COLCHICUM, or Meadow Saffron, is a plant with a solid rootstock or cormus, found wild in various parts of Europe and in Great Britain, forming a gay carpet in the autumn in the fields, where its lively purple crocus like flowers spring up. Its corms and its seeds abound in an acrid, stimulating, de leterious principle, which has been carefully examined by modern chemists, and forms an important plant in the Materia Medica, large quantities of both corms and seeds being an nually consumed in the manufacture of Eau .3Ikdicinale, and other medicinal preparations. COLLISION, When a body in motion strikes another, whether at rest or in move ment, the particles of the first body, at the place of contact, have their forward motions retarded,in consequence of which the particles immediately behind approach closer to those in front than they were before the impact, and thus a condensation takes place. This con densation gives rise to an exertion of the force of elasticity, which acts against the succeeding particles, retarding the motions of these last and giving rise to a new condensation and a new exertion of elasticity against the next succeeding particles ; and so on. The like actions must be understood to take place in the body struck ; and these actions continue in both bodies till the bodies have attained the state of greatest compression, when, for a mo ment, both may be conceived to move with a common velocity. After this, the force of
elasticity overcoming the force of compression, the particles of both bodies gradually return to a permanent state, which, if the elasticity were perfect, would be the same as that in which they were before the impact, the force of restitution thus causing the bodies to sepa rate as if repelled from each other. A certain interval of time elapses between the instants of first contact and separation, but this is so short as to be scarcely sensible.
If the bodies have different degrees of hard ness, an indentation may take place in that which is the least hard, the other penetrating to a certain distance in it. When the bodies are soft, like halls of wet clay, the change of figure produced by collision is manifest. When the hardness is very great, a vast resistance arising from friction will be overcome by the percussion arising from the descent of a com paratively small rammer. It has been ob served that a sledge-hammer, in driving hard pegs, produces an effect equivalent to the pressure of 70 tons. It is from this circum stance that collision or percussion is a very valuable mode of applying force, in many of the manufacturing arts connected with machi nery.