631 



dry thermometer is found on the horizontal Hne and the amount of differ- 

 ence on the perpendicular scale. If the two lines, starting from these 

 points in the scale, intersect at the right of the curved line which represents 

 the nocturnal frost curve, i. e., intersect among the dotted lines of the scale ; 

 then no night frost is to be feared. If, however, the point of intersection 

 appears at the left of the hypothenuse of the triangle, i. e.. outside the 

 dotted lines, night frost may be expected with certainty, in case the weather 

 does not change suddenly and warm air currents do not cause the formation 

 of mist or clouds. If, for example, in the afternoon, we find 8 degrees C. 

 on the dry instrument and 4 degrees C. on the moist thermometer, this 

 gives a difference of 4 degrees. The point of intersection of the perpen- 



Frosty Nights 



O ] Z 3 ^ 5 6 7 8 9 fO ti 7Z J5 74 15 

 Height of the dty Thermometer 



Fig. 150. Curve for finding night frosts; according to Dr. Lang, Municii. 



dicular temperature line 8 with the horizontal line of a difference of 4 

 would be outside the dotted lines, i. e., at the left of the nocturnal frost 

 line; therefore a night frost would be probable. 



Hardy Fruit Varieties. 



The more we recognize how manifold are the often outwardly imper- 

 ceptible changes due to frost, which becomes apparent only in their after 

 effects, the more important becomes the search for varieties of fruit 

 resistant to frost. If, however, we compare the experiences of fruit grow- 

 ers, it becomes evident that the climatic conditions of different regions may 

 modify the character of the variety in such a way that a variety recom- 

 mended in one place as hardy is susceptible to frost in another, because of 

 earlier development or lesser maturation of the branches. On this account. 



