Mechanical Science. 169 



tint, and render it brown or black. Paintings of the first mas- 

 ters are frequently injured in consequence of this effect, being 

 blotted, as it were, with spots of colour, which spoil the ef- 

 fect. An artist at Paris, who possessed a design of Raphael's 

 thus disfigured, and who was too careful of the original work 

 to re-paint the places, applied to M. Thenard for chemical as- 

 sistance. That chemist during his attempts, remembering the 

 effect of oxygenated water in converting the black sulphuret of 

 lead into a white sulphate, sent some water, very slightly oxy- 

 genated, to the artist, who, by applying it with a pencil, in- 

 stantly removed the spots, and restored the white. The fluid 

 was so weak as to contain not more than five or six times its vo- 

 lume of oxygen, and had no taste. Paper coloured by a slight 

 tint of bistre was not at all altered by it.— -Annales de €himiej 

 xiv. p. 221. 



5. Distant Visibility of Mountains. 



Distance in 

 Authorities. Miles. 



Himalaya mountains Sir W. Jones 244 



Mount Ararat, from Derbhend Bruce 240 



Mowna Roa, Sandwich Isles (53 leagues) 180 



Chimborazo (47 leagues) 160 



Peak of Teneriffe from South Cape 



ofLanzerota ,, 135 



Peak of Teneriffe from ship's deck .... 115 



Peak of the Azores Don M. Cagigal 126 



Temaheud ^Morier 100 



Mount Athos Dr. Clarke 100 



Adam's Peak 95 



Ghaut at the back of Tellichery . . . , .94 



Golden Mount from ship's deck .... 93 



Pulo Pera fromthetopofPenang .. 75 



The Ghaut at Cape Comorin 73 



Pulo Penang from ship's deck 53 



The last six observations, and that of the Peak of Teneriffe, 

 were made by a writer in the Calcutta Monthly Journal, The 

 first of the Peak of Teneriffe is from Humboldt's Personal Nar^ 



