world. His ingenuity is unquestionable; but it is thrown 

 away on inventions ^vhich betray, in a very remarkable 

 manner, the absence of true philosophical conceptions of 

 the physical ideas embodied in their operations; and their 

 fallacies are so curiously concealed in his contrivances, that 

 he is not only led astray himself, but many people are 

 induced to follow him in pursuit of the ignis fatuus of his 

 vagrant imagination. 



Any careful student of Captain Ericsson's engineer- 

 ing activities — as distinguished from his promotional 

 activities — must sympathize with Mr. Cheverton, 

 even though he may not fully subscribe to his senti- 

 ment. Certain it is, however, that the epic of the 

 Ericsson demonstrated dramatically, as no lesser under- 

 taking could have done, the uncertain state of under- 

 standing of the principles of engineering thermo- 

 dynamics in the 1850's. 



Estimate of Power Developed 



The following calculations, based on approximate 

 data, have been made to support my estimate of 250 

 horsepower output of the Ericsson's engine (page 50). 

 The net work output at the paddle shaft is determined 

 as the difference between the working cylinders' 

 output and the input to the supply cylinders, re- 

 duced by factors to account for departure of the 

 actual from idealized operating conditions. 



The maximum design pressure of the engine was 

 12 pounds per square inch gage. The reports of 

 the trial trip agree on 8 pounds per square inch as 

 the attained pressure. I have found no evidence 

 that a higher pressure was attained while this engine 

 was in the ship. 



The data upon which my calculations were based 

 are as follows: 



Working cylinders, single acting 



Number of cylinders 4 



Diameter of each cylinder 1 4 ft. 



Length of stroke 6 ft. 

 Supply (compressor) cylinders, single acting 



Number of cylinders 4 



Diameter of each cylinder " ft. 5 in. 



Length of stroke 6 ft. 



Clearances (assumed) o 



Inlet air pressure (assumed) i4.5p.s.i. 



abs. 



Maximum air pressure in cycle, approx. 8.3 23.0 p.s.i. 



p.s.i. gage abs. 



Point of cutoff in working cylinder % stroke 



Working strokes per minute 9 



The work output of a single working cylinder 

 during one cycle of operation (one revolution) is 

 represented in figure a by the area bounded by the 

 p-v trace 1-2-3-4-5. Cylinder volumes at point of 

 cutofT, V3, and at end of stroke, 04, are 680 and 906 

 cubic feet, respectively. Assuming isentropic ex- 

 pansion of air during process 3-4, p4 can be shown to 

 be 15.4 pounds per square inch absolute. 



Work, W, for the individual processes is calculated 

 as follows: 



Wi_2=0 (1) 



W.2^s=P2{v3-v2) = 23.0XU4{6S0-0) 



= 2,250,000 ft. lb. (2) 





2 













3 



Poi n t 

 c u t f 



of 



f 





23 



J. 21 

 



.-■ " 



d. 

 , 17 



V 



•^ 15 



ft) 



a. 



9 









8 





















\ 

















A 







/ 1 









a 









\' 



v' ; C 



n s f. 







b 





V 



p v° : 



const. 



19 

















\ 















\ 



V 























K 



4 

 1 













\ 





16 



1 

















1 e 















k -, 









6 















loo 200 300 400 500 600 700 800 900 

 Cylinder volume , cu. ft. 



loo 200 30 



Cylinder v 



o 400 500 600 700 

 olume , cu. ft. 



Figure ii. — Pressure-volume diagram: a, For working cylinder; b, for supply cylinder. 



PAPER 20: JOHN ERICSSON AND THE AGE OF CALORIC 



59 



