INDEX. 385 



Velocity, not alone the actuating force of winds, but also the 



degree of density, i. 302. 

 Velvet-duck, a variety of the common duck, a native of the 



European dominions, iv. 420. 



Vermin, hospitals erected in India for the maintenance of all 

 kinds of vermin, ii. 84. Less found with asses than with 

 other animals covered with hair, 211. See Bramins. 

 Vesuvius, its eruption; the most remarkable described by 

 Valetta, i. 81. Another account by Bishop Berkeley, 83. 



Vibrations (of a bell), cease to be heard when under the re- 

 ceiver of an air-pump, i. 285. The tone of a sonorous body 

 made to depend upon the number of vibrations, not the 

 force, is a mistake of an effect for a cause, ii. 35. 



Violet-crab, of the Caribbee Islands, most noted for shape, 



delicacy of flesh, and singularity of manners, v. 168. 

 Viper, most vivacious of reptiles ; experiment on a viper in 

 the receiver of the air-pump by Mr Boyle, i. 270. Kept 

 in boxes for six or eight months without any food ; its pro- 

 gressive motion, v. 361. The only animal in Great Britain 

 whose bite is feared ; do not devour their young ; their 

 food ; by the application of salad-oil the bite of the viper 

 effectually cured ; who first discovered the remedy ; effects 

 of the viper's bite, v. 359. 



Vision, its errors; objects represented upside down, and 

 double, ii. 21. The point without sensation ; and want of 

 measure for distance, 23. 



Viviparous and oviparous animals, the two classes for genera- 

 tion and production ; all other modes held imaginary and 

 erroneous, i. 364. The blenny, a spinous fish, brings forth 

 two or three hundred young at a time, alive, and playing 

 around, v. 21. 



Unau, one of the two kinds of the sloth, an animal about the 

 size of a badger, iii. 406. 



Understanding, comparative progress of it : greater in infants 

 than in children three or four years old, i. 396. 



Undulations (in elastic bodies), supposed by the ear one con- 

 tinued sound, though in reality many, ii. 34. 



Unicorn (of the sea), a whale with teeth in the upper jaw, its 

 description, v. 47. See Narwhal. 



Univalve shells 1 , first division by Aristotle, as to figure, v. 208. 



Voice (of birds) much louder for their bulk than animals of 

 other kinds: some set to music by Father Kircher, iv. 118. 



Volcano, considered as a cannon of immense size, the mouth 

 near two miles in circumference : opinion of philosophers 

 and ignorant men about it : the real causes : three very re- 

 markable in Europe, and which, i. 77. Albouras, most 

 famous in Asia : one in the island of Ternate : in the Mo- 

 lucca Islands, in Japan, in Java, and Sumatra, in the Cape 



VOL. VI. B b 



