Steam-Engine Indicator. 93 



It has long. been a maxim with us, and we believe is pretty 

 generally acted upon by those at the head of manufacturing 

 estabhshments, to receive and adopt the reports of our work"- 

 men upon things of which we think they have, from their differ- 

 ent occupations, an opportunity of forming a just opinion : the 

 present instance shews, however, that even in a situation where 

 their daily expenditure of exertion was increased at least 15 or 

 20 percent., they were unconscious of the change, and would 

 only be convinced of its existence by a rapid transition from 

 one extreme to the other. The results, therefore, of experience, 

 orrathertheopinions which men form when, from the nature 

 of the subject, their observations are confined to effects alone, 

 ought to be received with care, and acted upon with caution ; 

 and it is only upon the unbiassed results exhibited to our actual 

 observation, through the medium of inanimate matter, acting on 

 known principles, that implicit confidence ought to be placed- 

 The indicator is an instrument of this kind; it exhibits to our 

 view the successive changes of pressure which take place in a 

 steam-engine cylinder during each stroke; and by also marking 

 the duration of each particular pressure, it affords, with an ele- 

 gant simplicity, a very near and correct approximation to the 

 power exerted. The results which it yields are so tangible, and 

 in many situations so important and instructive to those who 

 have the distribution and application of the power derived from 

 steam-engines, that we think it only requires to be more gene- 

 rally known and understood, to be oftener applied. 



H. H. Jur>. 



Glasgow, 4th Feb. 1822. 



Description of a Steam- Engine Indicator.— Plate II. 

 A— Steam-engine cylinder cover. 



B ,S/o;3-coc^— usually made to answer the seat of the grease- 

 cock. 



C Indicator cylinder-ahout U inches diameter, and 8 inches 

 long, open at top, and screwed at bottom upon the stop- 

 cock B. 



