76 



Kow, Dr. Hutton obtained from this formula the value of (n) = 2*400 

 atmospheres, or 15-J tons per square inch. The result, as Mr, Longridge 

 observes, is far from accurate : as the variation of pressure must be 

 allowed for Mariotte's law, by adopting the true thermo-dynamical law, 

 we have 



(p + w) v 2 



— ; 



or, applying it to Mr. Whitworth's 80-pounder, with a velocity of 

 1300 feet per second, a pressure of 24-58 tons per square inch. 



Por the different equations for the velocity of the centre of oscilla- 

 tion, Dr. Hutton deduced the formula — 



biv __ 5-6727 c I pgo + bii 

 pg + hi r pg + hi ' 

 from which equation we get 

 5*6727 c 



bir 



V (pgo + bii) x (pg + hi), 



the true expression for the original velocity of the ball, before it strikes 

 the pendulum, by extracting the root of the compound factor, 



(pgo + bii) x (pg + hi), 



we have 



, . o + i 

 P9 + ~20~ X 



a formula within the jq o o °^ ^he ^ rue Y8 ^ ue > from which the value 

 can be estimated. 



v = 5-6727 gc. P ~ Vo~. 



The speed of most iron-clads, strange to say, is, notwithstanding the 

 immense weight of their superincumbent armour, superior to the ex- 

 pectations of their designers. The greatest speed yet obtained has been 

 that of the " Achilles ;" this vessel obtained a speed at full boiler power 

 of sixteen knots. The "Warrior" obtained a speed of 13 J knots at 

 a mean draught of 26-J feet, completing her circle in eight minutes and 

 thirty seconds, while the " Mersey" took forty minutes ; one of our crack 

 3000 ton frigates took no less than eleven minutes and fifteen seconds 

 to do the. same. The length of the "Mersey" is 287 feet 15 T 3 o inches, 

 and that of the " Warrior" 383 feet 2f inches, which makes the "War- 

 rior's" superiority the more remarkable, and proves that a long ship 

 can answer the wheel as well as a short one ; but in stability little can 

 be said for vessels of the " Warrior" class. The index pendulum on the 



