“Each circle represents the field of observation as seen through the telescope when focused on the moon. Each line in the circle represents the flight of one bird, the heavily shaded end showing the direction toward which the bird is flying. The broken lines represent the flight of birds that appearedout of focus. (T)aken at Beloit, May I2, 1900.”
“The migration of birds.” Bulletin of the Wisconsin Natural History Society. v.2. 1902.