MEASURE OF THE 6UN ? 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 vis 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, 



