24 THE ERRORS OF PRECISION. 



approaches the year in which the weighings are actually 

 made. 



Even in the case of coins, we remain ignorant of the 

 exact conditions of this error, depending on the rapidity 

 and character of actual circulation. 



This is precisely the condition which modern chemistry 

 presents to-day in its record of atomic weight determina- 

 tions. The form in which these conflicting results of 

 experiment are usually presented fails to convey a proper 

 appreciation of the magnitude of these differences. 



As it is most important at the outset of this investigation 

 to have a proper understanding of the actual errors prevail- 

 ing, we shall give the necessary details for the most valuable 

 element gold. 



V. ACTUAL ERRORS OF THE MEAN. 



That the mean of a series of atomic weight determina- 

 tions is, de facto, affected with quite large constant errors 

 (constant for each series or process used) can be seen by the 

 examination of any actual chemical set of determinations. 



To make the fact convincing, we select the very noted 

 work of Mallet on the atomic weight of gold. 



This most noted chemical work on the atomic weight of 

 gold was done by Professor J. W. Mallet of the University 

 of Virginia, and first published in the Philosophical Trans- 

 actions of the Royal Society (London) for 1889. 



Through the personal courtesy of the distinguished 

 author I have been able to study the details of this highly 

 important research from an extra copy of the publication in 

 vol. XII of the American Chemical Journal (Baltimore). 



It is almost unnecessary to add that this work of Pro- 

 fessor Mallet is justly considered equal to the best chemical 

 work done in this line of research during the last quarter of 

 a century. By fully making this opinion our own we may 

 be permitted to take the results of this chemical research as 

 representing the best of this kind of chemical work now on 

 record. 



