MEASURE OF THE SUN's HEAT. 267 



has a tendency to produce equal motion of the two rubbing 

 bodies ; and when this is attained, the generation of heat 

 ceases. If now the sun be the one moving body, where is 

 the other ? and if the second body exist, what power prevents 

 it from assuming the same rotary motion as the sun ? 



But could even these difficulties be disregarded, a weight- 

 ier and more formidable obstacle opposes this hypothesis. 

 The known volume and mass of the sun allow us to calculate 

 the v is viva which he possesses in consequence of his rotation. 

 Assuming his density to be uniform throughout his mass, and 

 his period of rotation twenty-five days, it is equal to 182,300 

 quintillions of kilogrammetres (Km). But for one unit of 

 heat generated, 367 Km are consumed; consequently the 

 whole rotation-effect of the sun could only cover the expendi- 

 ture of heat for the space of 183 years. 



The space of our solar system is filled with a great num- 

 ber of ponderable objects, which have a tendency to move 

 towards the centre of gravity of the sun ; and in so doing, 

 their rate of motion is more and more accelerated. 



A mass, without motion, placed within the sphere of the 

 sun's attraction, will obey this attraction, and, if there be no 

 disturbing influences, will fall in a straight line into the sun. 

 In reality, however, such a rectilinear path can scarcely occur, 

 as may be shown by experiment. 



Let a weight be suspended by a string so that it can only 

 touch the floor in one point. Lift the weight up to a certain 

 height, and at the same time stretch the string out to its full 

 length ; if the weight be now allowed to fall, it will be ob- 

 served, almost in every case, not to reach at once the point on 

 the floor towards which it tends to move, but to move round 

 this point for some time in a curved line. 



The reason of this phenomenon is that the slightest devia- 

 tion of the weight from its shortest route towards the point 

 on the floor, caused by some disturbing influence such as the 

 resistance of the air against a not perfectly uniform surface, 



