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Show 49 nal records by the cnief of party, assisted by the barometric observer, and as soon as the book is filled, it is forwarded to the office, with his certificate that it is a true copy. Form VI is for fhe computation of altitudes from synchronous observations of barometer, thermometer, and psychrometer at two stations. It is made to conform to the tables in the appendix of Colonel Williamson's paper on the " Use of the barometer, & c." It needs no description, and is not inclosed herewith. For the field, then, we have three books of record, ( Forms I, III, and IV,) sexigessimo in size, and two books for transcribing and duplicating these, ( Forms II and V,) of quarto form. The meteorologist has simply to read all the instruments at the hours prescribed and record the observations, to furnish the reading of his barometer and attached thermometer when demanded, and afterward, at times prescribed by the chief of party, to transcribe all records, as he finds them, upon Forms II and V. OFPIOE- COMPUTATION OF ALTITUDES; ANEROID BAROMETERS AND PROFILES. In the office- work, I have been ably and efficiently assisted by First Lieut. Rogers Birnie, First United States Infantry; Hospital- Steward T. V. Brown, United States Army; and Mr. F. M. Lee; and by the exertions of these gentlemen the work is nearly up to date. The order in which this work has been performed, and its character, is as follows: 1. The comparisons of instruments at Washington, D. C. and Pueblo, Colo., were reduced, and the error of each instrument at the date it left the rendezvous- camp at the later point determined. 2. The field- transcripts of the various parties were examined, the records of the instruments traced, the standard barometer and its error at each comparison determined, its readings corrected and reduced to 3* 2° Fahrenheit, and, by comparisons with its reading and that of its attached thermometer, the errors of indices of all other instruments determined, their readings corrected thereby and reduced, and the force of vapor and relative humidity from psychrometric observations compnted. 3. All hourly observations taken by the various parties were corrected for instrumental errors, reduced to 32° Fahrenheit, and erratic observations corrected, copied upon the hourly forms, and reduced to level by Colonel Williamson's second method, and horary tables formed, which, in connection with the barometric records at the main astronomical stations, gave us twelve tables of horary corrections in or adjacent to the area surveyed in 1874, for altitudes varying from 4,500 to 8,600 feet, within which limits nearly all the aneroid work, in connection with which the tables were principally used, is included. 4. Observations taken at hours differing from those of the Signal- Service, and all aneroid observations, were either corrected by interpolation or Dy the horary tables, and the means of barometer reduced and relative humidity taken. 5. The observations taken by the Signal- Service of the Army at Denver, Colorado Springs, and Santa Fe\ for the time our parties were in the field, were transcribed, and these stations referred to each other by means of the six months' series, and the altitudes of the two last mentioned reduced.* €. The altitudes of all camps and stations where cistern- barometers were read for a number of days were computed by referring them, by the mean of the series, to synchronous observations at the nearest of the signal- stations, and, of all camps and other points where isolated observations were taken, were deduced either from synchronous observations or from daily means; the observations having been corrected for horary oscillation, and referred either to our semi- permanent camps or to the Signal- Service stations mentioned. These determinations number over seven hundred. 7. The altitudes of all aneroid stations were computed on Form V wherever a continuous series of observations and comparisons with cisterns were found. Isolated readings, when comparisons have not been made for several days, and where subsequent and anteror comparisons do not show a nearly constant index- error, have been almost always rejected as unreliable for absolute altitudes, but have in many cases been computed on Form VI for the information of the topographers in constructing their maps. The altitudes from this source which have been computed number between three and four thousand, and give continuous profiles along about ten thousand miles measured and meandered lines. 8. Upon the completion of the computation of altitudes, all cistern- barometer deter- * The altitude of Colorado Springs is well known from actual leveling; but upon comparing with the Signal- Office barometer at Santa Fe\ I found reason to believe that its error is different from that given by the Signal- Office. Fearing that the same might be true of one of the barometers at the other stations, I preferred to use the relative altitudes as given by the six months1 barometric observations referred to each other to the rigid level- lines. It is susceptible of easy demonstration that if the barometer at either of the intermediate stations has a very appreciable undetermined error, this coarse is the best for all observations referred to that station.-( W. L. M.) |
