92 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
a storm they simply disappear from view as the clouds obscure the sky. But if a 
wind adverse to their course meets them they come down in large numbers. The 2d, 
3d, and 4th, up to 3 p. m., were nearly or quite clear and wind continued southerly. 
18C8, August 8, 10, and 11. — Each day much the same calm, but few clouds in the 
forenoon, and immense swarms passing from south to north ; but each day from 1 to 3 
p. m. a northwest to north wind from strong to fresh brought them down like a hail- 
storm. 
Many memoranda were made of flights and arrivals from 18G8 to 1875 too lengthy 
to copy, but all to this general effect : They were invisible when passing over-head 
until near 9 o'clock a. m., or in the afternoon much after 3 o'clock. They must be 
nearly in a line with the sun to be visible, and the sun falling below this angle of 
some 45° leaving untold myriads of them in the air ; yet I never knew them to come down 
after that time (unless driven down by an adverse wind). Again in June, 1875, from 
the 13th to the 24th, on every day, if the sun shone out, they were passing over, but 
none were seen descending at night. The locust rarely moves much in the morning 
till the sun warms up the air as also the locust, and I have no record or recollection 
of their rising till from 9 a. m. to 11 a. m., yet the mass above would be seen by or 
before that time high up on their regular course. Such immense masses could not de- 
scend each night without literally covering or burying the ground. 
Does the main army continue its march night and day, only dropping a few 
stragglers as they become too weary or hungry to keep up f 
1 b. August, 1868.— On the 8th, 18th, 19th, and 20th, days of flight, the thermometer 
ranged from 57° to 86°. 
July, 1875. — From the 13th to the 22d the maximum temperature was from 70° to 
94°, the minimum from 52° to 66°. 
June 14 and 16. — The flight was from northeast to north on northerly winds; 57° to 
79°. 
August 24 to 28.— Northeast wind; 59° to 86°. 
August 29. — Wind south, immense numbers ; 74° to 86°. 
I do not think they rise to join the crowd above (I never knew them to rise unless 
there were swarms passing over at the time) in cloudy weather. Still, when in regular 
flight I do not think clouds stop them, although it obscures them from view. As the 
sun has appeared through broken clouds I have often seen them passing, while when 
the sun was obscured they were invisible. 
1 a and c. Invariably in the direction of the wind, be its force more or less. 
1 c. By arranging the focal distance of a spy-glass at a known horizontal distance, 
and comparison of appearance, and size of locusts; I think the passing swarms are 
from $ to 1 mile high, varying at times, probably seeking currents of wind of greater 
or less velocity. In case of sudden or heavy rains, when the air was full of them, none 
of consequence came down with the rain. It seems impossible that they could fly 
through the storm. Do they rise above it ? In heavy swarms my glasses show them as 
dense as they can move without interference. 
The extent of the swarm it is difficult to ascertain, as the observer can only see a 
small belt. They may extend indefinitely right or left. During the flight from June 
15 to 25 of 1875, I telegraphed east and west. I found a continuous line moving 
northward of 110 miles, and then somewhat broken 40 miles farther. The movements 
of the winds for five days (15th to 20th) averaged about 10 miles per hour; and the 
locust evidently moved considerably faster than the wind, at least 15 miles per hour. 
The swarm I estimated at from one-quarter to one-half mile deep. It seemed like pierc- 
ing the milky-way of the heavens ; my glass found no limits to them. They might 
have been a mile or more in depth. They were visible from six to seven hours of each 
of the successive five days, and I can see no reason to suppose that their flight was 
checked during the whole five days. If so, the army in the line of advance would be 
120 hours by 15 miles per hour = 1,800 miles in length, and say at even 110 miles in 
width, an area of 198,600 miles ! and then from one-quarter to one-half mile deep. 
This is utterly incredible, yet how can we put it aside ? 
