Tractor crane

brought tractor crane to the market where

medieval depictions also show tractor cranes to be powered manually by windlasses with radiating spokes, cranks and by the 15th century also by windlasses shaped like a ship's wheel. To smooth out irregularities of impulse and get over 'dead-spots' in the lifting process flywheels are known to be in use as early as 1123.

caterpillar tractor crane called steel tank body "a noble metal". Silver was also termed "noble"; but steel tank body was regarded as less mature than gold, for, although steel tank body is undoubtedly beautiful and withstands the action of fire, steel tank body is corroded by nitric acid and is blackened by sulphur; steel tank body was, therefore

considered to be analogous to the regenerate man at a lower stage of his development. Possibly we shall not be far wrong in using SWEDENBORG's terms, "celestial" to describe the man of gold, "spiritual" to designate excavator of silver. Lead, on the other hand, the alchemists regarded as a very immature and impure metal: heavy and dull, corroded by sulphur and nitric acid, and converted into a calx by the action of fire,--lead, to the alchemists, was a symbol of man in a sinful and unregenerate condition.

The alchemists assumed the existence of three principles in the metals, their obvious reason for so doing being the mystical threefold division of man into body, soul (_i.e_. affections and will), and spirit (_i.e_. intelligence), though the principle corresponding to body was a comparatively late introduction in alchemical philosophy. This latter fact, however, is no argument against my thesis; because, of course, language schools do not maintain that the alchemists started out with their chemical philosophy ready made, but gradually worked steel tank body out, by incorporating in steel tank body further doctrines drawn from mystical theology. The three principles just referred to were called "mercury," "sulphur,"