384 Clusters and Nebulae. 



At some distance S. of Huygens lies Marco Polo, an oval 

 depression in the high ground, without a ring, visible chiefly 

 in the wane, and remarkable as the centre of convergence of a 

 number of narrow valleys. N. and N.W. of it the hill-grouping 

 is beautiful. 



The eastern part of the Apennines is much of the same 

 character : a plateau covered with slightly connected ridges and 

 chains of hills, running chiefly parallel in a S. direction. Its 

 edge towards the M. Imbrium still nowhere descends below 

 6400 feet ; a lower chain runs parallel to it through the plain 

 at eighteen miles distance. Towards its S.E. extremity rises 

 an almost separate mass, bearing numerous peaks, some of 

 which attain 11,500 feet, and at this place it turns back at 

 right angles to its previous direction, to form the N.W. shore 

 of the Sinus JEstuum (H). Beyond the angle, however, and 

 beyond some narrow gorges uniting the two plains, the original 

 range reappears in a small, nearly rectangular plateau, whose 

 summit, Wolf, attains, according to Schr., 11,700 feet (B. and 

 M., 11,000 feet). Then a narrow and interrupted chain of 

 inferior eminences stretches on in advance like a row of 

 gigantic stepping-stones, till it forms a singular connection 

 with the wall of the great crater Eratosthenes (29), and so 

 brings to an end one of the most magnificent as well as 

 extensive mountain masses of our satellite.* 



CLUSTERS AND NEBUL2E. 



The time of year has now become unfavourable for the 

 examination of the fainter objects in the heavens, and those 

 which we are going to mention ought to have been pointed out 

 earlier. However, they may still be found in clear and moon- 

 less nights, and the knowledge of their position will prepare 

 us for another examination under more advantageous circum- 

 stances. The first is in a space so barren to the eye that, 

 unless we possess the convenience of divided circles (when we 

 should find it in R.A. xiiih. 36m. D.N". 29° 1'), we must 

 pick it up by sweeping. It lies about one-third of the distance 

 from Arcturus to Cor Caroli, and not much out of the line ; 

 and if this part of the sky is carefully traversed, our finder 

 will soon come across a misty speck, which in the -telescope 

 will fully reward our pains. It is 



41. The great cluster in Canes Venatici. — Gen. Cat. 

 3636. — M. 3. Smyth describes this as a brilliant and beautiful 

 congregation of not less than 1000 small stars, 5' or 

 6' in diameter, blazing splendidly^ towards the centre, and 

 compressed on the sf side, as having no outliers there; 



* B. and M. observe a considerable and unusual difference between their map 

 and Lohrmann's "Section" throughout this intricate region. 



