QUERIES RELATIVE TO THE TENSION OF VAPOR. 
7 
Michler’s station, gave for the elevation of that place above the sea 260.7 feet. The height of 
Lieut. Michler’s station above the water is estimated, and it is probably a few feet higher.* 
These results are believed to he very nearly correct, yet there appears to he some effect upon 
the mercurial column, which is difficult to explain without a long and careful series of observa¬ 
tions. May not this effect be due to the tension of aqueous vapor? The period at which the 
atmosphere on the Pacific coast and the lower region of the Colorado river is most heavily 
charged with moisture is during the winter months—the mean temperature of winter is not 
low ; the tension of vapor is, therefore, comparatively great. Does it not, then, have the effect 
of increasing the pressure upon the cistern, causing the barometer to rise too high? The 
months of May and June being excessively hot and dry, there would he hut little or no effect 
due to the tension of vapor, the pressure indicated being that of dry and highly rarefied air, 
would it not be too low ? The observations of Lieut. Michler opposite Fort Yuma, above 
referred to, uncorrected for abnormal error, give as a mean 29.865, (58° mean air temperature.) 
Ours in June, for the same place, give 29.691, (90° mean air temperature.) The question is, 
which of these results is nearest the truth ? If the tension of vapor has any effect, is its 
increased effect upon barometric pressure in winter in greater ratio than its absence entirely, or 
the decreased pressure due to rarefaction in summer ? It appears to he in a sensibly greater 
ratio at Fort Yuma in winter than in summer. 
After the normal corrections, as it were, are applied to any series of observations, does not 
the residuum include any effect of aqueous tension, if there be such? and if there is no effect 
due to the tension of vapor, is not the pressure during the winter months in the Colorado 
basin, &c., where the mean temperature is about 60°, and the atmosphere nearer its normal 
state, more nearly correct than in summer when the mean temperature is 90° and the reflection 
from the arid plain rarefies the air to so great an extent ? These queries are thrown out by 
way of suggestion, as this question of the effect of aqueous vapor is still open to investigation 
and practice. 
There are a complete set of observations with Mason’s hygrometer, taken in connexion with 
the barometric observations to be found in the general table, and it is hoped that, in the hands of 
an experienced meteorologist, they may throw some weight on this subject. 
To the observations at the various points between the Colorado and Rio Grande, the abnor¬ 
mal error was not applied; for, as above stated, suitable observations could not be obtained 
with which to compare. It appears, however, from the direction of the curve at San Diego and 
Fort Yuma, as late as June, and from the curve of the various camps, that this correction for 
the months of July and August, 1855, did not, probably, exceed plus 0.050. 
For the correction of air temperature ^ ^ ^ the mean monthly temperature, as 
nearly as could be ascertained, was taken for t' instead, as is usual, of taking the temperature 
* The result of 80 observations of Lieut. Michler, in March and April of the same year, at the initial point, 27 miles below 
Fort Yuma, discussed and corrected in the above manner, give the height of the river at this point 156.8 feet above tide. The 
rapid current of the Colorado river, nearly six miles per hour during moderate freshets, can be accounted for by this slope 
of the plain through which it flows. There seems to be some reason in the supposition that this stream flows down in shutes 
from one plateau to another. This appears to be the general rule of all small streams of the Colorado and Gila basins and in 
the Great Basin where I have traveled—the communication from one steppe to another being through a shute or canon caused 
by some great revolution of nature—a cracking due to an upheaving force, or, which is most probaple, to the shrinking of the 
earth’s crust during the cooling process. 
