ON THE SUN'S HEAT. 377 



mechanism, take a long vertical shaft, with the 

 paddle mounted on the top of it so as to 

 turn horizontally. Let the weight be a nut 

 working on a screw-thread on the vertical 

 shaft, with guides to prevent the nut from 

 turning the screw and the guides being all 

 absolutely frictionless. Let the pit be a metre 

 square at its upper end, and let it be excav- 

 ated quite down to the sun's centre, every- 

 where of square horizontal section, and taper- 

 ing uniformly to a point in the centre. Let 

 the weight be simply the excavated matter of 

 the sun's mass, with merely a little clearance 

 space between it and the four sides of the pit, 

 and with a kilometre or so cut off the lower 

 pointed end to allow space for its descent. The 

 mass of this weight is 326 million tons. Its 

 heaviness, three-quarters of the heaviness of an 

 equal mass at the sun's surface, is 244 million 

 tons solar surface-heaviness. Now a horse-power 

 is, per hour, 270 metre-tons, terrestrial surface- 

 heaviness ; or 10 metre-tons, solar surface-heavi- 

 ness, because a ton of matter is twenty-seven 



