Flight, and how Birds get a Rise out of the Wind when Soaring

Extract

This question has been so much discussed within the last few years, and so many are daily observing and studying the flight of every specimen of bird, that it is somewhat astonishing to me I have not yet come across any mention of the method which to my mind accounts for all the wonderful, and, to other theories, apparently impossible results of the ways of an eagle in air. I should be very glad to hear what objections can be raised to my explanation of how soaring is accomplished by any or all of the numerous writers and thinkers whose marvellous mathematical calculations enable them to account for some of the manoeuvres of birds to their own satisfaction. I have not yet seen any description of a theory which claims to account for every movement of all birds, but it must be admitted if any theory falls short of that, it cannot be correct; whilst if it fulfils that condition it cannot be very far wrong.