METEOROLOGY. 



247 



70 



changed to tlie northeast^ and blew "heavily from that quarter for more than twenty-four hours ; 

 during this time the thermometer fell to 1^.5 Fahrenheit^ and snow fell to the dej)thof one inch 

 and a half. 



The cold weather lasted for about three daySj and a most delightful calm succeeded the 

 severest norther noted in the record. A few days after this, the regular observations were taten 

 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 suffi- 

 cient 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 eff'ect of any 

 chano-e 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 Eio 

 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 Fron- 

 tera, 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 eveninjr observation more nearly equal in the different seasons. 



o 



The columns in which are noted the daily means for thermometer and dew-point observations 



e 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, Lut it happened to be the only year when a single observer was 

 stationary for any length of time at the same place. 



