458 



SCIENCE. 



[Vol. II., No. 35. 



holding varies with the atmospheric pressure 

 aud temperature. 



While it seems to us that a table showing 

 the relative humiditj-, i.e., the percentage of 

 saturation of the air, would be sutflcientlj' 

 accurate as a basis of comparison, j-et, as it 

 might be objected that such a table would be 

 subject to error, we have appended another 

 table, giving the absolute moisture, or the 

 number of grains of vapor to the cubic foot of 

 air. This second table we have computed 

 from Glaisher's tables. 



Consulting these tables (table I., columns 

 iii. and iv.), it is seen that Denver and Santa 

 Fd afford a ver}' low relative and absolute 

 amount of atmospheric moisture, — a rela- 

 tive amount, which, as between Denver and 

 JacliSonville, is as 1 to 3, and, as between 

 Denver and Los Angeles, is as 1 to 2. 



This proves, that, on the eastern slopes of 

 the Rockj' Mountains, we have, in addition to 

 the favorable element of elevation, a second, 

 that of drj- air, as an element of climatic influ- 

 ence in the cure of phthisis. 



Precipitation. 

 Closely related to the foregoing, is a consid- 

 eration of the mean annual precipitation, or 

 the mean annual amount (in inches) of rain 

 and melted snow. Its bearing on our subject 

 is apparent in several waj^s. 



1. Of the precipitation, a certain part is 

 lost by evaporation, and tends to increase the 

 humidity of the air. This amount will depend 

 upon the amount of moisture in the air, or its 

 degree of saturation, and also upon the amount 

 of the precipitation left upon the surface of 

 the ground to be evaporated. It is evident 

 that the greater the porosity of the soil, the 

 greater will be its absorptive power, and the 

 less the evaporation from it. Such a porous 

 soil is found on the eastern slopes of the Rocky 

 Mountains. Loose, sandy, and gravellj-, it 

 eagerlj- drinks up all the rainfall ; and such a 

 thing as mud is rarelj' seen. 



2. It is well known that pulmonary troubles 

 are most prevalent during ' thaws,' in those 

 places where the snow lies upon the ground 

 in winter. Now, in the district of the Rocky 

 Mountains under consideration, there is, in the 

 first place, onlj' a slight amount of snowfall, 

 so that sleighing is exceptional, and, in addi- 

 tion, the warm sun soon melts the snow, and 

 the thirsty, porous soil drinks it np ; so that 

 the annual ' spring thaw ' of our Eastern States 

 is a res incognita in this countrj^ The writer 

 remembers verj' distinctly several snowfalls of 



fourteen to twent^'-two inches on a level, of 

 which there was not a vestige left in ten da3-s ; 

 and during that time the air was not dull and 

 raw, and there was but little slush. 



3. Further than this, the amount of the 

 precipitation has a bearing upon our subject, 

 as indicating approximately the ability of the 

 invalid to lead an out-of-door life. We shall 

 defer our discussion of this point to a later part 

 of this paper. 



Turning, now, to the tables, we see (table I., 

 column V.) that in Denver the mean annual 

 precipitation for a period of ten j^ears is only 

 14.77 inches in rain and melted snow, — an 

 amount which is onlj' one-fourth of that at 

 Jacksonville, and which, with Santa F6, gives 

 the smallest showing in our range. 



We can therefore add this element of cli- 

 mate to the other two of elevation and diy air 

 as a i3oint in favor of the Rocky Mountains in 

 the cure of phthisis. 



Temperature. 



The writer in Reynold's System {op. cit.) 

 saj-s of this matter of the relation of the tem- 

 perature of climate to the cure of phthisis, " It 

 was formerly supposed that warm climates were 

 beneficial for consumptive patients. . . . But it 

 will be invariably observed that unaccustomed 

 warmth is injurious. . . .What is really required, 

 is a cool, temperate climate, free from great 

 alterations of temperature." Dr. Austin Flint 

 (op. cit.) calls attention to the fact, that " the 

 disease is oftener developed during the spring 

 months and the hot months of summer," when 

 either there is a great deal of moisture in the 

 air, or the debilitating effects of heat are pres- 

 ent as factors. On the other hand, Ruehle 

 saj's that the temperature has " nothing to do 

 with the prevalence of consumption." 



It is known that the effect of heat is to raise 

 the bodj' temperature, to lessen the number of 

 respirations, to quicken the pulse, to lessen 

 the digestive powers and the appetite, to di- 

 minish the excretion of urea because of the 

 diminishing of the ingesta, and to depress the 

 nervous system, especiall3' if the heat be ac- 

 companied with excessive moisture. It seems, 

 then, that it can be stated as a fair inference 

 from the foregoing, that a dry, temjjorate cli- 

 mate is to be sought by the phthisical invalid. 

 The Jlocky Mountains furnish a dr\' climate. 

 The table (table I., column vi.) shows that the 

 mean temperature is nearlj- a mean lictwecn 

 the extremes in our range. The question will, 

 however, be presented in a better form far- 

 ther on. 



