288 ANNUAL OF SCIENTIFIC DISCOVERY. 



water is only shortened about GO feet. The density is thus hut slightly 

 increased ; but the effect of this enormous pressure upon compressible 

 bodies, as air, wood, etc., is to condense them into a smaller bulk, by -Much 

 they may be rendered hrari'er than icatrr, and will sink of their own weight. 

 A piece of wood cannot float at the bottom of the sea, but a very slight 

 extraneous force will bring it to the surface. 



Now, how is it with the sounding-lead and line? The lead, if allowed to 

 descend alone, will fall with a uniform and rapid velocity to the bottom. 

 This velocity will be attained within a few feet of the surface, and will be 

 due to the opposing forces of gravity and the resistance of the water, which 

 will be balanced, when the uniform velocity is reached. But if a line be 

 attached to the lead, a few hundred feet of the line will offer a resistance 

 to the motion nearly equal to the whole weight of the lead; and as suc- 

 cessive lengths of line are drawn into the water, the resistance is constantly 

 increased; so that at 2000 or 3000 fathoms depth, the weight will be almost 

 entirely suspended in the sea by the resistance of the water along the sides 

 of the line. 



Some idea of the resistance which opposes the motion of a sounding-line 

 may be formed from the fact, that upon 1000 fathoms of a line one-tenth 

 of an inch in diameter, moving with a velocity of three feet per second, the 

 resistance is between twenty-five and thirty pounds; and if the velocity be 

 increased to six feet per second, the resistance upon the line becomes a 

 hundred pounds, nearly. Or, if the length of the line be doubled, with the 

 same velocity, the resistance is doubled; and it is also directly proportional 

 to the diameter of the line. 



These are some of the reasons why an improvement in the mode of 

 measuring the depths of the sea is not only desirable, but necessary, before 

 a certain knowledge of those depths can be obtained. 



THE GEOLOGY OX NEW ZEALAND. 



It will probably be remembered, that a scientific expedition round the 

 world, in the frigate Novara, was organized and despatched, about a year 

 ago, by the Austrian government. Among the scientific officers appointed 

 was Dr. Ferdinand Hochstetter, a geologist of great eminence; and it appears 

 that when the Novara touched and remained for a few days at New Zealand, 

 Dr. Hochstetter was so much struck by the peculiarities and interesting 

 geological features of that country, that he applied for and obtained per- 

 mission to remain six months in that island, in order that he might investi- 

 gate its geology at his leisure, and especially that of the province of Auckland. 

 The general result of Dr. Hochstetter's explorations,* communicated to the 

 New Zealand government, is as follows : 



The first striking characteristic of the geology of Auckland, according to 

 Dr. Hochstetter, is the absence of the primitive, plutonic, and metamorphic 

 formations. The oldest rock that he met with belongs to the primary forma- 

 tion. It is of very variable character, sometimes being more argillaceous, 

 and of a dark color, more or less distinctly stratified, like clay-slate; at other 

 times, the siliceous element preponderates, and from the admixture of oxide 

 of iron, the rock has a red, jasper-like appearance. Xo fossils have hitherto 

 been found in this formation in Xcw Zealand, and therefore it is impossible 

 to state the exact age : it i- possible, however, that these argillaceous, siliceous 

 rocks correspond to the oldest Silurian strata of Europe. The existence and 



