METHODS OF EXCITING AND COLLECTING HEAT.

65

SECT. II.

METHODS

OF

EXCITING AND COLLECTING HEAT.

"F the different methods of exciting heat, the following aretile most usual:

1. PRODUCTION OF HEAT

BY

PERCUSSION OR COLLISION.

This method of producing heat is the simplest, and there-fore it is generally made use of in the common purposes of lifefor obtaining fire.

When a piece of hardened steel is struck with a flint, someparticles of the metal are scraped away from the mass, and soviolent is the heat which follows the stroke, that it melts and vi-trifies them. If the fragments of steel are caught upon paperand viewed with a microscope, most of them will be found per-fect spherules, and very highly polished. Their sphericity de-monstrates that they have been in a fluid state, and the polishupon their surface shows them to be vitrified.

No heat however has been observed to follow the percussionof liquids, nor of the softer kind of bodies which yield to a slightimpulse.

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