310 SCALE FOR THE COMPUTATION OF AREAS^ ETC. 



upon which the Grovernment maps are drawn, would facilitate 

 the operation of computation, and be much less liable to inaccuracy. 

 I drew the scales upon tissue paper, and laying them over the island 

 or broken frontage, of which the contents were required, I had only 

 to count the acres corered by the squares, adding parts of acres 

 where the lines intersected the squares. 



Long use of this instrument has proved not only to myself but to 

 others in the office, that the eye in judging of the parts of acres, in 

 this method, is more to be relied upon than in the usual manner of 

 computation by square and compass. 



I am induced to lay this communication before the Canadian In- 

 stitute for the purpose of its being more generally known, as I believe 

 it would be found highly useful to engineers and surveyors in their 

 general operations ; and I am led to think that the idea has not oc- 

 curred to others from the fact, that upon sending to New York and 

 subsequently to England, for the purpose of the scales being made in 

 horn, it was not without difficulty that the execution of the order 

 was obtained. A short time since a gentleman who has attained 

 to very high honors in the Mathematical sciences in Paris, M. Cou- 

 lon, informed me that the head engineers in France verify the calcu- 

 lation of the area of irregular figures, by cutting out the figures in 

 paper of a known weight. He at once admitted the superiority of 

 this scale, both in accuracy and celerity of calculation. 



I have lately been informed that all the computations of irregular 

 figures in the surveying and drawing branch of the Crown Lands 

 Department have been effected, for some years past, through the 

 instrumentality of this scale. 



Since ofiering this communication to the Institute, it has been 

 stated to me, for the first time, that a similar instrument to 

 that which forms the subject of this paper was, about thirty or 

 forty years since, used in the Government trigonometrical survey 

 of Ireland. 



But I have yet to learn that it is now in general use, notwith- 

 standing its great advantages : the law for its construction allowing 

 of illimitable enlargement and divisibility in regard to scale. 



