A RECORDING MICROMETER FOR ROCK ANALYSIS 231 



Each trial consists of fifteen transepts of the section at intervals of 

 one millimeter, the second series starting one-half millimeter nearer 

 the edge of the section so as to occupy positions staggered with 

 those of the first series. Each transept crosses an average of about 

 ten mineral grains. The measurements, readings, and recording of 

 totals for the transepts were completed for each trial in about 

 thirty-five minutes. 



TABLE II 

 iNSTUtmENT Readings — Trial II 



It will be seen that there is rather good agreement in the results 

 for the three more abundant constituents but less satisfactory 

 agreement in the percentages for the apatite. Considering the 

 scarcity and irregular distribution of the mineral, this result is not 

 surprising and is only to be improved by a much larger series of 

 measurements. 



Although the writer has never used an instrument of the Shand 

 type, he is confident that the instrument here described can be 

 handled with equal facility in any kind of measuring operation and 

 has the important additional advantage of permitting simultaneous 

 estimation of any number of constituents with the resulting economy 



