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Darwin Correspondence Project

From Robert Shaw   10 December [1876]1

Glassaugh, Portsoy, | Banffshire. N.B.

10 Decr

Dear Sir

It did not strike me in writing to you that there is another buoyant factor in the power of continuous soaring. The whole inner downy plumage of birds must be a magazine of rarefied air encased by the harder and stiffer outward covering. This in aquatic birds we know to be impervious to water. From the serrated (I think that is the term used) structure of the web or plume of feathers they must overlying each other as they do, be almost impervious to the outer air and thus while retentively enclosing a consider body of heated air add to the buoyancy of a soaring bird; perhaps more than all the other sustaining aids.2

I think this assumption is scientifically reasonable enough. To me the power of soaring is no longer a thing which should perplex us any more than our power of walking. I am accidentally without your address and am therefore obliged to write to you in a round about way.

Yours faithfully | R Shaw


The year is established by the relationship between this letter and the letter from Robert Shaw, 28 November 1876.
Shaw had hypothesised about the mechanics of soaring in birds in a letter to Land and Water, 8 January 1876, p. 8, a clipping of which he enclosed in his letter to CD of 28 November 1876.


Adds a point to his previous letter regarding the buoyancy of birds and their soaring capacity.

Letter details

Letter no.
Robert James (Robert) Shaw
Charles Robert Darwin
Sent from
Source of text
DAR 177: 154
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 10707,” accessed on 4 October 2023,

Also published in The Correspondence of Charles Darwin, vol. 24