490 MEMOIR OF DANIEL TREADWELL. 



to the Departments, and I was struck in some instances with the extravagant and nnscrnpnlons 

 eagerness of common persons who tliought they had discovered a way of getting rich. 



1 hope the decision of the court in your prosecutions of the Parrotts will award you — what 

 you value more than money — the honor and merit of being the first to conceive of, and to 

 employ, coiled spiral rings in the construction of wrought iron guns. 



Pray remember me most cordially to Mrs. TreadwcU, and believe me your constant and 



faithful friend. 



C. n. Davis. 



Professor Winlock of the Harvard College Observatory, at a meeting of the Ameri- 

 can Academy, September, 1866, read a paper by Professor Treadwell " On the Com- 

 parative Strength of Cannon of Modern Construction." 



The standard gun is assumed to be the old 32-pounder, with a charge of eight 

 pounds of powder and one shot, with an initial velocity of 1,000 feet a second ; the 

 standard unit of force is taken as the height to which the shot would rise in vacuo, or 

 40,000 feet; this multiplied by the weight of the shot, 32 pounds, gives 1,280,000 

 pounds raised one foot in one second as the measure of force. 



To determine the strength of the gun, as well as the force of the shot: "Having 

 already seen that our standard 32-pound shot has a force of 1,280,000 pounds raised 

 one foot, if we divide this product representing the strength of the whole gun by 

 the weight of the metal of which the gun is made up in pounds, we shall obtain the 

 strength or work which may be done by one pound of the metal of which the gun is 

 constituted. We shall find the result of this computation (the weight of our standard 

 32-pounder being 7,500 pounds) to be C-WoV- = ^'^^) ^^^ pounds in shot raised 

 one foot by every pound of metal which forms the body of our standard gun." 



This computation, applied to the Dahlgren, Eodman, and Armstrong guns, gives 

 the following residts. The number of pounds of shot raised one foot by each pound 

 weight of the gun is, for the Dahlgren, 144.7 pounds; the Rodman, 125; the Arm- 

 strong, 372.8.* 



To Dr. William Sweetser. 



Cambridge, November 4, 18G8. 

 My dear old Friend, — I received your most kind letter early in September, but my infirm 

 state and some special annoyances have prevented me from answering it until this late day. A 

 letter from you is always most welcome to me. It is especially so now, when oppressed with 

 pain and many infirmities. I am heartily glad to know that your health has continued sound 

 notwithstanding your seventy years, and that you make light of the Davidian period ; that you 

 can walk at pleasure, and, as I trust, have tlie advantage of a good appetite for food, and the enjoy- 

 ment and vigor that flow from indulging it. I congratulate you also on tlie philosophical quiet 



* For correction of error as to Armstrong gun, — 261 instead of 372.8, — see Proceedings of the American 

 Academy, September 11, 1806, Vol. VII. p. 412. 



