OTHER ELLIPTIC COMETS. 



while its angular motion in aphelion is little more than half that 

 of Neptune. 



The corresponding variations of solar light and heat, and of the 

 apparent magnitude and motion of the sun as seen from the comet, 

 may be easily inferred. 



IV. ELLIPTIC COMETS WHOSE MEAN DISTANCES EXCEED THE 

 LIMITS OF THE SOLAK SYSTEM. 



72. Although the periodicity of this class of comets has not yet 

 in any instance been certainly established by observations made 

 upon their successive returns to perihelion, the observations made 

 upon them during a single perihelion passage indicate an arc of 

 their orbit, which exhibits the elliptic form so unequivocally, as 

 to supply computers and mathematicians with the data necessary 

 to obtain, with more or less approximation, the value of the eccen- 

 tricity, which, combined with the perihelion distance, gives the 

 form and magnitude of the comet's orbit. 



By calculations conducted in this manner, and applied to the 

 observations made on various comets which have appeared since 

 the latter part of the seventeenth century, the elliptic orbits of 

 twenty-one of these bodies have been computed, and are given in 

 the order of the dates of their perihelion passages in a table which 

 will be found in my " Hand-Book of Astronomy." 



Of this group the least eccentric is No. 15, which passed its 

 perihelion in 1840. This comet was discovered at Berlin by M. 

 Bremiker, and its orbit was calculated by Gotze, and proved to 

 be an ellipse, having the elements given in the table, subject to 

 no greater uncertainty than ith of the value assigned to the mean 

 distance. The eccentricity, and consequently the form of the 

 orbit, is similar to that of Halley, but the major axis is 2| times, 

 and the period nearly five times greater. Its perihelion distance 

 is equal to that of Mars, and its aphelion distance more than three 

 times that of Neptune. 



No. 6, which passed its perihelion in 1793, has an orbit, accord- 

 ing to the calculations of D' Arrest, nearly similar both in form and 

 magnitude, as will be seen by comparing the numbers given in 

 the table. More uncertainty, however, attends the estimation of 

 these elements. 



The comets which approached nearest to the sun were the great 

 comets of 1680 and 1843, Nos. 1 and 16 in the table, both memor- 

 able for their extraordinary magnitude and splendour. 



The elements of that of 1680, given in the table, are those 



185 



