^8 Chapman 07i NoctuDial Migratio7i of Birds. [January 



be, as a slight contribution to the larger amount of data we 

 must amass before arriving at any strictly accurate conclusions 

 concerning every phase of the nocturnal journey of migrating 

 birds. 



The following notes were obtained with the assistance of my 

 astronomical friend, Mr. John Tatlock, Jr., on the night of 

 September 3, 1SS7, at Tenafly, New Jersey, about three miles 

 west of the Hudson River, Mr. John F. Paulison most courte- 

 ously having placed his observatory and 6|^-inch equatorial tele- 

 scope at our disposal. 



The most important facts to be determined in observations of 

 this nature are, of course, the height at which these flights occur, 

 and also the number of birds which cross the field of view at 

 any given time. 



The method adopted was the same as that used by Mr. Scott, 

 the telescope being pointed at the full moon, which served as a 

 background, showing with wonderful distinctness the birds as 

 they crossed, the observer calling to the recorder as each bii'd 

 came into view, the latter noting the time. 



These observations appear in the following table, where also 

 are given the apparent altitudes of the moon computed at ten 

 minute intervals during the period of observation. 



From the altitudes are computed the heights at which the 

 birds in the field at that time were probably flying. 



The problem of determining this height exactly is not, so far 

 as we can now judge, capable of definitive solution, for the rea- 

 son that we have no means of ascertaining the distance of the 

 bird from the observer. 



In this case, thei-efore, we are compelled to resort to an 

 hypothesis of the probable distance at which a bird was visible, 

 and we thus assumed that the least distance from the observer 

 at which a bird could be seen was one mile, the greatest five 

 miles, feeling sure that, in accepting these limits, we do not over- 

 estimate the greater distance. 



i\\ this connection the appearance of the birds as they crossed 

 the field is of great importance, those which passed more slowly 

 being obviously the ones at the greater distance ; and in this 

 class are included the few possessing some marked characteris- 

 tic of flight which rendered indentification possible ; these 

 were as follows : at S.34 a Grackle, at 9.22 a Carolina Rail, at 



