100 ON COMETS. 



going to say will be already well known to a portion of 

 them, but will be quite new to many, and I will try to 

 put it in such a way as shall not only be clearly intel- 

 ligible, but shall stick by them, and become part and parcel 

 of their minds and thoughts henceforward and I am 

 mistaken if many of this class of hearers (provided they 

 will give me the attention the thing requires) do not rise 

 from the perusal of this brief statement with much larger 

 and higher conceptions of the magnificent system we 

 belong to than they commenced it with. 



(8.) The sun, as we all know, or may have heard, stands 

 immovable, or nearly immovable, in the centre of our 

 system, and all the planets, including the earth, circulate 

 or revolve round it, each in its own time and at its own 

 proper distance. These distances, for each planet, stand 

 to each other in relations of proportional magnitude, 

 which have become, by a long course of astronomical 

 observation and calculations, known to us with extreme 

 exactness, so that if the exact distance of any one of the 

 planets from the sun, or the exact interval between any 

 two of their orbits, can anyhow be ascertained in miles, 

 yards, or feet, the dimensions of all the rest in similar 

 units of measure may thence be derived. Supposing, 

 for instance, we knew exactly the interval between the 

 orbits of the earth and Mars, then if we would know the 

 respective distances of the several planets in their order 

 from the sun, it would only be necessary to multiply 

 that interval, in the case of Mercury, by the decimal 

 fraction 07392; in that of Venus by i - 38i2; of the 

 Earth by 1-9095; of Mars by 2-9095; of Jupiter by 



