174 Things not generally Known. 



used to tell the distance in sailing. Columbus, Juan de la 

 Cosa, Sebastian Cabot, and Vasco de Grama, were not acquainted 

 with the Log and its mode of application ; and they estimated 

 the ship's speed merely by the eye, while they found the dis- 

 tance they had made by the running-down of the sand in the 

 ampotellas, or hour-glasses. The Log for the measurement of 

 the distance traversed is stated by writers on navigation not to 

 have been invented until the end of the sixteenth or the begin- 

 ning of the seventeenth century (see Encyclopaedia BritanniGoL 

 7th edition, 1842). The precise date is not known ; but it is 

 certain that Pigafetta, the companion of Magellan, speaks, in 

 1521, of the Log as a well-known means of finding the course 

 passed over. Navarete places the use of the log-line in English 

 ships in 1577. 



LIFE OF THE SEA-DEEPS. 



The ocean teems with life, we know. Of the four elements 

 of the old philosophers, fire, earth, air, and water, perhaps 

 the sea most of all abounds with living creatures. The space 

 occupied on the surface of our planet by the different families 

 of animals and their remains is inversely as the size of the indi- 

 vidual ; the smaller the animal, generally speaking, the greater 

 the space occupied by his remains. Take the elephant and his 

 remains, and a microscopic animal and his, and compare them ; 

 the contrast as to space occupied is as striking as that of the 

 coral reef or island with the dimensions of the whale. The 

 graveyard that would hold the corallines, is larger than the 

 graveyard that would hold the elephants. 



DEPTHS OF OCEAN AND AIR UNKNOWN. 



At some few places under the tropics, no bottom has been 

 found with soundings of 26,000 feet, or more than four miles ; 

 whilst in the air, if, according to Wollaston, we may assume 

 that it has a limit from which waves of sound may be rever- 

 berated, the phenomenon of twilight would incline us to assume 

 a height at least nine times as great. The aerial ocean rests 

 partly on the solid earth, whose mountain -chains and elevated 

 plateaus rise like green wooded shoals, and partly on the sea, 

 whose surface forms a moving base, on which rest the lower, 

 denser, and more saturated strata of air. Humboldt's Cosmos, 

 vol. i. 



The old Alexandrian mathematicians, on the testimony of 

 Plutarch, believed the depth of the sea to depend on the height 

 of the mountains. Mr. W. Darling has propounded to the 

 British Association the theory, that as the sea covers three 

 times the area of the land, so it is reasonable to suppose that 

 the depth of the ocean, and that for a large portion, is three 



