KELATION OF HEAT AND DRYNESS TO THE LOCUST. 115 
18(34 and 1866 being favorable or unfavorable to the increase and spread 
of the locust ? 
First. That 1804, as regards heat and dryness, was unusually favorable 
for their development, and that the decrease in the rainfall the two 
immediately preceding years, rendered the conditions still more favora- 
ble than they would otherwise have been. 
Secondly. That in 1866 all these conditions were reversed, the rain- 
fall was considerably in excess of the average amount, the season through- 
out the entire Northwest was somewhat colder than in 1864, and the pre- 
ceding year presented these adverse conditions to an equal if not greater 
extent. 
If it be true, as heretofore stated, that unusual heat and dryness are 
both necessary to the excessive development and spread of locusts, how 
are we to explain the apparent contradiction of this theory shown by the 
data presented ? 
So far as the data given relate to 1864, the facts accord with the theory, 
the only cause for surprise being that the invasion of the temporary re- 
gion was not more general. The difficulty isi to explain how those relat- 
ing to 1S66 can be made to accord with it. That the locusts did invade 
Kansas, Nebraska, Missouri, and a part of Texas this year in large 
numbers is a fact that cannot be disputed, and that large swarms ap- 
peared in Montana is also, true ; that the season throughout the entire 
West was generally of a slightly lower temperature and considerably 
more humid than the average is clearly shown by the meteorological 
data given. 
Shall we contend that meteorological records do not always correctly 
indicate the general character of the season ? This would be virtually 
saying that they are of no practical value, a proposition we are unwilling 
to assume. Shall we abandon a theory in reference to the increase of 
insect life which accords with the experience of a thousand years, and 
which no one has ever ventured to dispute ? By no means. Whether 
able to explain this apparent contradiction or not we are not prepared 
to abandon either of these views. 
Before attempting an explanation we will present fuller records of the 
seasons named as given in the annual reports of the Agricultural De- 
partment, and also bring forward the meteorological data relating to 
the great invasions of 1874 and 1876. 
Table III shows the monthly means of rainfall by States, being the 
averages of all the stations in a State. It is from the records in the re- 
ports of the Agricultural Department. 
