480 Proceedings of Learned Societies. 



EOTAL INSTITUTION". 



On Force. — Dr. Tyndall's Lecture on the Correlation of Mecha- 

 nical Force and Heat, delivered before the members of the Royal 

 Institution, offers so many remarkable facts, that we are desirous to 

 reproduce them in a condensed form. A substance suspended at a 

 height of sixteen feet above the earth's surface, and allowed to fall, 

 reaches the surface in one second of time, its velocity, which has 

 been regularly accelerated, being then at the rate of thirty-two feet 

 per second. If the movement of this falling body is arrested, the 

 force is not lost, but converted into heat. Thus the force of a body 

 falling sixteen feet is sufficient, if suddenly arrested, to raise its 

 temperature three-fifths of a degree Fahrenheit. The work done, 

 or the mechanical force exerted by any moving object, augments 

 with the square of the velocity ; thus, doubling the weight of a 

 cannon-ball doubles its power; but doubling its velocity, though 

 the original weight is retained, quadruples its effect. Hence the 

 efforts of artillerists to augment the velocity of their projectiles. A 

 rifle bullet has at least forty times the velocity of a body falling for 

 one second : hence, when suddenly arrested, as by an iron target, 

 the heat generated, provided it could be concentrated in the bullet, 

 would raise its temperature to about 960°, sufficient to melt the lead. 



The conversion of muscular force into heat is strikingly shown 

 in the concussion of flint and steel, as in the old method of obtaining a 

 light. Energetic chemical union is always attended with the evolution 

 of heat, which may be regarded as being produced by the falling to- 

 gether of atoms at a high velocity. The heat so evolved can be made 

 to reproduce the exact amount of force that was arrested in its 

 production. Thus, the union of a pound of coal with about two 

 pounds of oxygen evolves an amount of heat capable, if properly 

 applied, of raising a hundred pounds weight to a height of twenty 

 miles. The coal raised every year in England amounts to 84,000,000 

 tons, which, were they all applied to the production of force, would 

 be equal to 108,000,000 horses working constantly ; or a pound of 

 coal may be regarded as equal to the force of three hundred horses 

 working for one minute. 



The fact that force may be converted into heat has given rise to 

 a theory which attributes the light and heat evolved from the sun 

 to the falling of meteoric bodies on to its surface. Of the amount 

 of heat produced by this luminary, some idea may be gained from 

 the fact that the earth receives only 1-2, 300,000,000th part. More- 

 over, it is calculated that the heat given out by the sun every 

 minute is sufficient to boil 12,000,000 cubic miles of ice-cold water. 

 This vast amount of heat is supposed by Dr. Mayer of Hcilbron to 

 be due to the falling into the sun of meteoa*ites. The objection to 

 the theory that these bodies are too few in number is met by the 

 fact, that at one observatory alone as many as 240,000 have been 

 observed in nine hours. 



Meteoric bodies attracted by the sun would necessarily move 

 with a high and rapidly-accelerating velocity, and it is calculated 



