308 



GEOLOGY OF THE COMSTOCK LODE. 



due to the v.ariation of the barometric pressure or to thewater level appa- 

 rent. 



A series of experiments made with the rock-chamber empty, the rest 

 of the apparatus remaining, however, as before, gave the following results: 



Table XIV. 



The interval of time covered by these experiments is, of course, too 

 small to justify any confidence in tlie constants which might be derived 

 from them. They are, however, sufficient to show that /it undergoes 

 changes analogous to those noted in the preceding pages. It probably fol- 

 lows, therefore, that the final results may be regarded as giving an estimate 

 of the degree of accuracy attainable by the method in its present shape. 

 The chief source of error is the fact that the apparatus does not maintain 

 the constancy of temperature necessary. It is apparently impossible by 

 means of it to heat the large mass of rock to the same temperature through- 

 out. Furthermore, the thermometer employed is neither in sufficiently inti- 

 mate contact with the rock, nor are the junctures placed in circumstances 

 as nearly identical as is desirable. Finally, I am inclined to infer that a 

 stationary thermal condition was not reached in the experiments. Although 

 this supposition accounts for only a part of the anomalies met with, it will 

 nevertheless be necessary in future researches to extend the time of each set 

 of observations considerably beyond the duration of the above experi- 

 ments. I omit a detailed discussion of these matters, however, as a further 

 study of the subject is intended. 



