CLIMATIC CONDITIONS OF THE UNITED STATES. 153 



of these two points on the chart, by means of a Une passing directly 

 over the mountains, is absolutely certain to be wrong. On the other 

 hand, whether to bend the connecting-line to right or left in passing 

 around the range may not be apparent at all from the data of other 

 stations, so that it might be drawn either way. Whichever way the 

 truth might require the line to be turned, it seems that either way 

 is a better approximation than the method of directly connecting 

 the two datum-points, which we may be sure is incorrect. Usually 

 other climatic factors, known to be related to the one receiving atten- 

 tion, may be used to throw the weight of probability in one direction 

 or the other. 



In our charts we have followed this method of rational guessing 

 and have tried not to pass isocHmatic lines through points where we 

 are practically certain they do not belong. We have also attempted 

 to interpret the various climatic features by as nearly similar criteria 

 as are possible in the nature of the different cases, and have tried 

 to correlate our guesses in regard to related climatic features. The 

 future may be expected to show egregious errors in many instances, 

 but the discovery of such errors may lead to progress. 



After the revision of the charts, by means of the topographic con- 

 tours and hypsometric coloring of the base-map, they were again laid 

 aside and later were carefully scrutinized and corrected where appar- 

 ently necessary, with reference to one another and to a large relief- 

 map of the United States.^ Only after these repeated studies and 

 revisions had been accomplished were the chmatological charts traced 

 upon the generalized vegetation maps, or whatever base maps were 

 requisite, and the lines inked in. 



The charts resulting from the above-described methods of procedure 

 are characterized by very irregular lines in the western part. While 

 we are convinced that many of these western isoclimatic lines are 

 quite probably wrongly drawn (the data at hand are so unsatis- 

 factory and the available stations are of such inadequate number and 

 distribution), yet we think that an attempt to interpret, as far as pos- 

 sible, the scanty information that is available should advance our 

 knowledge of this important subject of chmatological zonation more 

 than would be possible from smoother hues drawn mainly without 

 reference to topography, or from the complete omission of any attempt 

 at a chart of these complex western regions. 



As has been pointed out above, the drawing of isoclimatic lines is 

 frequently a matter of selecting the most probable of several directions 

 and positions, all of which are possible from the standpoint of the 

 limited climatic data. Even mth an excellent series of data, no two 

 workers would place a given line in exactly the same position through- 



1 The "Relief map of the United States," Atlas School Supply Co., Chicago, on which altitude 

 is actually expressed by magnified relief. 



