Translations and abstracts from the French. 265 



a certain continued electric tension, which invincibly opposes 

 the combination of oxygen with the metal, though that ac- 

 tion is so strongly manifested on ordinary occasions. 



I assured myself that a certain duration of contact of the 

 metal is necessary to effect this state of things, for when I 

 interrupted the contact in a similar apparatus, which had 

 been in operation but a few days, the copper was speedily 

 oxidated. 1 am engaged in new researches to ascertain the 

 limit of lime necessary to effect this preserving power, and 

 also the limits of the preservation itself* 



The copper of the apparatus whose contact was inter- 

 rupted after forty seven days, stili continues, (now more than 

 twenty days,) perfectly preserved, and no indications of oxi- 

 dation appear m the vessel. 



5. Maximum density of water. — A series of experiments 

 to determine the question of the probability of there being 

 a superior current in the ocean, setting from the equator to- 

 wards the poles, and an inferior current from the poles to 

 the equator, has been made by G. A. Ermann, Jr. 



This question, the author observes, depends necessarily 

 and exclusively on the solution of another, that is whether th© 

 water of the sea, Hke fresh water, attains its maximum of 

 density before it arrives at the point of congelation. 



Four methods of trial were pursued. 



1. By taking the specific gravity of the water at different 

 temperatures by an excellent hydrostatic balance. 



2. By Nicholson's areometer. 



3. By the method of Dr. Hope, in determining the tem- 

 perature of ascending and descending currents. 



4. By a simple and elegant method suggested by the 

 other, viz. the determination of the intervals of time in the 

 cooling of the water under examination, through every suc- 

 cessive half degree, from 15° or 20" F. above, to the freez- 

 ing point. 



* My experiments have led me to perceive that Sir H. Davy, in the Bake- 

 rian Lecture oi 1826, has committed a serious error in recommending the use 

 of zinc or tin in the preservation of steam boilers in which sea water is used. 

 I have tound decisively, that tin, far from preserving iron, is on the contrary 

 preserved by it. Hence a piece of tin introduced into a a boiler, instead of 

 diminishing the danger of explosion by preserving the boiler, would power- 

 fully contribute to its destruction. 



Vol. XVI.— No. 2. > 7 



