66 CLIMATIC CAUSES AFFECTING THE DISTRIBUTION 
I might, of course, have gone further N. than Leeds and 
Liverpool, but the latter represents the climate of our own 
district (Bidston Observatory being in Cheshire), and Leeds 
the climate further inland and somewhat to the N.E. Taking 
then the mean maximum temperature for the three summer 
months of June, July, and August, for the five last years 
(1878-82), I find the averages to be as follows :— 
Blackheath. Plymouth. Leeds. Liverpool. 
69°.5 66°.4 68°.1 64°.2 
So that we find Blackheath to be hotter than Plymouth by 3°.1, 
and Leeds not only hotter than Liverpool by nearly 4°, but 
actually hotter than Plymouth, nearly 250 miles further south, 
by 1°.7! And as these differences may seem trifling to those 
who are not accustomed to compare mean temperatures, it may 
give them some idea of what they mean when I say that the 
difference between the decidedly warm summer of 1878, and 
the extraordinarily cold summer of 1879 (these being the two 
extremes in the five years), was only 4°.2 on the mean maxima, 
while the average difference between Liverpool and Blackheath 
38,65 Ge! 
We may therefore take as established the following facts, 
which indeed no Meteorologist would dispute, viz. :— 
1.—That the West of England has a moister atmosphere 
and greater rainfall than the E. 
2.—That the day temperature in summer increases rapidly 
from N.W. to 8.E. 
Now I have already shown that the number of species of 
Butterflies also increases rapidly as we go from N.W. to S.E., 
and I therefore submit that until reasons be shown to the 
contrary, we are justified in considering that there is a direct 
connection between the two sets of facts. 
Tt remains to be considered why a moister and colder climate 
in summer should diminish the number of Lepidoptera. And I 
must be allowed here to express my satisfaction at finding that 
so experienced an Entomologist as Mr. B. Cooke has inde- 
pendently arrived at almost the same conclusions, as shown 
in a paper read by him before this Society (Lancashire and 
Cheshire Ent.) last year. In a paper I read before the Chester 
Society of Natural Science in 1875, I suggested that insufficient 
ripening of the wood of trees and shrubs from want of solar 
heat would produce a condition of the leaves injurious to the 
health of the larvee, and I enlarged on this in another paper 
read in 1876. But as these papers were not published (except 
possibly in the local newspapers), and have been in my 
possession ever since, Mr. Cooxe could not have seen them— 
moreover he attributes the unwholesome condition of the food to 
excessive rain, which undoubtedly is a most important element 
in that respect. 
