Sir,

I am induced to address you on a subject that I notice has occupied your thoughts when writing your work: “Voyage around the World”¹

Speaking of the flight of the Condor, and its wonderful power of sustaining itself in mid-air apparently without motion of its wings. I notice that you as well as others who have spoken of it do not take into account the fact that the wind is always blowing more or less strongly while this phenomenon (if we may call it so) shows itself.² I take it that the bird represents a kite: that gravity operates as the string of the kite—

The only motion that is observable is that of tilting of the body. The bird dips forward to throw its weight against the wind— Two forces are operating to produce the curious result we witness. The wind has not only a tendency to raise the bouyant bird, but to carry it off before it. The bird, keeping its wings steadily outstretched dips forward or tilts just enough to give gravity its full force, which you will see is forward and downward against the wind— The result is that the bird by its intelligence floats in the Air as a kite. We know that the string or loop of a kite has to be adjusted very delicately to be buoyant and steady. The bird has the intelligence to adjust itself exactly to oppose its weight to the force of the wind—

The error of all writers on this subject is that they do not reflect that the wind must blow to a certain extent, for the purpose of the bird—

I resided several years on the Florida Reef as Surgeon of our Army Service, and observed the Tachepetes, or Man o War bird, from the top of a Light house.³ From this tower I could with a glass observe very closely, I came to the conclusion herein named at that time, and have felt interested to know how you would regard the matter after my proposition—

It is a singular fact that these “Man o War” birds remain in this position in the air during the night. I have seen them at all hours of the night, and in moonlight or nights quite dark.

I should be much gratified to have a line from you. Meantime I take the liberty to send you one of our Yearly Reports.⁴

The Museum of Natural History is new to New York, but we have a fine collection to start with, hoping to eventually take a respectable place among like Societies—⁵

Very respectfully | Yours. | J. B. Holder M.D. | Asst. American | Museum— | Central Park | New York | U.S.A.