Bihlioyi-aphical Notices. 219 



for the year mentioned was $33,379,603 gold and $41,110,957 

 silver, a total of $74,490,020 (coining value). The compilation 

 and tabulation have been made under the direction of a special 

 expert, Mr. Albert Williams, jun. The methods followed in com- 

 pilation and in the classitication of mines and of reduction-works 

 are first given. Then the statistics of the Pacific division : — Cali- 

 fornia, Nevada, Utah, Arizona, Idaho, Oregon, Washington, and 

 Alaska. Statistics of the Ilock3--]VIountains division : — Colorado, 

 Dakota, Montana, New Mexico, and AVyoming. Statistics of the 

 Eastern division. Resume of reduction statistics. Coinage. Con- 

 sura])tion in the Arts. Other estimates. Bullion-product of the 

 World. 



Colorado produces 40 per cent, of all the silver of the United 

 States, but only 8 per cent, of the gold. California yields half of 

 the gold, but less than 3 per cent, of the silver. The production of 

 the precious metals in proportion to population, ranging from one 

 mill ($0-001) per head in Alabama, to $278-14 in Nevada, shows 

 with precision how far " mining is a factor of wealth in the several 

 localities." The product per square mile varies from 1 cent for 

 Alaska to $185-20 in Colorado, " the intermediate average forming 

 another standard of developed richness ia the precious metals, from 

 a diff'erent point of view, but roughly corresponding to that of the 

 relation of production to population." The average fineness of gold 

 for the United States is fixed at -876, the placers pi-oducing "over 

 $100,000 of silver annually in alloy with the gold— an item 

 hitherto disregarded by statisticians." Very clear, definite, and 

 elucidative coloured diagrams illustrate the production- and distri- 

 bution-tables above noticed. 



8. A new method of measuring Heights by means of the Baro- 

 meter, by Mr. G. K. Gilbert. This is a complete memoir, resulting 

 from the author's experience in geographical work which he was 

 obliged to take in hand when making the necessary maps for geo- 

 logical surveying in unmapped territories. The new method of 

 hypsomctry is so simple and direct that it has been adopted by the 

 United States Geological Survey. Three barometers are used instead 

 of two ; two arc placed at points where the heiglits are known, and 

 the third is read at the point to be determined. " Urom the read- 

 ing of the two barometers at the points of known height tlie weight 

 of the intervening air-column is deduced ; and, both the weight and 

 height of the column being known, its density is computable. The 

 density thus derived is then used in the computation of the height 

 of a second column of air contained between one of the known 

 points and the point to be determined."' In explaining this im- 

 portant barometrical discovery, Mr. Gilbert treats in full of the 

 barometer and the principles on which its use is made practical ; 

 and of modifying conditions in the relation between air-pressure and 

 local heights, such as density, temperature, and humidity ; and of 

 the resulting " atmospheric gradient," diurnal, annual, and nou- 



