taken at the Lowell Observatory. 493 



As we have seen that he more nearly approaches the 

 central concentrated than the homogeneous state we may 

 take 2*54 as the value. His centrifugal force, so called, at 

 his equator is 



a! T 2 1 



— 7iT7o -777- , or *23 times the Earth's attraction, 

 a 1 /J 2b9 



whence we finally get 



2*31 for the force of gravity at his equator compared 

 with that at the Earth's. 



If Jupiter were cold this would cause a density greatly 

 exceeding the Earth's, while the facts are the other way, 

 Jupiter's mean density heing to the Earth's as 1*32 to 5'527. 

 It is evident, therefore, that he must be expanded by 

 heat. 



Furthermore, the gradation in density from core to cuticle 

 must be gradual. There can be no sudden change from a 

 dense kernel of Jupiter to a vast gaseous husk. For the 

 great pressure in such a case would act to thin the air 

 envelope relatively more than in the case on Earth. Nor 

 would any permissible increase in the relative amount of 

 air held by the planet come within the figures needed. 

 For if the density of the nucleus were only that of the 

 Earth, a modest estimate, the volume of the air outside it 

 would be about 9 times its own, an amount of air with 

 which we have no warrant for crediting it. 



2. The next point is the position of the several belts. 

 The measures of the images on the plates of April 14 give 

 for their apparent places, taking the polar radius as the 

 radius of the sphere of comparison, which, since the tilt was 

 only 1°*3, may be taken as the apparent minor axis of the 

 ellipse : — 



Antarctic belt -37°-2 



South Temperate belt -27°'6 



South edge of S. Tropical belt . . . . -19°\ r > 



dark line in ,, „ . . . . — 15°'9 



North edge of South Tropical belt ... — 6°' 8 



North Tropic belt -f 9°*4 



North stripe of S. Tropical belt . . . +17°'8 



North Temperate belt -f35 o, 



At the time the photographs were taken. April 14, the 

 latitude of the planet's equator with regard to the Earth was 

 - 1°3. 



