VAST SIZE OP TAILS. 



that they may be hollow, that is to say, that instead of being 

 cylindrical or conical columns of vaporous matter, they are thin 

 cylindrical or conical tubes of vapour, like the funnel or pipe of a 

 stove. In that case, of course, the bulk or volume of vaporous 

 matter entering into their composition would be much less than we 

 have here computed, but the actual volume included within their 

 limits would still be the same. 



In form the tails are sometimes straight, and sometimes curved 

 like a scymeter, as represented in fig. 2. When the great comet 

 of 1456 appeared it had that form; and in the superstitious spirit 

 of that age, it was regarded as a celestial sign of the success of 

 the Turkish invasion of Europe, from its resemblance to a Turkish 

 sabre. 



The tail is not always single. Comets have appeared with two 

 or more tails. In 1744 a comet appeared with six tails, each of 

 which was curved nearly to the form of a quadrant. 



The magnitude of these enormous appendages is even less 

 amazing than the brief period in which they are sometimes thrown 

 out from the head. The great comet of 1843 had a tail which 

 measured two hundred millions of miles, so that if the head 

 were at the sun, the tail would extend to an hundred millions of 

 miles beyond the earth. Yet this tail was thrown out in less than 

 twenty days. If, as we must suppose, it was wholly composed of 

 matter issuing from the head, with what inconceivable force must 

 not the matter have been ejected which formed the extremity of 

 the tail ! The matter having been driven through two hundred 

 millions of miles in twenty days, must have had a, velocity of ten 

 millions of miles per day. This would be at the rate of above four 

 hundred thousand miles per hour, seven thousand miles per 

 minute, or an hundred and fifteen miles per second. 



This velocity is nearly six times that of the earth in its orbit, 

 and is two hundred and fifty times greater than that of a cannon 

 ball. 



It may be easily imagined that the matter to which such a 

 velocity could be imparted by the reaction of such a body as the 

 comet (itself, according to all probability, consisting of mere 

 vapour), must be infinitely attenuated. 



But there are other proofs how light and rarified must be the 

 matter composing these bodies. 



Since the masses of comets are so infinitely minute, while their 

 volumes are so prodigious, it must follow that the density of the 

 matter composing them is exceedingly small, so small indeed, 

 that they must be, bulk for bulk, immeasurably lighter than air 

 or the most expansive vapour. Other appearances attending 

 them are also consistent with this. Thus it has been found that 



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