104 THE PRINCIPLES OF SCIENCE. 



the sum of the approximate numbers 34*70, 52-693, 8o i, 

 is 167-5 within less than 07. So far as I know Mr. 

 Sandeman is the only mathematician who has traced out 

 the rules of approximate arithmetic, and his directions are 

 worthy of careful attention c . Although the accuracy of 

 measurement has so much advanced since the time of 

 Leslie, it is not superfluous to repeat his protest against 

 the unfairness of affecting by a display of decimal frac 

 tions a greater degree of accuracy than the nature of the 

 case requires and admits d . I have known a scientific 

 man to register the barometer to a second of time when 

 the nearest quarter of an hour would have been amply 

 sufficient. Chemists often publish results of analysis to 

 the ten-thousandth or even the millionth part of the 

 whole, when in all probability the processes employed can 

 not be depended on beyond the hundredth part. It is 

 seldom desirable to give more than one place of figures of 

 uncertain amount ; but it must be allowed that a nice per 

 ception of the degree of accuracy possible and desirable is 

 requisite to save misapprehension and needless computa 

 tion on the one hand, and to secure all attainable exact 

 ness on the other hand. 



c Sandeman, Pelicotetics/ p. 214. 



d Leslie, Inquiry into the Nature of Heat, p. 505. 



