0040.

"Although [Sentinal Island] is likely to have suffered seriously from the effects of the December 2004 tsunami, the survival of the Sentinelese was confirmed when, some days after the event, an Indian government helicopter observed several of them, who shot arrows at the hovering aircraft to repel it."

0039.

Esperanto.

0038.

"As the castrato's body grew, his lack of testosterone meant that his epiphyses (bone-joints) did not harden in the normal manner. Thus the limbs of the castrati often grew unusually long, as did the bones of their ribs. This, combined with intensive training, gave them unrivalled lung-power and breath capacity. Operating through small, child-sized vocal cords, their voices were also extraordinarily flexible, and quite different from the equivalent adult female voice, as well as higher vocal ranges of the uncastrated adult male."

0037.

Canal inclined plane.

0036.

Falkirk Wheel.

0035.

Caisson lock.