THE SOLAR SYSTEM AND ITS NEIGHBORS. 613 



1,000,000,000,000 times its bulk to make a globe one inch in diameter. 

 On such a scale our world would be equaled in minuteness only by the 

 animalcules which the microscope reveals. Even then, on this incon- 

 ceivably reduced scale, the line that would reach our nearest neighbor 

 would need to be something more than three miles long. 



Yet that sun, which in this estimate we have mentally reduced to 

 a point y^q of an inch in diameter, is in reality a body so vast that, 

 were it hollow, and our earth placed at its center, the moon would not 

 only revolve freely around our planet, just as it now does, but on 

 every side the sun would extend more than 200,000 miles beyond the 

 lunar orbit. We have heard so often of the distance from here to the 

 sun, 92 1^ millions of miles, that we begin to think we have some idea 

 of its inconceivable greatness. Yet, so large is the sun that only 107 

 such bodies, laid so as to touch each other, would be needed to form a 

 continuous bridge from the earth to that luminary. In the sky it ap- 

 pears so small that we find it difficult to realize that scarcely more 

 than 100 times its diameter would reach so far. 



However many of us may have sought, by these or by other illus- 

 trations, to form some conception of the vastness of the universe, 

 but few have attempted to grasp the measure of that power which 

 compels the planets to move in elliptical orbits instead of flying off in 

 tangents, as, if left to themselves, they would inevitably do ; and still 

 fewer have thought of the force with which these bodies tend to pull 

 one another out of their courses. Of these influences astronomers have 

 given no illustrations, yet their contemplation will lead to results that 

 will enlarge our views of the universe, and help us to rise at least 

 a little toward a conception of Omnipotence. 



We must work oiit our conclusions ourselves. The data are all at 

 our hand. We need only to know the distances and masses ; the rest 

 is a matter of easy computation. But that our results may not be 

 meaningless from their very greatness, it will be wise to follow the 

 method which we pursue when trying to get an idea of great distances. 

 We take first some unit with which we are familiar for instance, a 

 mile and think how many miles it is to some place familiar to us. 

 Then we extend that measure, or some multiple of it, to another place 

 more remote, and then to one still more distant ; and thus by degrees 

 we become able to grasp distances whose statement in figures had pre- 

 viously conveyed little or no meaning to our minds. So, in measuring 

 a force, we get a better idea of its greatness if we work up to it in a 

 similar manner. 



Of all known substances steel is the most tenacious. If the inter- 

 planetary forces can be represented by steel bars of known size, it will 

 at least help to bring them within the limits of our comprehension. 



Philosophers have found that a steel wire one tenth of an inch in 

 diameter will support nearly half a ton, while a bar one inch square 

 will not be pulled asunder by less than sixty tons. If two inches 



