Fatio had been raving for some minutes about the Bernoullis – Swiss mathematicians, therefore friends and colleagues of his. 'Sail-makers of a hundred years ago phant'sied that sails worked as literal wind-bags, which is why ships in old pictures all have a big-bellied appearance that is very odd to our modern eyes, as if they need to be taken in . . . now we have learned that sails develop force by virtue of air-currents to either side, shaping, and shaped by, the curve of the canvas . . . but we understand not the particulars . . . the Bernoullis are making this their field of specialization . . . soon we'll be able to use my calculus to loft sails according to rational principles. . . .'