412 REPORT — 1872. 



To the Mechanical Engineer it is a great boon, as by its use he is enabled 

 rapidly and with accuracy to find the average pressure upon the piston of a 

 steam-engine as given by indicator diagram : all that is necessary is to 

 ascertain the area of the figure, then to divide that area by the length and 

 the mean height; the representative of the average pressure is at once 

 obtained. 



There are, no doubt, other instances in which such an implement is of great 

 use, but the writer feels it is unnecessary to adduce them in support of the 

 claim of the planimeter to the consideration of engineers and of meu of 

 cognate professions ; and he brings his paper to a conclusion with the expres- 

 sion of a hope that he has by the use of plain, in fact homely, description 

 solved the problem which he set himself in the outset, and has made it clear 

 how it is that the area of any figure, however irregular, can be recorded in 

 definite standard units of measurement by the mere passage of a tracer along 

 the perimeter of that figure. 



