208 



iZanoni, Borda, and La Condamine. The reader 

 versed in the practice of levelling will not be 

 astonished at the very gentle slope, which these 

 profiles seem to indicate. In nature, an in- 

 clined plane of an angle of .35° appears to be 

 50° : we scarcely dare go down a hill of 22° slope 

 in a carriage ; and the parts of the volcanic cones, 

 that are inclined 40° or 42°, are almost inacces- 

 sible, though the foot may form steps by plung- 

 ing it in the ashes. I have recorded in a note* 



* In places where there were at the same time slopes 

 covered with tufted grass and loose sands I took the following 

 measures : 



5°, slope already of a very marked inclination. In France the 



high roads must not exceed 4° 46' by law ; 

 15°, slope extremely steep, and which we cannot descend in a 



carriage 5 



37°, slope almost inaccessible on foot, if the bottom be a nak- 

 ed rock, or a turf too thick to form steps. The body falls 

 backwards when the tibia makes a smaller angle than 53°, 

 with the sole of the foot ; 



42°, the steepest slope that can be climbed on foot in a ground 

 that is sandy, or covered with volcanic ashes. 



When the slope is 44°, it is almost impossible to scale it, 

 though the ground] permits the forming of steps by thrusting 

 in the foot. The cones of volcanoes have a medium slope 

 from 33° to 40°. The steepest parts of these cones, either of 

 Vesuvius, the Peak of TenerifFe, the volcano of Pichincha, 

 or Jorullo, are from 40° to 42°. A slope of 55° is quite 

 inaccessible. If seen from above it would be estimated at 

 75°. 



