THE SUN. 



revolving in a circle round it at a known distance, and in a known 

 time. 



While, on the one hand, we know the distance and time of the 

 moon's revolution round the earth, we also know the distance and 

 time of the earth's revolution round the sun. We are thus, 

 allowing for the difference of the two distances, in a condition to 

 compare the actual amount of attraction which the earth and the 

 sun respectively exercise upon bodies revolving round them, and 

 we find, accordingly, that the attraction exercised by the sun 

 upon any body is greater than the attraction that would be exer- 

 cised by the earth upon the same body in a like position, in the 

 proportion of three hundred and fifty thousand to one. But as 

 these attractions are, in fact, produced by the respective masses of 

 matter composing the sun and the earth, it follows that the weight 

 of the sun, or what is the same, the mass of matter composing it, 

 is three hundred and fifty thousand times greater than the mass of 

 matter or weight of the earth. 



To make a globe as heavy as the sun, it would then be necessary 

 to agglomerate into one three hundred and fifty thousand globes 

 like the earth. 



9. Having ascertained the weights and bulks of the bodies of the 

 universe, we are in a condition to determine their densities, and 

 thus to obtain some clue to a knowledge of their constituent 

 materials. We have seen that while the bulk of the sun is about 

 one million and four hundred thousand times greater than that of 

 the earth, its weight is greater in the much less proportion of 

 three hundred and fifty thousand to one. Let iis see to what 

 inference this leads in regard to the nature of the matter that 

 composes the sun. If the materials of the sun were similar to 

 those of the earth, its weight would necessarily be greater than 

 that of the earth in the same proportion as its bulk, and in that 

 case, of course, the weight of the sun would be one million and 

 four hundred thousand times that of the earth. But it is not 

 nearly so great as this ; on the contrary, it is much less. Conse- 

 quently, it follows that the constituent materials of the sun are 

 lighter than those of the earth in the proportion of about four to one. 

 The density of the sun is, therefore, about forty per cent, greater 

 than that of water, and, consequently, the weight of the solar orb 

 exceeds the weight of a globe of the same magnitude composed 

 altogether of water, only in that proportion. 



10. Although to minds unaccustomed to the rigour of scientific 

 research, it might appear sufficiently evident, without further 

 demonstration, that the sun is globular in its form, yet the more 

 exact methods pursued in the investigation of physics demand 

 that we should find more conclusive proof of the sphericity of the 



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