E.-Table of Latitudes and Longitudes-Continued.

*Since this point was established, the corresponding observations at Greenwich observatory have been furnished in manuscript by Prof. Airy, Astrono nomer Royal; and the result deduced therefrom is 7h. 23m. 35s.3, showing a difference of 11s.2 from the adopted longitude.

+ Moon culminations also observed by Salazar, and resulting longitude found to correspond.

W. H. E.

CHAPTER IX.

METEOROLOGY.

SIR: The meteorological notes taken during the march from San Antonio to El Paso, during the latter part of 1850, though sufficiently interesting of themselves, do not furnish data for averaging the temperature, &c., and therefore cannot be recorded in the same form as that adopted for the publication of observations taken at a fixed observatory.

The principal and most interesting portion of the observations is the result deduced and embodied in the barometrical profile of the road already prepared.

The record of both wet and dry bulb thermometers was carefully kept. The highest degree noted was on the 23d October, 1850, at 3 P. M., eighty-four degrees; while the lowest was at sunrise of the 6th of December, of the same year, when the mercury fell to 10.5 Fahrenheit. These results are interesting only so far as noting these two extreme points. From the nature of the marches made, it was impossible to note with any regularity the daily change in any of the instruments.

The chief phenomena noted are those of a local character. The effect of the different ranges of mountains and the long succession of arid plains upon the condition of the atmosphere is shown by the markings of the hygrometer. In passing from the shores of the Gulf to San Pedro, or Devil's river, but little change takes place the same succession of dews, the usual quantity of rain, and, indeed, all the characteristics of a climate enjoying its proper share of humidity are met with. The clouds of the usual forms, cirrus and nimbus, float about, and nothing as yet gives notice that we are approaching a different country. One single day's march, and this is perceptibly changed. The summit of the valley of the San Pedro reached, the hygrometrical condition of the atmosphere is altered at once, the appearance of the vegetation is different, and the whole face of the country shows the effect of the diminution of moisture so accurately and so immediately pointed out by the hygrometer. We cannot speak with certainty of the effect of the change on any of the instruments except the hygrometer; but that the barometer is seriously affected there can be no doubt, though to what extent can only be told by more perfect unhurried examinations. The observations point out the existence of such a change; they show, too, the line of country at which the change commences; and it only remains to fix the exact amount of correction to be used, to make the barometer as useful in these regions as in those countries bordering on the seacoast, or where the great lack of humidity is not so sensibly felt.

During the march, there was experienced a norther of the most perfect character; this occurred on the 4th and 6th of December, and it was at the latter date that the lowest temperature was noted.

The norther commenced at 4 P. M. of the 4th December, and was preceded by no change by which its approach could be predicted. A calm, pleasant day, with the thermometer ranging

from 40° to 70° Fahrenheit, was ended by a sudden rising of the wind from the southwest; this changed to the northeast, and blew heavily from that quarter for more than twenty-four hours; during this time the thermometer fell to 10.5 Fahrenheit, and snow fell to the depth of one inch and a half.

The cold weather lasted for about three days, and a most delightful calm succeeded the severest norther noted in the record. A few days after this, the regular observations were taken up and continued at San Elceario and Frontera; those results, reduced for one year to the form adopted for publication, will be more interesting than these under discussion can be made.

The appearance of the clouds varies so little that it forms no meteorological feature of sufficient importance to be accurately noted. The changes, as might be expected, are from the forms in which a certain degree of moisture necessarily enters to those in which the appearance is that of a fleecy mass of cotton without shape. These last are so far removed from the earth's surface as to be almost entirely out of the influence of the currents of wind indicated by the weather-vanes. Their formation seems gradual, and the increase in size is apparently due to a decrease in the distance. They came and vanished sometimes from the same spot in the heavens; and for weeks together scarcely one "direction" due to the course of the wind could be noted. In watching them carefully, their volume would seem to be lessened or increased, and yet the parts detached could not be seen to float away, nor was there any approach of additional vapor to be seen by which the size of the cloud could be increased.

The character of the winds, with their force and direction, was carefully noted; in particular their effect on the barometer was the subject of repeated observations. The results of these observations are more accurately noted in another place. And though the effect produced was first noticed on the march, yet subsequent observations at the fixed observatory only served to strengthen and confirm the opinion which was at that time advanced as to the effect of any change from east to west, or vice versa, on the barometrical column.

The records of the observations taken at the fixed observatories at San Elceario and Frontera are given fully for one year. These observations were made in the immediate valley of the Rio Grande, and show the changes in the different instruments noted. With regard to the value to be placed on the observations for humidity, it should be observed that the time embraced in the record was one of great freedom from moisture, both at the points observed and at situations on the river far above the observatory. The river during the summer of 1851* was nearly dry in several places in our immediate vicinity, a slight current only marking its progress near Frontera, while its bed served as the best road thence to El Paso.

The chart prepared to accompany this report shows at a glance the most important results deduced from our observations.

The results given in the separate columns of the tabulated forms are deduced from six daily observations, viz: at sunrise, 9 A. M., noon, 3 P. M., sunset, and 8 P. M. During the long days of summer this last hour was changed to 9 P. M., thus making the interval between sunset and the time of the last evening observation more nearly equal in the different seasons. The columns in which are noted the daily means for thermometer and dew-point observations

* The year 1851 was notoriously a dry year in all the northern States of Mexico, and so far the selection of that year is unfortunate as affording a measure of the average rain, but it happened to be the only year when a single observer was stationary for any length of time at the same place.

W. H. E.

will, of course, present different records from those which would have been shown had the results merely been deduced from the two daily extremes of heat and cold, or the dew-points calculated from those observations only.

In addition to all these observations, the 21st day of each month, as the regular meteorological term-day, was carefully noted by the record of observations for each hour of the twenty-four. The remainder of the meteorological data serves in a great measure merely for the calculation of the elevation of points on the line of survey or travel. These results will be found embodied in the different profiles of the country over which the line passed.

The observations of 1855, by a careful comparison with others of the same character, taken simultaneously at different places, have enabled me to establish the height of the initial point of the boundary on the Rio Grande in a manner that must be more satisfactory than any yet adopted.

This elevation varies slightly from that of El Paso.

In the computation for elevation I have used the French formula of Delcros, and have employed some other corrections consequent upon the value of horary variation, founded on the observations for that quantity taken at San Elceario. In most instances, however, the points of observation were too remote from the fixed observatory for the horary correction to be of any great value. In these the usual corrections for temperature, &c., only were used.

The effect of the direction and force of the wind on the mercury of the barometer has been referred to above, and I mention it here only to state that my observations on this subject were sufficient to assure me of the great necessity of noticing these values in connexion with the barometer more particularly when observations are being made for altitude. The exact value of the quantity I have not ascertained, but that it exists I am confident; and I trust that future and more prolonged observations will fix the value in a manner sufficiently accurate for its use as a correction in barometrical computations.

All of which is respectfully submitted by your obedient servant,

MARINE T. W. CHANDLER,

Assistant in charge of Meteorological Department.

Major WILLIAM H. EMORY, 1st Cavalry U. S. A.,

Commissioner United States and Mexican Boundary Survey.

NOTE.-Of the immense mass of materials collected, showing the meteorological character of the country adjacent to the boundary line, I have deemed it proper to produce here only a short abstract from the tables. Those who may desire further information can obtain it by reference to the records filed in the Department of the Interior.

W. H. E.