THE PLURALITY OF WORLDS. 



earth, then, the weight of bodies on the planet, on that account alone, would be 

 sixteen times greater. The weight, then, on the one score, would be sixteen 

 times greater, and on the other, four times less ; the result being that the actual 

 weight under such circumstances, would be four times greater than upon the 

 earth. Such are the principles by which may be calculated the weights of 

 bodies upon the surfaces of the different planets. It has been found that the 

 weights of bodies on the surfaces of Mercury, Venus, and Saturn, are nearly 

 the same as upon the earth ; that upon Mercury they are one half less, and on 

 Jupiter three times more. Thus it is apparent that there are no very extreme 

 deviations in weight, comparing the surface of one planet with another, and 

 hence we are led to infer the probability of an organization not very different 

 upon the several planets. 



We have already explained by how easy means the great variety of light 

 and warmth conveyed to the different planets by the sun may be practically 

 equalized, by the adaptation of the organization of the eye, and the regulation 

 of the density of the atmosphere. Since, however, this difference in the physi- 

 cal condition of the planets excites usually much attention, it may be well here, 

 before closing this discourse, to enlarge somewhat further on this point. 



The principles of optics prove that the sun's light will be less upon the 

 planet Mars than upon the earth, in the proportion of one to two. Jupiter will 

 receive about twenty-five times, and Saturn about one hundred times less 

 warmth than the earth does, while the diminution in the case of the most re- 

 mote planet, Herschel, will be nearly four hundred fold ; on the other hand, 

 Venus and Mercury, being nearer to the sun than the earth, the one will re- 

 ceive twice, and the other seven times, as much light and warmth as the earth 

 does. The apparent magnitude of the sun to these planets will be in the same 

 proportion. To Jupiter it will have an apparent diameter five times less than 

 to the earth. To Saturn the diameter will be ten times less, and to the planet 

 Herschel nearly twenty times less. 



The apparent magnitude of the sun as we behold it is measured by an angle 

 of about thirty minutes ; consequently, to the inhabitants of the planet Herschel 

 it will appear under an angle less than two minutes, or about three times the 

 size of Jupiter when that planet appears the largest and brightest. We should, 

 however, form a very erroneous estimate of the actual light of the sun under 

 these circumstanes by these comparisons. It shines by its own light, whereas 

 the objects with which it is attempted to be compared shine with reflected 

 light. The full moon has the same apparent magnitude as the sun, the differ- 

 ence being that the one shines with direct, and the other with reflected light ; 

 how much is lost in splendor on this score may be judged, when we state that 

 the light of the full moon is three hundred thousand times less than that of the 

 sun ; we may also form some guess at the effect of the sun's light, even at the 

 most remote planet, Herschel, when it is stated that it gives a light equal nearly 

 to that of a thousand full moons. 



If we could actually behold the da% of Saturn and Herschel on the one 

 lined, and of Mercury and Venus on the other, we should be surprised how 

 disproportionate to their numerical representation their apparent splendor would 

 be. The eye is a bad photometer. In a solar eclipse, in which half the sun's 

 disk is covered, we are scarcely sensible of diminished light ; and even when 

 the eclipse is nearly total when only a thin crescent of the sun remains un- 

 covered there is still the broad light of day, though very sensibly diminished 

 in splendor. A thick covering of clouds upon the firmament produces an im- 

 mense numerical diminution of the light of day, yet we suffer no inconveni- 

 ence in being exposed to all the varying degrees of splendor between that and 

 ihe unclouded radiance of a summer's sun. 



