OF ARTS AND SCIENCES. 381 



Professor Agassiz made a communication upon the copula- 

 tion of the Selachian Fishes. 



Prof. Treadwell read an elaborate paper on the force of i&red 

 gunpowder, the strength of guns, and the velocity of projec- 

 tiles ; being a continuation of the examination made by him, 

 at the January meeting, of Captain Rodman's instruments and 

 experiments. 



The examination of the subject this evening was made in special 

 reference to the partial and conditional defence made by Professor 

 Peirce, at the February meeting, of the accuracy of the instruments 

 and experiments of Captain Rodman. Professor Treadwell explained 

 the action of gunpowder, by referring it to the measure of the force of 

 a column of liquid by which a jet is projected through an aperture in 

 the side of a vessel. He then exhibited diagrams showing the force of 

 powder in a cannon, during its development and action upon the ball ; 

 and, taking a particular case given in Captain Rodman's book, page 

 197, he showed that the measures of the force, as there given, were 

 impossible, both in character and amount, as the ordinates representing 

 the forces through the caliber are actually greater near the muzzle 

 than nearer the breech. He then deduced, from the mean of all the 

 ordinates, that the force produced by 12,67 pounds of powder must, if 

 true, in this case have given a velocity of 2,966 feet a second to a ball 

 of 186.3 pounds weight ; when it is shown by the experiments of Cap- 

 tain Mordecai that a charge of 12 pounds will produce only a velocity 

 of 2,046 feet a second in a 24-pound shot. He showed, moreover, that 

 in this very experiment of Captain Rodman, where, if the instrumen- 

 tal measures of the force had been correct, the resulting velocity must 

 have been 2,966 feet, the velocity actually produced was, as measured 

 by Captain Rodman himself, only 920 feet a second. He then pro- 

 ceeded to demonstrate from all the preceding examination, that the 

 actual mean pressure of the powder was but 3,390 pounds per square 

 inch; whereas it is indicated by Captain Rodman's instrument at 

 35,213 pounds per inch ; and hence that the instrumental measure is 

 10.38 times greater than the true measure. 



