198 ENVIRONMENTAL CONDITIONS. 



forms, it follows that the duration of relatively high temperature may, 

 in some cases, be a limiting vegetational condition. It has therefore 

 seemed worth while to attempt a cartographical study of this feature. 



The temperature observations that have been carried out by the 

 Signal Service and by the United States Weather Bureau have already 

 resulted in an enormous mass of data. From our present point of view 

 these data are very unsatisfactory in many respects. The distribution 

 of the stations of observation is, as has been remarked previously, 

 exceedingly unequal, and seems to have been the result of political 

 rather than of scientific interests. Furthermore, the exposure of the 

 thermometers at the various stations follows no general rule; some- 

 times the instruments are placed on the tops of high buildings, some- 

 times near the ground; they are seldom in the open country, and are 

 almost always subjected to whatever peculiar conditions prevail in or 

 over cities. Nevertheless, in spite of the many quite obvious funda- 

 mental errors which a more rational guidance might have been able to 

 avoid, the faithful labors of the observers and interpreters of the 

 Bureau have resulted in a very valuable mass of statistical information 

 upon temperature conditions, and it is from this alone that informa- 

 tion such as we require may be obtained. Especially valuable to us is 

 the Herculean work of Professor Frank H. Bigelow, who has done what 

 was possible to bring order and meaning out of the chaos of existing 

 observations. 



In the present instance, as also in the next following, we have drawn 

 our fundamental statistics directly from Bulletin R of the United 

 States Weather Bureau.^ In this bulletin Bigelow has presented the 

 normal daily mean temperature for every day in the year for 177 sta- 

 tions in the United States. Although the introductory statements of 

 this work are none too clear as to the sources of the temperature data 

 used in the computations, it is implied that these normal daily means 

 are the direct outcome of a graphically mathematical treatment of the 

 normal monthly mean temperatures as given in Bulletin S of the 

 United States Weather Bureau.^ Since, however, the fist of the last- 

 mentioned bulletin comprises but 123 stations, it is obvious that other 

 data than these have been employed in the preparation of the daily 

 normal means. It thus appears that the fundamental homogeneous 

 reductions for at least 54 stations have never been published and that 

 these have nevertheless been made use of in the preparation of the list 

 of 177 stations which we are to employ. While there can be no rational 

 doubt of the approximate reliability of all the data given in the first- 

 mentioned of these two publications, it is to be regretted, where there 



1 Bigelow, Frank Hagar, The daily normal temperature and the daily normal precipitation 

 of the United States, U. S. Dept. Agric, Weather Bur. Bull. R, 1908. 



* Bigelow, Frank H., Report on the temperatures and vapor tensions of the United States, 

 reduced to a homogeneous system of 24 hourly observations f or the 33-year interval 1873- 

 1905, U. S. Dept. Agric, Weather Bur. Bull. S, 1909. 



