35° 



NATURE 



lAiiqitst 9, 1883 



line of descent will be well-nigh perpendicular. We found 

 that, when worked in the manner described above, both 

 trawl and dredge could as a rule without difficulty be 

 made to reach the bottom in the right position. If the 

 dredge or trawl descend much more slowly than the 

 weight, it will fall vertically, with the heavy end foremost. 

 If, on the other hand, its rate of descent be equal to or 

 exceed that of the weights, it will, on reaching the 

 bottom, have a horizontal component in its motion — 

 which is pretty sure to keep it from clogging during the 

 ensuing operation." 



In vol. v. Dr. Mohn renders account of the astronomical 

 observations, as well as the geography and natural history 

 of the expedition, while Capt. Wille describes the mag- 

 netic observations. The vessel was well supplied with 

 suitable instruments for determining latitude and longi- 



tude, and use was made of them whenever favourable 

 opportunities presented themselves. Observations were 

 thus made at nine important points. The various mag- 

 netic elements were determined at eight stations on land 

 and seven at sea. 



The most interesting geographical results of the expe- 

 dition were in connection with Jan Mayen, to which Dr. 

 Mohn devotes considerable space and many fine illustra- 

 tions, several of them coloured. While the expedition 

 was in progress, Dr. Mohn sent us some account of his 

 observations in this island, with illustrations (vol. xviii. 

 p. 222), but of course the subject is more fully treated in 

 the volume before us. Evidences of volcanic action were 

 observed everywhere, and the forms of some of the old 

 craters are very beautiful. As the main object of the 

 expedition was deep-sea research, Dr. Mohn could not 



Fig.: 



give so much time to the observations of the island as he 

 could have wished; nevertheless, by bringing together 

 the observations of the various members of the expedi- 

 tion, and comparing them with the results obtained by 

 Scoresby and other previous observers, Dr. Mohn is able 

 to give a very full and interesting account of this curious 

 island, which we here quote : — 



" Cut off on all sides by extensive ocean tracts from 

 the nearest land, the Island of Jan Mayen occupies an 

 isolated position in the Greenland Sea. Between Norway 

 and Jan Mayen the depth reaches 1760 fathoms, towards 

 Spitzbergen upwards of 2000 fathoms, towards Greenland 

 upwards of 1300 fathoms, and towards Iceland upwards of 

 )ooo fathoms. The direction of the island is from N.E.by 

 E. to SAY. by W. ; it points towards Denmark Strait, and 

 lies parallel to the volcanic line of Mount Hecla. As 

 previously stated, Jan Mayen is built up of volcanic rocks, 

 all of which would appear to belong to the modern group. 



Hence the island is probably a later formation than are 

 the Faeroes and Iceland, where the old volcanic rocks 

 prevail either exclusively or in greater part. Its length 

 slightly exceeds "A geographical mile;. It consists of 

 two large parts or "divisions, a northern and a southern, 

 connected together by a lower and narrower tract. The 

 greatest breadth of the northern part is a little more than 

 2 geographical miles, that of the southern 1 J geographical 

 miles, and the connecting tract (including the lagoon) 

 measures at the narrowest point ii English miles across 

 (0-4 geographical mile). The area of the island is 7'32 

 geographical square miles.'' 



Fig- 3 gives a view of the headland foiming the north- 

 east extremity of North or English Bay, the isolated rock 

 in the distance being the Brielle Tower of the Dutch 

 navigators. 



{To h- continued.) 



