28 HISTORICAL INTRODUCTION. 



And in all such cases the knowledge of the ori- 

 ginal experiments will put it in the power of the 

 reader to calculate for himself, and to correct any 

 errors into which I may have inadvertently fallen. 

 The want of this attention in other writers has 

 sometimes been severely felt by me, when an 

 arithmetical error was conspicuous, without the 

 requisite data for correcting it, or the means of 

 knowing upon what number the error had fallen. 

 Even the writings of Berzelius, though in gene- 

 ral his numbers are very accurate, are not always 

 free from this provoking uncertainty. 



