“No problem, captain!” Teafortwo swelled his chest like a bantam. “Big strong lad!”

“Fine. Manage it in one go and I’ll slip you a bit more moolah.”

Teafortwo clutched the list and turned to go with some rude childish yell, when Isaac grabbed the edge of his wing. The wyrman turned, surprised.

“Problem, boss?”

“No, no…” Isaac was staring at the base of his wing, thoughtfully. He gently opened and closed Teafortwo’s massive wing with his hands. Under that vivid red skin, horny and pock-marked and stiff like leather, Isaac could feel the specialized muscles of flight winding through the flesh to the wings. They moved with a magnificent economy. He bent the wing through a full circle, feeling the muscles tug it into a paddling, scooping motion that would shovel air out and under the wyrman. Teafortwo giggled.

“Captain tickle me! Saucy devil!” he screamed.

Isaac reached for some paper, having to stop himself from dragging Teafortwo with him. He was visualizing the wyrman wing represented mathematically, as simple component planes.

“Teafortwo…tell you what. When you get back, I’ll toss you another shekel if I can take a few heliotypes of you and do a couple of experiments. Only half an hour or so. What do you say?”

“Lovely-jubbly, captain!”

Teafortwo hopped onto the window-sill and lurched out into the gloaming. Isaac squinted, studying the rolling motion of the wings, watching those strong muscles unique to the airborne send eighty or more pounds of twisted flesh and bone powering through the sky.

When Teafortwo had disappeared from sight, Isaac sat and made another list, by hand this time, scribbling at speed.

Research, he wrote at the top of the page. Then below it: physics; gravity; forces/planes/vectors; UNIFIED FIELD. And a little below that, he wrote: Flight i) natural ii) thaumaturgical iii) chymico-physical iv) combined v) other.

Finally, underlined and in capitals, he wrote PHYSIOGNOMIES OF FLIGHT.

He sat back, not relaxed but poised to leap. He was humming abstractedly. He was desperately excited.

He fumbled for one of the books he had fished from under his bed, an enormous old volume. He let it topple flat onto the desk, relishing the heavy sound. The cover was embossed in unrealistic fake gold.

A Bestiary Of The Potentially Wise: The Sentient Races Of Bas-Lag.

Isaac stroked the cover of Shacrestialchit’s classic, translated from the Lubbock vodyanoi and updated a hundred years ago by Benkerby Carnadine, human merchant, traveller and scholar of New Crobuzon. Constantly reprinted and imitated, but still unsurpassed. Isaac put his finger on the G of the thumb-index and flipped the pages, until he found the exquisite watercolour sketch of the Cymek bird-people that introduced the essay on the garuda.

As the light ebbed from the room he turned on the gaslamp that sat on his desk. Out in the cool air, away to the east, Teafortwo beat his wings heavily and grasped the sack of books that dangled below him. He could see the bright glimmer of Isaac’s gasjet, and just beyond it, outside the window, the sputtering ivory of the streetlamp. A constant stream of night-insects spiralled it like elyctrons, finding their occasional way through a crack in the glass and immolating themselves in its light with a little combustive burst. Their carbonized remains dusted the bottom of the glass.