172 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 174. 



earth is within the body of the sun; and is only the 1068| 

 part of his semidiameter from his centre towards his surface. 

 All globular bodies, whose parts can yield, and which do 

 not turn on their axes, must be perfect spheres, because all 

 parts of their surfaces are equally attracted towards their 

 centres. But all such globes which do turn on their axes 

 will be oblate spheroids ; that is, their surfaces will be 

 higher, or further from the centre, in the equatorial than in 

 the polar regions. For, as the equatorial parts move 

 quickest, they must have the greatest centrifugal force ; and 

 will therefore recede furthest from the axis of motion. Thus 

 if two circular hoops, A B and C D 

 (Fig. 174), made thin and flexible, 

 and crossing one another at right 

 angles, be turned round their axis, E 

 F, by means of this machine, and the 

 axis be loose in the pole or intersec- 

 tion, e, the middle parts A, B, C, D, 

 will swell out, so that the whole will 

 appear of an oval figure, the equa- 

 torial diameter being considerably 

 longer than the polar. That our 

 earth is of this figure is demonstrable 

 from actual measurement of some 

 degrees on its surface, which are found to be longer in the 

 frigid zones than in the torrid ; and the difference is found 

 to be such as proves the earth's equatorial diameter to be 

 thirty-six miles longer than its axis. Price, $7o.OO. 



Whirling Table. A simpler construction of the whirling- 

 table is represented in the next page (Fig. 175), capable of 

 performing most of the preceding experiments in a satisfac- 

 tory manner. Having all the apparatus of the former, and 

 the bearers constructed in a simpler manner, not working so 

 elegantly, but being a less costly arrangement, the frame is 

 made three feet long and one foot wide. Price, $30.00. 



