The Flight of No:turnal Lepidiptera 55 



In every case the partial coefficients are smaller than the cor- 

 responding total coefficients, owing to the fairly high correlation be- 

 tween the weather factors themselves. The following conclusions may 

 be drawn from a study of the partial coefficients. 



1. Temperature and humidity are much more closely correlated 

 with size of catch than pressure, the two partial coefficients for the 

 latter being smaller than their probable error. , 



2. Temperature has a positive influence on the catch at all times, 

 but the influence is much larger below than above optimum humidity. 



3. Humidity is by far the most important factor studied. Any in- 

 crease in the 7 p.m. humidity up to about 54 per cent tends to increase 

 the catch, while beyond this value it decreases the catch in almost the 

 same proportion. 



4. The coefficients of multiple correlation (designated by large R) 

 for the two sets of data have been computed, which give the total 

 amount of correlation between any factor and all others at once. Their 

 derivation and use will be found in Yule (6) and will not be discussed 

 here. These coefficients are included in Table IV. They are of approxi- 

 mately equal value, both less than 0.50, indicating that about half of 

 the factors influencing the catches have been neglected in this study. 

 Among these might be mentioned wind velocity, moonlight, and pre- 

 cipitation during the daylight hours, which undoubtedly have consider- 

 able influence, considered collectively. 



The writer is not at all satisfied that the method of partial correla- 

 tion is the best possible method of determining the relative values of 

 the factors involved, owing primarily to the assumption of linearity of 

 relationship between the factors, but it at least represents a consider- 

 able advance over the method of estimating these relationships by in- 

 spection of a graph. The correlation coefficients are not in any sense 

 an accurate measure of this relation, but they are at least a relative or 

 qualitative measure, and must be so interpreted. 



LITERATURE CITED 



1. Lugger, Otto, 1896. List of owlet-mioths taken on sugar at St. Anthony 



Park. 1st. ann. rcpt. State Ent. Minnesota, for i8g5. Minneapolis, 1S96. 

 pp. i42-i47. 



2. Dewitz, J., 1911. Bearbeitung der Literatur der Traubenwickler, Nr. 2. 



Bericht der Konigliche Lehranstalt fiir lVein=, Obst=, nnd Gartenbau zu 

 Gcisenhcim am Rhein fiir das Etatsjahr 191 1. Berlin, P. Parry, 

 1912. pp. 218-277. 



3. Dobrovljansky, V. V., 1913. (Pests of fields and orchards according to 



observations made at the Kiev Entomological Station in the year 1912.) 

 Published by the Entom. Station of Kiev, of the South Russian society 



