Lectures on astronomical theories . -^ni. Butthis, again, is the average difference ; and evidently at ornear the earths quadrature, when the recession or ap-proach is more rapid, the difference would be greater. Ifwe take the number of revolutions at about 190, theaverage difference in a single revolution, on the oppositesides of the orbit respectively, would be one-third of aminute, and if at or near quadrature, the difference would,perhaps, exceed halfa minute.* Supposing, however, thedifference on a single revolution of the satellite to be con-siderably less than this, it would still be a
Lectures on astronomical theories . -^ni. Butthis, again, is the average difference ; and evidently at ornear the earths quadrature, when the recession or ap-proach is more rapid, the difference would be greater. Ifwe take the number of revolutions at about 190, theaverage difference in a single revolution, on the oppositesides of the orbit respectively, would be one-third of aminute, and if at or near quadrature, the difference would,perhaps, exceed halfa minute.* Supposing, however, thedifference on a single revolution of the satellite to be con-siderably less than this, it would still be a quantity oftime which the practical astronomer can readily , then, is one of the distinct requisitions of Roemersassumption which can be directly submitted to the deci-sion of experience. * If the earth receded (and approached) uniformly for equal incre-ments of time, each revolution of the satellite during the recession (orapproach), according to the assumption, would lose (or gain) an equalamount of time. FUf*. / Fig V. TELOCITY-OF-LIGHT THEORY. 43 Let US now consider what effects would be necessarilyconsequent upon some very small quantity of time beingoccupied by light, in its communication from the sun toJupiter, and from Jupiter to the earth. The quantityof time attributed by the theory (of the velocity of light)to a certain (definite) quantity of motion, seems to us lessthan reason authorizes the mind to accept as a (reasonable)possibility; or, in other words, the velocity attributedto light, by that theory, seems to us greater than is scien-tifically conceivable, keeping in mind that, by the theory,this velocity represents the actual progressive motion ofa variety or form of matter (?. e., of a material substance).To simphfy the consideration of the subject, however,we will assume, for the moment, the possibility of suchvelocity, and suppose it to be S minutes for a distance of100 million miles. We w411 take Jupiters distance roughlyat 500 million miles, and
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