SCT. XXXVI. COMET OF 1843. 351 



passed through its perihelion on the 27th of February, 

 when it was lost in the sun's rays ; but it began to be 

 visible about the 3d of March, at which time it was near 

 the star Iota Cetae, and its tail extended toward the 

 Hare. The brightness of the comet and the length of 

 its tail continued to increase till the latter stretched far 

 beyond the constellation of the Hare toward a point 

 above Sirius. Stars were distinctly seen through it, 

 and when near perihelion the comet was so bright that 

 it was seen in clear sunshine in the United States 

 like a white cloud. The motion was retrograde, and 

 on leaving the solar system it retreated so rapidly at 

 once from the sun and earth that it was soon lost sight 

 of for want of light. On the 1st of April it was between 

 the sun and the earth, and only 40 millions of miles from 

 the latter ; and as its tail was at least 60 millions of 

 miles long, and 20 millions of miles broad, we probably 

 passed through it without being aware of it. There is 

 some discrepancy in the different computations of the 

 elements of the orbit, but in the greater number of 

 cases the perihelion distance was found to be less than 

 the semidiameter of the sun, so that the comet must 

 have grazed his surface, if it did not actually impinge 

 obliquely on him. 



The perihelion distance of this comet differs little 

 from that of the great comet of 1668, which came so 

 near the sun. The motion of both was retrograde, and 

 a certain resemblance in the two orbits makes it proba- 

 ble that they are the same body performing a revolution 

 in 175 years. 



Though already so well acquainted with the motions 

 of comets, we know nothing of then* physical constitu- 

 tion. A vast number, especially of telescopic comets, 

 are only like clouds or masses of vapor, often without 

 tails. Such were the comets which appeared in the 

 years 1795, 1797, and 1798. But the head commonly 

 consists of a concentrated mass of light, like a planet, 

 surrounded by a very transparent atmosphere, and the 

 whole, viewed with a telescope, is so diaphanous, that 

 the smallest star may be seen even through the densest 

 part of the nucleus ; in general their solid parts, if they 

 have any, are so minute, that they have no sensible 



