SMITHS! i MAX CONTRIBUTIONS TO KNOWLEDGE VOL. li 



graph of the bird from about its own level coming directly toward or going 

 directly away in soaring flight, are these: 



Approximate weight of the bird, — and approximate tracing of its extended 

 wing with the area, so thai we ran tell the area of the supporting surface rela- 

 tive to the weight, and finally, the distance between CP. and CG 2 , which is obtain- 

 able by the process which T bave explained. 



1 am afraid that what I have just been describing at such length may have a 

 certain obscurity to you. but if you will give me an opportunity, I shall he pleased 

 to illustrate it with the actual experiment when the bird is hung up by a string, 

 and you will see that it is in reality simple. 



Referring to the sketches on page 3 of this communication, a and b corre- 

 spond to the centers of pressure on either wing where the upward pressure of the 

 air distributed over each wing may be supposed to he gathered in a single point. 

 This, as 1 have said, is called the center of pressure with reference to the vertical 

 flight, and its symbol is CP,, while the horizontal dotted line between them repre- 

 sents the level of CP, from the best estimate that I could make when the wings 

 arc in their natural position of soaring. It is evident that this line passed far 

 above the body of the vulture, and if (the corresponding symbol for the height 

 of the center of gravity being CG 2 ), the CG, of the entire bird be taken, it will 

 be found to lie nearly in the point c. Where c is in the present case, I could not 

 determine exactly in my hasty examinations in the live bird, but I assume that it 

 is about \ way between the central horizontal axial line of the bird's body and 

 the upper portion. I repeat that it is important to me to know what the vertical 

 distance is between CP, and CC, in eacb specimen of soaring bird. I may ob- 

 serve in illustration that in the common sea-gull, it is nearly as shown in the faint 

 sketch; thai is to say, that the corresponding line a b in the soaring gull passes 

 distinctly through the upper part of the body, and the distance down to the CCL, of 

 the whole in the gull is almost nil, while in the buzzard it is very considerable 

 as shown by tin responding distance in the " John Crow." 



Now, what I want to get from you is the corresponding figures for an aver- 

 age specimen of our Washington buzzard, [f you will kindly have one killed and 

 weighed while fresh, and before the rigor-mortis has set in, first noting the posi- 

 tion of its wings when soaring in a calm, and (if possible) when coining toward 

 you or going away in about a horizontal plane with your eye, in which position 

 the wings will be elevated and bent somewhat as in the case of the above sketch 

 of the " John Crow "; if yon will kindly do this, so as to give me corresponding 

 facts with reference to the buzzard, namely weight, area of extended wing sur- 

 face, distance between tips as bent up in ordinary flight, distance between c.r- 

 tended tips, /Ac quantity CP,- CG 2 , and also will make such a tracing of the buz- 

 zard's wing as Mr. Manly will show you of the ".John Crow's," I shall be 

 obliged. 



My impression is that the buzzard is a considerably heavier bird than the 

 "John ('row,*' without, however, very much greater spread of wing. I may 

 observe that when the win-- of the Jamaica bird were spread out, they were 

 spread quite to their utmost extent, ami the distance between the tips of the 

 terminal feathers was much greater than when in flight. I wish you would 

 kindly also add the scientific name of the " John Crow," with any particulars 

 that yon would think of interest. 



If there be any special expenses incurred in the preparation of this mem- 

 orandum, including the time of a photographer, I will direct them to be paid 

 from (he Smithsonian fund. 



