NATURAL THEOLOGY. 37 



It has been rightly also remarked, that, if the 

 great planets, Jupiter and Saturn, had moved in 

 lower spheres, their influences would have had 



viate beyond a certain distance from the straight course, for the 

 greatest possible deviation would be 3 miles — (the square root of 

 the quotient of 90 divided by the tonnage of the smallest vessel,) 

 — and this supposes neither of the other two to deviate at all ; if 

 they also had their deviations, that would make the smallest ves- 

 sel's deviation so much the less. In hke manner, the second ves- 

 sel never could deviate more than 2, nor the largest more than 1. 

 But these deviations would always be lessened in proportion as 

 the other vessels deviated. If we suppose the three to start from 

 three ports in a straight line from each other, and one port to be 

 64, another 81, and the third 100 miles from the port of destina- 

 tion, and make the condition to be, that the sums of each vessel's 

 tonnage multiplied by the square of its deviation and the products 

 by the sums 8, 9, and 10, respectively, (the square roots of the 

 distances of the three ports of departure,) shall be always equal to 

 the same number, e. g. 90, — the case will resemble more closely 

 the one we are illustrating ; for the proposition of Laplace is, that 

 the sum of the products of the square roots of the transverse axes 

 of the orbits, multiplied by the squares of the eccentricities and by 

 the masses, is always the same, (M6c. C6L liv. ii. c. 7 and 8, es- 

 pecially s. 57. 6 J.) 



The case which we have taken, however, is only by way of il- 

 lustration, and does not resemble the one in question as to parti- 

 culars. Moreover, in order that all the three vessels may be able 

 to obey the rule during each part of their course, we must suppose 

 one of them to start from a point on one side of the port, and the 

 same vessel, or another of them, to make a port different from the 

 port of destination. This difficulty would be removed by suppo- 

 sing the condition to be, that the sums of the products should 

 never exceed a certain amount. 



In the case put it is clear that, practically speaking, no combi- 

 nation among the navigators could make the vessels perform their 

 voyage according to the condition, unless by two of the vessels 

 going in the straight line, and the third in a line parallel to it. 

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