207 



side (or within the interior surface of the stratum) with equal force 

 in opposite directions. 



On the Corrosion of Copper-sheeting by Sea-water, and on Methods of 

 preventing this Effect ; and on their Application to Ships of War 

 and other Ships. By Sir Humphry Davy, Bart. P.R.S. Read 

 January 22, 1824. [PAzY. Trans. 1824, p. 151.] 



When copper sheeting, however pure the metal may be, is exposed 

 to sea- water, a green rust is formed upon it ; which, when washed 

 off, is replaced by a similar substance, till the whole of the metal is 

 thus destroyed by corrosion. To prevent this effect, the President 

 avails himself of the modification of chemical affinities, derived from 

 electrical power ; and in pursuing his researches in relation to this 

 subject, he found the above-mentioned action upon copper counter- 

 acted by any weak negative electricity easily excited in it by the 

 contact of a surface of tin not exceeding -rro-th that of the copper, 

 and made part of an electric circuit in sea- water. Other metals may 

 be substituted, but the facility with which a perfect contact is made 

 by solder with tin, and the facility with which its submuriate de- 

 taches from the metal, induce Sir Humphry Davy to regard it as 

 best adapted to the purpose. He observes, further, that the cause 

 which prevents the oxidation of the copper will also probably pre- 

 vent the adhesion of marine animals and of vegetables. After ad- 

 verting to the unequivocal and satisfactory results of his experiment 

 made upon a small scale, the author states that the Lords Commis- 

 sioners of the Admiralty have enabled him to make arrangements 

 for pursuing them upon a very extended plan. 



A finite and exact Expression for the Refraction of an Atmosphere 

 nearly resembling that of the Earth. By Thomas Young, M.D. 

 For.Scc.R.S. Read February 5, 1824. {Phil. Trans. 1824,;?. 159.] 



Having shown that if the pressure of the atmosphere be represented 

 either by the square, or by the cube of the square root of the density, 

 the astronomical refraction may be attained in a finite equation; and 

 having adverted to Mr. Ivory's computation of the refraction with 

 the assistance of converging series, and several transformations from 

 an equation which expresses the pressure in terms of the density and 

 of its square, Dr. Young proceeds to observe, that if we substitute 

 for the simple density the cube of its square root, we shall represent 

 the constitution of the most important part of the atmosphere with 

 equal accuracy, although this expression supposes the total height 

 somewhat smaller than the truth ; and that we shall thus obtain a 

 direct equation for the refraction, which agrees very nearly with Mr. 

 Ivory's table, and still more accurately with that in the Nautical Al- 

 manac, and with the French tables. 



At the horizon the refraction is equal to 33' 49"'5, which is only 

 1"*5 less than the quantity assigned by the French tables and in the 



