THE MEAN* WEIGHT OF A SILVER DOLLAR. 



The 200 silver dollars weighed bear as years of coinage 

 numbers from 1878 to 1899, extending over 22 years. Sixty 

 one of these coins bore one of the three years 1889, 1890 and 

 1891 ; their mean year of coinage therefore is 1890. Sixty 

 eight of the 200 silver dollars weighed were coined in the 

 six years from 1879 * J 884 inclusive. 



In the nine years here specified, 129 of the 200 silver 

 dollars were coined, leaving only 71 coins to the 13 years 

 not specified. 



Roughly speaking we may say that in the number of coins 

 in circulation the three years 1889-1891 and the six years 1879 

 to 1884 and aH the other thirteen years not herein included 

 have furnished a nearly equal number of silver dollars, 

 namely respectively 61/68 and 71 for each of these groups, 

 This gives about 20, 10 and 5 for each single year of the 

 groups of years specified. 



This is a much greater variation in frequency than could 

 have been anticipated. 



The Mean a Lower Limit. 



Since evidently abrasion lowers the weight of a coin in 

 circulation, every weight of a coin is below its true legal 

 weight and every mean will therefore also necessarily be 

 below the weight fixed by law for the silver dollar coin 

 (within the tolerance). 



In this case, the mean weight of the actual coins in circu- 

 lation can never furnish the true weight of the silver dollar. 



The true weight of the silver dollar at the time of coinage 

 is evidently the mean weight in actual circulation increased 

 by the loss due to abrasion in circulation. 



In other words, the actual weight determined by weighing 

 the coins in circulation, and any means of such weighings, 

 give only a lower limit* of the true weight of the coin. 



Amount of Abrasion. 



Now, the 68 silver dollars coined between 1879 and I &H 

 gave the mean weight 26.288; their mean year of coinage 

 is i88i>. 



* On that fact rests our method used in the True Atomic Weights, 1894. 



