622 PHILOSOPHICAL TRANSACTIONS. [aNNO 1723. 



The path of the comet passed above the back of the Ursa Minor, near the 

 pole star, through the legs and knees of Cepheus, Cassiopeia, and Andromeda ; 

 its descending node was in 21-1-° of Aries, with some mutation; the angle of 

 the cometic orbit and ecliptic was about 69-^°, with some variation too; the 

 path of the comet was almost 2° from the pole of the world, and intersected 

 the equator in 20^-° from the equinoctial point; its perigaeum was in 6° 6' of 

 Virgo, with 62° 7' N. lat. The comet was in its perigaeum on the 18th of 

 January 3^ 9*" in the morning; its diurnal motion in its orbit was 22° 8' in the 

 perigaeum, viz. 12 hours before and 12 hours after the perigaeum, but on the 

 last days of its appearing 32'. Supposing tlie earth at rest, and the comet 

 moving in a right line, the motion of the comet was 39 1 such parts, as the 

 least distance of the comet from the earth is 1000. M. Kirch could determine 

 nothing with certainty about the parallax of the comet, only that it was a great 

 deal higher than the moon ; and he conjectures, with some probability, that it 

 moved within the orbits of the planets; nay, that in its perigaeum it was much 

 nearer to us than the sphere of Mars. For, suppose the semidiameter of the 

 earth's orbit be 10,000 parts, the diurnal motion of Mars will be 139 or 140 

 such parts. If we suppose the comet to have been in the orbit of Mars, with 

 62° 7' lat. and 22° S' diurnal motion, its velocity would be 2847 parts, suppos- 

 ing at the same time it was in opposition to the sun; but since the diti^erence 

 of long, of the sun and comet in its perigaeum was only 141° 40', the diurnal 

 motion of the comet becomes 3200 parts, and the proportion of the motion of 

 the comet to the motion of Mars as 23 to 1 ; wherefore he collects, that the 

 comet moved within the sphere of Mars. But should any one suppose the 

 comet to have moved within the orbit of Saturn, it should then have a velocity, 

 which would be to the velocity of Saturn, as 600 to 1 , and that in one day it 

 would run over a greater space than the earth does in half a year; not to men- 

 tion the diameter of the comet, which should be no less than 3 diameters of 

 the sun. 



M. Kirch, comparing this comet with others, found that observed by Regio- 

 montanus, in January and February 1472, or 1475, moved in a tract not very 

 different from it; for it passed through Ursa Minor, the thighs of Cepheus, 

 the breast or neck of Cassiopeia, and the girdle of Andromeda; and its greatest 

 velocity in a day was 40°. Another comet was observed in 1556, whose nodes 

 Camerarius placed in 11° of Libra and Aries, and which passed near the feet 

 of Ursa Minor, through Cepheus, above Cassiopeia, and through the upper 

 parts of Andromeda, with a very swift motion in its perigaeum. And if Regio- 

 montanus observed a comet in 1475, which astronomers very much doubt, 

 there would be a surprising coincidence between these three comets; for, the 



