/ 



28 BOTANICAL GAZETTE [November 



At the base of the mountains the temperature range is from 

 37? 7 to "34?4, though neither of these figures is often reached by 

 thermometers elevated a few feet above the surface of the ground.^ 



The following is the record of maximum and minimum tempera- 

 tures obtained by me during the summer of 1905 : At Boulder (1620"^) 

 from June 21 to July 20 the maximum thermograph reading was 

 34? 4, the minimum 5°. At timber-line during the same period the 



maximum 



maximum thermograph reading was 22?2 and the minimum —3? 9 

 Three miles east of Boulder on the plains (1590"^) the 

 minimum thermometers from June 13 to July 31 gave 

 40? 3 and a minimum of 6?i; from July 31 to Auc 



mum 



of 41*^ and a minimum of g??-"^ The instruments at the cafion 

 mouth (1710^) from June 13 to July 31 gave a maximum of 3 

 and a minimum of 7?7, while those on a moraine (2550"") from 

 August I to August 2g gave a maximum of 30? 3 and a minimum of 

 4? 7. These results show an approximate difference in mean tem- 

 perature of 11^ between Boulder and timber-line, an approximate 

 difference of 1° per 160™ altitude, the difference in the maxima being 

 slightly greater and in the minima slightly less than this. It must of 

 course be borne in mind in the study of these results that they are 

 fragmentary, covering comparatively short periods. 



As already remarked, comparatively little confidence can be 

 placed in the psychrograph records. The curves traced by the two 

 instruments are in no way conformable to each other, owing to the 

 fact that the relative humidity is dependent on such local factors as 

 sunlight and wind and hence is liable to sudden and considerable 

 variations within limited areas. I have even known the temperature 

 recorded by the wet-bulb thermometer to fall i?5 C. w^ithin a few 

 seconds when a sudden breeze sprang up, succeeding a calm. These 

 facts show that a comparison of humidity readings between different 

 stations at any given instant of time is open to serious error, and 



thermomet 



owing to local conditions. 



formation 



5 All temperatures are recorded in degrees Centigrade. 



6 The great difference between the maximum at Boulder and three miles east of 

 Boulder is doubtless traceable to the different elevations of the instruments above the 

 ground at these points. 



