



• • 



V1U 



PEEFACE. 



rical observations made in that part of the State should be carefully revised and recom- 

 puted, with the aid of the table of corrections which we were then able to prepare from 

 our three years' series of observations, which had been specially made in order that we 

 might be furnished with the necessary data for that purpose. 



This part of the work was, therefore, that which first received our attention. The 

 tables in question were computed and published under the title of " Contributions to 

 Barometric Hypsometry, with Tables for Use in California." Then came the laborious 

 operation of recalculating and arranging the barometrical observations at the various sta- 

 tions in the gravel region, the corrections indicated by the tables being applied to them. 

 The method of applying the corrections in question, and the reasons for their use, have 

 been fully explained in the " Barometric Hypsometry," which was issued in 1874. A 

 supplement, forming the fifth chapter of that work, was published in 1878, in which 

 the practical value of our tables is demonstrated, by a bringing together for comparison 

 and discussion of the results obtained by working over the many hundred observations 

 which had been taken in the gravel region. In this division of the work it is shown 

 that the use of the tables in question has reduced the error of the results, on the average, 

 by fifty per cent; and I may here add, after having made a careful examination of the' 

 whole subject, that there is no method of observation by which barometric results can be 

 freed from the class of era 3 which these tables are intended to remove, neither is there 

 any kind of corrections which can be substituted for those furnished by our work. 

 All these laborious computations and investigations of the barometrical data were made 

 by Professor Pettee, or by assistants employed under his direction. It must be noticed, 

 however, that a portion of the altitudes given in the body of this work have not had 

 the tabular correction applied to them. Consequently they differ slightly, in numerous 

 instances, from those published in tabular form in Appendix C, which presents in one 



body the results of all the later and more trustworthy determinations made in the gravel 

 region proper. 



During the time when the earlier part of onr surveys in the hydraulic mining district 

 were being made, we had the work of the three observers at the regular fixed" stations, 

 which we could use in calculating the results of our observations taken at various 

 points in their respective vicinities. During the re-examination, last year, by Pro- 

 fessor Pettee, however, of certain portions of the mining comities, as mentioned further 

 on, he had not, to the same extent, the advantages of corresponding station barometers ; 

 but by skilful combination of observations of the aneroid with the mercurial barom- 

 eter, of each of which kinds he had two, the latter being used as station instruments 

 for short periods at important central points, he was enabled to secure very trustworthy 

 results, probably but little, if at all, inferior in value to those obtained in former 

 years.* . 



* la the Table of Barometric Altitude* (Appendix C), those results to which an asterisk is prefixed are from 

 observations made by Professor Pettee in 1879, as well as some others, M specified in the headings of the groups 

 of localities. All the elevations given in the list of places north of the Middle Yuba are from the same source 









