieu, Isles Ponces, p. 286, Note. \ Delia Torre, Histoire, etc., p. 196. 



Ihid, p. 130. j| Hamilton, Campi Phlegrsei, i. 19. 



^f Auldjo, Sketches of Vesuvius, p. 79, with a sketch of the front of the stream 

 whilst advancing at this rate. 



** Delia Torre, p. 182. 



