Supply 

 cy/inc/e 



32 - foot c/f'amefe 

 patjdte wheel 



Figure 5. — Conjectural reconstruction of arrangement of driving gear in the 

 Ericsson. Reporters at tlie trial run rode on the pistons. 



A remark of Thomas Ewbank, sometime U.S. 

 Patent Commissioner, became more and more per- 

 tinent as the acrimonious debate over the success or 

 failure of the caloric engine continued. "Why 

 theorize, argue and quarrel for months about the 

 weightof a piece of metal," said Mr. Ewbank, "when 

 the scales are at your elbows?" '* A Prony friction 

 brake dynamometer, although difficult to apply to 

 the ship's engine, could have been used on the so- 

 called 60-horsepower test engine that Captain Erics- 

 son built before proceeding with the Ericsson's engine. '= 



The scales are no longer at our elbows, and I have 

 found no complete nor entirely consistent set of data; 

 but I have made a calculation based upon data that 

 were published at the time,'^ making such assumptions 

 as now appear reasonable and in every case weighting 

 my assumptions in favor of the engine. The result, 

 at nine revolutions per minute of the paddleshaft, is 



^^ Journal of the Franklin Institute, 1854, vol. 38, p. 33. 



55 A Prony brake, used to test a rotary steam engine, is 

 described and illustrated in Appletons' Mechanics'" Magazine and 

 Engineers' Journal, 1852, vol. 2, pp. 26, 91. Such a brake was 

 shown at the Mechanics' Fair in Boston and was reported in 

 North American Review, January 1840, vol. 50, p. 227. 



36 The most complete listing is in Appletons' Mechanics' Maga- 

 zine and Engineers' Journal, 1853, vol. 3, pp. 39-40. 



about 250 horsepower. My calculation is shown on 

 pages 59 and 60. 



A comparison, of sorts, can be made with the reason- 

 ably corroborated performance figures for marine 

 steam engines. 



The resistance of the Ericsson, in the speed range 

 considered, probably varied more nearly as the cube 

 of the velocity, as Prof. William Norton of Yale 

 University asstimed in his calculations,^" than as the 

 square of the velocity, as Ericsson believed. There- 

 fore, an increase of speed from Oji to 1 3 knots would 

 require on the order of eight times the power output 

 at Gji knots; that is, nearly 2,000 horsepov/er. The 

 Arctic, a larger vessel, developed 2,290 horsepower;'* 

 the Washington, about the same size as the Ericsson, 

 developed 2,000 horsepower.'^ 



Professor Norton, basing his calctilations upon horse- 

 power figures for several ocean-going steamers at 

 various speeds, and taking into account the cross- 

 sectional area of the vessels' hulls, estimated the 

 horsepower that would be required to propel a vessel 



^T American Journal of Science and Arts, 1853, ser. 2, vol. 15, 

 pp. 393-413. 

 38 Scientific American, 1853, vol. 8, p. 189. 

 ^^ Scientific American, 1846-1847, vol. 2, p. 85. 



50 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



