The quantity of work whic produces a British unit of heat (or so much heat as elevates the temperature of one pound of pure water, at or near ordinary atmospheric temperatures, by 1 F.) is 772 foot-pounds.
He elevates the present by associating it with the past and future of the world, and sanctifies it by seeing in it the fulfilment of a divine purpose.
It will suffice if such a sail elevates and lowers itself successively.
He states that if the wing only elevates and depresses itself, " the resistance of the air is sufficient to produce all the other movements.
It elevates and propels both when it rises and falls.