19 
change was at this time slightly felt. The main portion came from the 
same districts as on the day previous. There was practically no ad- 
vance of the van, but a filling up of the country already traversed by 
the scouts. 
On the night of March 21, at 11 p. m., an area of low barometer (29.9 
inches) was passing eastward across the Upper Mississippi Valley and 
was central at North Platte, Nebr. It produced SE. winds of moderate 
strength in all the Mississippi Valley except the extreme northern part, 
above La Crosse. The temperature rose throughout the district to 56° 
at Saint Louis and 35° at Saint Paul; but north of this, beyond the in- 
fluence of the SE. wind, it fell rapidly to 18° at Moorhead and 11° at 
Saint Vincent. The isotherm of 40° was carried up to La Crosse. As 
morning approached, the temperature still rose in the northern part 
and the sky became overcast with some local clouds and rain. It was 
a night of much migration, owing to the influence of the area of low 
pressure, which at 7 a. m., March 22, was central at Omaha and Yank- 
ton, where the barometer at 3 p. m. registered 29.74 inches. This was 
a fall at Yankton of .32 inch during sixteen hours, while the center of 
the low area moved but a few miles; and the necessary result was a 
great rise in temperature and consequently great movements among 
birds. But the movements took place only to the east of the low press- 
ure area; for it is a law of atmospheric circulation that the winds are 
attracted from the south, not directly toward the center of the low press- 
ure area, but toward places to the east of it in the same direction that 
it is moving, while the winds which it attracts from the north move 
toward places to the west or behind it. Migration, therefore, would be 
looked for in vain to the south, west,or north of Yankton. The whole 
of this immense movement, which in number of records was as great as 
that of the three previous days together, and in number of individuals 
was many times greater, took place to the southeast and east of Yank- 
ton. The SE. winds prevailed up to La Crosse, and this place also 
marked the limit of the night's movement in that direction. A map 
was made of the migration which took place on this day, and it was 
found to cover a very nearly circular area, 250 miles in diameter,.the 
center of which was midway between Keokuk and Davenport. Some 
idea of the great number of birds which were migrating during this ni ght 
may be had from the fact that at Saint Louis twenty-six different species 
were noted as having arrived or increased. It is well to bear in mind 
that all these birds were migrating on a rapidly falling barometer, hence 
in the face of what is usually considered a sign of an approaching storm ; 
and it may be noted also that all this great movement did not advance 
the van, which remained where it had been before. 
March 23, bird migration was at a standstill. The area of low press- 
ure, which was central at Yankton in the afternoon of the 22d, had 
moved to Saint Paul by 11 p.m., the barometer falling steadily to 29.61 
inches. During the night it moved NE. to Marquette, Mich., falling 
