22 THE POPULAR SCIENCE MONTHLY. 



the four sides of the pit, and a kilometre or so cut off the lower pointed 

 end to allow space for its descent. The mass of this weight is 326 X 

 10 6 tons. Its heaviness, three quarters of the heaviness of an equal 

 mass at the sun's surface, is 244 XlO 6 tons solar surface-heaviness. 

 Now a horse-power is 270 metre-tons, terrestrial surface heaviness, per 

 hour ; or ten metre-tons, solar surface-heaviness, per hour. To do 

 78,000 horse-power, or 780,000 metre-tons, solar surface-heaviness, per 

 hour, our weight must therefore descend at the rate of one metre in 

 313 hours, or about twenty-eight metres per year. 



To advance another step, still through impracticable mechanism, 

 toward the practical method by which the sun's heat is produced, let 

 the thread of the screw be of uniformly decreasing steepness from the 

 surface downward, so that the velocity of the weight, as it is allowed 

 to descend by the turning of the screw, shall be in simple proportion 

 to distance from the sun's center. This will involve a uniform con- 

 densation of the material of the weight ; but a condensation so ex- 

 ceedingly small in the course even of tens of thousands of years, that, 

 whatever be the supposed character, metal or stone, of the weight, 

 the elastic reaction against the condensation will be utterly imper- 

 ceptible in comparison with the gravitational forces with which we 

 are concerned. The work done per metre of descent of the top end of 

 the weight will be just four fifths of what it was when the thread of 

 the screw was uniform. Thus, to do the 78,000 horse-power of work, 

 the top end of the weight must descend at the rate of thirty-five me- 

 tres per year : or seventy kilometres, which is one one hundredth per 

 cent (tttoott) f the sun's radius, per two thousand years. 



Now let the whole surface of our cool solid sun be divided into 

 squares, for example, as nearly as may be, of one square metre area 

 each, and let the whole mass of the sun be divided into long, inverted 

 pyramids or pointed rods, each 700,000 kilometres long, with their 

 points meeting at the center. Let each be mounted on a screw, as 

 already described for the long tapering weight which we first con- 

 sidered ; and let the paddle at the top end of each screw-shaft revolve 

 in a fluid, not now confined to a vat, but covering the whole surface 

 of the sun to a depth of a few metres or kilometres. Arrange the vis- 

 cosity of the fluid and the size of each paddle so as to let the paddle 

 turn just so fast as to allow the top end of each pointed rod to descend 

 at the rate of thirty-five metres per year. The whole fluid will, by 

 the work which the paddles do in it, be made incandescent, and it will 

 give out heat and light to just about the same amount as is actually 

 done by the sun. If the fluid be a few thousand kilometres deep over 

 the paddles, it would be impossible, by any of the appliances of solar 

 physics, to see the difference between our model mechanical sun and 

 the true sun. 



Now, to do away with the last vestige of impracticable mechanism, 

 in which the heavinesses of all parts of each long rod are supported 



