806 Professor Gautier on the Comet of July 1825. 
orbit of the comet, which has an inclination of 33° 22' to the plane 
of the earth’s orbit, or to that of the ecliptic, of which the figure 
presents the elliptic projection. The sun S occupies the focus 
of each of these orbits. The point E is that in which the earth 
is at the vernal equinox. It is that from which the arcs of 
longitude are counted on the ecliptic, from 0 to 360°, in the di- 
rection from E to o, or in the order of the signs of the Zodiac. 
The right line NN 7 is the line of the nodes of the orbit of the 
comet, or the line of intersection of the plane of its orbit with 
the plane of the ecliptic. The point N is what is named the 
descending node , because it is that through which the comet has 
passed, when it has descended into the portion of its orbit situ- 
ated beneath the ecliptic. The point N' is the ascending node , 
or the point through which the comet passes when it ascends 
above the ecliptic. The position of the line of the nodes is de- 
termined by the angle which it makes on the ecliptic with the 
line SE. I have found the angle ESN', or the longitude of the 
ascending node, to be 215° 36', which gives 35° 36' for the acute 
angle ESN. 
The point P of the orbit of the comet, or the vertex of the 
parabola which it describes, is the point at which it is nearest 
the sun. This is what is called its perihelion ; and the instant 
of its passage through this point, as well as its distance from the 
sun at this instant, are among the number of the most important 
elements of its motion. 
According to my calculation, the comet ought to attain this 
point on the 10th December of the present year, about 11 in 
the morning, or more exactly at 10.456 mean time at Paris, 
reckoned from midnight. The perihelion distance SP ought to be 
once and a quarter the mean distance of the earth from the sun, 
or more accurately 1.23273, this latter distance being taken for 
unity. The mean distance of the earth from the sun, or the 
half of the greater axis of its elliptical orbit, being, as is well 
known, about thirty-four millions and ar-half leagues of twenty- 
five to the degree ; the perihelion distance of the comet from the 
sun should consequently be about forty-two millions and a-half 
of these same leagues. 
There still remains to be determined the direction of the line 
SP, and it has usually been done by finding its longitude upon 
