A 



JOURNAL, 



OF 



NATURAL PHILOSOPHY, CHEMISTRY, 



AND 



THE ARTS. 



DECEMBER, 1806. 



ARTICLE I. 



. Facts and Observations respecting Vision under Water ; 

 and various Particulars relative to Swimming, Sfc» . 

 In a Letter from James Horsburgh, Esq. 



To Mr. NICHOLSON. 



Sir, Walworth, Nov. 6, 1806. 



JL HE perusal of your observations relative to Swini- On swimming, 

 ming, in No. 58 of your Journal, and the letters from ^^^^ vision un- 

 your correspondent inserted in Nos. 60 and 61, affirming ^^ ^^ ^^* 

 that objects are visible to the human eye under water, 

 which concurs not with your opinion, encourage me to 

 state some few facts relative to this subject, the result of 

 my own observations. 



In high latitudes the sea is seldom transparent ; but Great transpa- 



within the tropics, and near the equator, the bottom U ^^^^J ^^ ^^^ 

 . . , . \. r^p t, sea between 



often visible m from ten to fifteen or twenty fathoms wa- tropics. Bet- 

 ter, when it consists of variegated coral or white sand and ^°"^ ^^^^ ^' ^^^ 

 coral mixed. In various parts of the Indian seas, ^^ ^^x * 

 Voi. XV,— Dec. 1806. Nn the 



