Dr. Herschei/s Observations of a second Comet , 
comet is also much supported by the different appearance of 
the two comets in the observation of the ad of January. In 
order to judge of them properly, we must consider their situa- 
tion with regard to the sun and the earth ; the first comet was 
192 millions of miles from the sun ; the second only 1 64 : the 
first was at the same time 262 millions from the earth: the 
second only 83 ; but notwithstanding the great disadvantage 
of being 28 millions of miles farther from the sun, and about 
179 millions farther from the earth, the first comet had the 
luminous appearance of a brilliant head accompanied by a tail 
45 millions of miles in length ; whereas the second comet, so 
advantageously situated, had only a very faint chevelure about 
its large but faint nucleus, with a still fainter tail, whose length 
has been shown not much to exceed half a million. 
If then the effect of the action of the sun on the comets at 
the time of their perihelion passage is more or less conspicu- 
ous, according to the quantity of unperihelioned nebulous 
matter they contain, we may by observation of cometic phe- 
nomena arrange these celestial bodies into a certain order of 
consolidation, from which, in the end, a considerable insight 
into their nature and destination may be obtained. The three 
last observed comets, for instance, will give us already the 
following results. 
The comet of which this paper contains observations, is of 
such a construction that it was but little more affected by a 
perihelion passage than a planet would have been. This may 
be ascribed to its very advanced state of consolidation, and to 
its having but a small share of phosphoric or nebulous matter 
in its construction. 
That of the year 1807 was more affected, and although 
