474 ]Visconsm Academy of Sciences, Arts, and Letters. 



except v/ith great cirenmspcction and within proper limits. 

 These limits having been found by an investigation of the 

 probable error, such a formula, although useless elsewhere, can 

 be used conveniently in the cases and within the limits where it 

 offers the advantage of brevity and still affords sufficient preci- 

 sion. 



