ios Ree ee 
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B. V. Marsh on the Distinguishing Features of Comets. 91 | 
tends to evolve heat, electricity and light, we need scarcely be 
surprised that these are developed on a scale of grandeur far 
surpassing anything with which we are acquainted upon the 
earth 
That small perihelion distance is not the controlling element 
is shown by the total absence of the cometary character in 
the inferior planets, whose orbits lie wholly within the perihe- 
ion of many of the comets. Even the great comet of 1825 
came but little within the orbit of Mars; and.that of 1729 had 
a perihelion distance of 4:04310, being thirteen times that of 
Mercury and almost equal to that of Jupiter. So that we see. 
in Mercury a near approach to the sun without the cometary 
character—and in the comet of 1729 we see the cometary 
character without a near approach to the sun. Excentricity 
: . x . ? 
ing equivalent to an increase in the power of the sun’s rays, 
e 
afford examples of this combination. : } ; 
In order to ascertain whether these views harmonized with 
ich are bce ea 
8d. ? thers, being the only conspicu- 
Donati’s comet, and seven others, being the . ae 
«Catalogue of the Orbits of all Comets hitherto computed,” pub- 
in 1852. _ 
In the followi CBD represents the elliptic orbit of a comet— 
S the sy iia ar bagi major exis—CD a double ordinate through 
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