“The garuda who live in New Crobuzon are useless for us, by the way. I put up notices in the university, but apparently there’re no garuda students this year. I even tried to argue for the sake of science with a garuda . . . uh . . . community leader . . . and it was a bit of a disaster. Let’s put it that way.” Isaac paused, remembering, then blinked himself back to the discussion. “So instead, let’s look to the birds.

“Now, that leads us to a whole new problem. The little beggars, the humming birds and wrens and whatnot are all interesting and useful in terms of . . . y’know . . . broad background, the physics of flight and what have you, but basically we’re looking at the big boys. Kestrels, hawks, eagles if I’d got hold of any. Because at this stage I’m still thinking analogously. But I don’t want you to think I’m close-minded . . . I’m not studying the mayfly or whatever just out of interest, I’m trying to work out if I can apply it.

“I mean, I’m presuming you’re not fussy, right, Yag? I’m presuming that if I graft onto your back a pair of bat or bluebottle wings, or even a wind-polyp’s flightgland, you’re not going to be fussy. Might not be pretty, but it’s just about getting you into the air, right?”

Yagharek nodded. He was listening fiercely, sifting through the papers on the desk as he did so. He was intent on understanding.

“Right. So it seems reasonable, even given all that, that it’s the big birds we should be looking at. But of course . . .” Isaac rummaged among the papers, grabbed some pictures from the wall, handed sheafs of the relevant diagrams to Yagharek. “Of course, that turns out not to be so. I mean, you can get so far on the aerodynamics of birds, all useful stuff, but it’s actually very misleading to be looking at them. Because the aerodynamics of your body are so fucking different, basically. You ain’t just an eagle with a scrawny human body attached. I’m sure you never thought you were . . . I don’t know how your maths and physics are, but on this sheet here—” Isaac found it and passed it over “—are some diagrams and equations which show you why big birds’ flight ain’t the direction to be looking. Lines of force all wrong. Not strong enough. That sort of thing.

“So, I turn to the other wings in the collection. What if we tacked on dragonfly wings or what have you? Well, first of all there’s the problem of getting hold of insect wings big enough. The only insects big enough already aren’t going to just hand ’em over. And I don’t know about you but I don’t fancy fucking off into the mountains or wherever to ambush an assassin beetle. Get our arses kicked.