OF ARTS AND SCIENCES : FEBRUARY 9, 1864. 239 



" The Committee have examined all the air-engines in Boston that 

 they have been able to find after diligent inquiry, and they believe that 

 they have obtained as much and as accurate information in regard to 

 them as could be had ; and as much as seemed, in the pi-esent state 

 of the question, useful. 



"They find three kinds of engines in practical operation: 1st, Mr. 

 Ericsson's, to which the Rumford medal was awarded by the Academy 

 at the adjourned annual meeting in June, 1862 ; 2d, Mr. Shaw's ; 

 and 3d, Mr. Roper's. Engines by these inventors were at work in 

 Boston or its vicinity at the time of that award, and were described in 

 the discussions which were had on the Report of the Rumford Com- 

 mittee at that time. The Ericsson engines which were then at work 

 in Boston are still at work ; but the Committee have not been able to 

 find that another of this kind has been added to the number ; and they 

 believe that no addition has been made. 



" All measurements of these engines have shown that their nominal 

 power greatly exceeds their actual useful effect. The Committee have 

 found, in every one measured, the actual power to be only from one 

 eighth to one seventh of that for which the engine was purchased. 



" The first one submitted to the Rumford Committee of the preced- 

 ing year (estimated at one horse-power) measured only one seventh of 

 one horse-power. Two other four-horse engines each measured from 

 two thirds to three fourths of one horse-power; and the two-horse 

 engine at the office of the 'Medical Journal' measured only one fourth 

 of one horse-power. These engines consume about fourteen pounds of 

 coal to the horse-power per hour. These measures were taken as the 

 machines were found at their ordinary work, and are believed to ex- 

 press with sufficient accuracy their performance under ordinary cir- 

 cumstances. 



" The engines of INIr. Shaw and Mr. Roper, while they differ from 

 each other in some important particulars, are similar in the points to 

 which the former Rumford Committee attached most value. They 

 both work under pressure, and heat the air by passing it directly 

 through the flame, without the intervention of any conducting sub- 

 stance. They are also independent of the draught of a chimney, and 

 are as effective in the attic as in the basement of a building ; more- 

 over, they are almost, if not quite, as steady and as noiseless as a 

 steam-engine. 



" Mr. Shaw, during the past year, has been engaged in experiment- 



