4 
REMARKS ON METEOROLOGY AND BAROMETRIC RESULTS. 
difficult to determine on account of its variableness, and which is probably due, in part, to a 
want of perfect adjustment, at the time of observation, of the index point; partly to personal 
error, and in part to the unequal bore of the tubes, causing an increase or decrease of capillary 
attraction, for it not unfrequently happens that two barometers, at a pressure of about 30 inches, 
will read with a given difference uniformly ; but when subjected to a less pressure—27 inches, 
for example—other things being equal, this difference will often vary as much as 0.010. This 
fact is observable even during the diurnal range of the barometer, though to a less appreciable 
extent. 
The correction for horary oscillation was obtained from frequent hourly observations taken 
for that purpose. Those used for determining the hourly corrections for the hours of *the day, 
to apply to observations made in connexion with the survey, are given in Table No. 1. In 
Table Ho. 2 are the observations for the twenty-four hours at the places indicated. For the 
construction of these curves, see Plate 1, Figs. Nos. 1 and 2. By reference to these tables and 
diagrams, it will be perceived that this phenomenon is marked by irregular oscillations as to 
the maximum and minimum point. This is probably due to the peculiarity of the season of 
winter on the California coast, it being the period when greater fluctuations of the atmosphere 
take place, and also to the want of a sufficiently long series of observations. In several instances, 
during remarkable changes of atmospheric condition, the diurnal oscillations were completely 
broken up. An example of this occurred on the 1st and 4th of January, 1855, at Camp 14', at 
the headwaters of the Salinas river, when a great storm occurred. For a comparison of this 
storm at several other places along the coast, see Plate No. 5. At Camp 17, January 16 and 
17, the atmosphere was in a remarkably quiescent state, and the curve for those days is 
probably very near the true measure for the time and place, the tropical hours occurring at 
10 a. m. and 4 p. m. —(See Plate 1, Fig. 3.) 
The correction for abnormal oscillation, by far the most important element of error in barometric 
discussion, and hitherto the most difficult of measurement, was obtained by a careful comparison 
of nine months’ daily simultaneous observations at Benicia barracks and at the mission of San 
Diego, taken under the direction of the medical department of the United States army, with those 
taken during the progress of the survey. * This comparison was made in accordance with the 
plan of Captain A. W. Whipple, to whom the credit of the suggestion with reference to the 
determination of barometric heights is due, and its results are satisfactory and confirmatory of 
the plan pursued by him in the discussion of the meteorological observations pertaining to his 
exploration near the thirty-fifth parallel. The diagrams (Plates Nos. 2—10) will illustrate the 
intimate relations of this abnormal effect upon the mercurial column for places widely remote. 
By a combination of the observations at the above named places, and with those along the line 
of survey, a scale of correction was obtained, which, when applied to each observation, has 
produced interesting and accurate results. The manner in which this combination was made 
may be briefly stated and the plates explained. The Benicia and San Diego observations for 
nine months, from October, 1854, to June, 1855, inclusive, were plotted in their relative posi¬ 
tions; the hours being by regulation, sunrise, 9 A. M., 3 P. M., and 9 P. M. These were sufficient 
to indicate the direction of the curve of pressure from one day to another ; a line was therefore 
* There is a paragraph on this subject in Kaemtz Meteorology, p. 292, where the sensible parallelism of the curves is 
recognized, but no satisfactory results are given, nor any reference to their application to obtaining correct altitudes for an 
extended barometric profile. 
