November 8, 1900] 



NATURE 



37 



In the Bulletin of the Cracow Academy, experiments are 

 described by Constantin Zakrzewski on the electromotive force 

 produced by the motion of a liquid through a silvered glass tube. 

 The tube in question was a capillary tube connecting two large 

 glass vessels half filled with water, and the electrodes terminated 

 in the water at a short distance from the end of the tube. The 

 flow of water was brought about by introducing compressed air into 

 one of the vases. A current of water was always found to be ac- 

 companied by an electric current the direction of which depended 

 on the water current, and the electromotive force was found (i) 

 to vary as the difference of pressure at the ends of the tube ; (ii) 

 to depend on the distance of the electrodes from the ends of the 

 tube, the effect of increasing this distance in the case of the elec- 

 trode opposite the entering stream being to decrease the electro- 

 motive force. It is suggested that this result confirms the 

 hypothesis of Quincke and Helmholtz, according to which the 

 electromotive force has its origin in a kind of tearing of the 

 layer of contact electricity between the silver and the 

 water. The electromotive force depends on the thickness of 

 the silvering, and decreases when the thickness increases. In 

 the case of a solution of nitrate of silver, the electromotive force 

 vanishes and changes sign when the concentration is equal to 

 1/3000 of the normal. 



About three years ago. Dr. Folgheraiter published a descrip- 

 tion of observations of the " distinct " points and zones in the 

 magnetisation of rocks, and showed that these singularities, of 

 which he had observed a number in the Campagna, were due 

 to lightning discharges. In a recent issue (No. lo) of the 

 Frammenti concernanti la geq/isica dei Pressi di Roma, the 

 same author gives an account of certain measurements made 

 with the object of determining (i) to what distance the mag- 

 netism produced by lightning produces any sensible action ; (2) 

 the direction of the magnetising lightning-discharge. The re- 

 sults already arrived at show that in certain singular zones {zone 

 distinte) the direction of discharge is determinable, and the 

 magnetic properties and distribution of magnetism resemble 

 those of an ordinary magnet ; while in the case of other zones 

 it has been impossible, as yet, to ascertain either the direction 

 of the magnetising discharge or the position of one of the two 

 magnetic poles. 



In a recent number of Terrestrial Magnetism and Atmo- 

 spheric Electricity {\., 2), Mr. William Sutherland puts forward a 

 possible cause of the earth's magnetism and a theory of its 

 variations. The cause suggested is the rotation of the electro- 

 static field within the earth, as Rowland's experiments have 

 proved that a moving charge of electricity produces a magnetic 

 field analogous to that of a current. If the earth carries round 

 an electrostatic field in its rotation, then it will have the axis of 

 its magnetic field identical with the axis of rotation, which is 

 the chief approximate fact of the earth's magnetism. The 

 actual obliquity of the magnetic to the rotational axis is traced 

 to unsymmetrical magnetic permeability of the earth, which also 

 •causes the induction of earth currents, the secular variation of 

 whose tracks is the cause of magnetic secular variation. The 

 theory advanced to account for daily variation is that, under 

 the action of the sun's rays, the oxygen and ozone of the atmo- 

 sphere become the active substance of a large secondary battery 

 or accumulator, whose alternate charge and discharge are the 

 cause of the daily variations. 



The metamorphic rocks in Eastern Tyrone and Southern 

 Donegal have engaged the attention of Prof. Grenville Cole, who 

 has sought to determine the relative ages and relations of the 

 granites and gneisses {Trans. Royal Irish Acad., vol. xxxi. 

 Part ii. 1900). The oldest recognisable rocks in the two areas 

 are schists foliated by dynamic metamorphism. In Eastern 

 "Tyrone, the occasional gneissic character of this schistose series 



NO. 1619, VOL. 03J 



has probably been induced by the intrusion of a granite magma, 

 while the structures due to dynamic action have usually been lost 

 in the new flow-structures set up. The gneisses, as well as the 

 less altered schists, are traversed by and included in the granite 

 of the Slieve Gallion type, which also cuts an overlying basic 

 igneous series. In Tyrone, the older granitic material has not 

 been exposed, but it appears in Southern Donegal, and there the 

 granitoid gneiss is seen to be intrusive in an amphibolite series. 

 The pure quartz-felspar-muscovite gneiss becomes rich in biotite 

 at the junctions, and receives a foliated structure, which is due 

 to flow and not to pressure- metamorphism. Similar relations 

 have been observed elsewhere among the older metamorphic 

 rocks. The Irish rocks, to which attention is now drawn, may 

 all be of Archaean age, although the schists (termed Dalradian) 

 are probably the oldest nosv remaining in the district. After 

 referring to Dr. Callaway's researches in Galway, where he 

 showed how gneiss has been formed by the intrusion of granite 

 into a series rich in amphibole, the author remarks that his own 

 observations tend to confirm the opinion that gneisses may be 

 produced by admixture along surfaces of igneous contact, and 

 that in such cases contact-metamorphism occurs upon a regional 

 scale. Too often, however, the contact-phenomena on a broad 

 scale have been removed by denudation from the surface of our 

 granite domes, and we encounter them only in section along the 

 flanks of the igneous mass. 



The official report of the polar expedition of the Duke of the 

 Abruzzi is summarised in the Times. The following points are 

 of interest. The Stella Polare left Christiania on June 12, and 

 the farthest north point reached by it was 82° 4'. After this thet 

 party had left the ship and established themselves on Rudolf 

 Land. The Duke organised Short excursions inland, in pre- 

 paration for the great sledge expedition it was intended to 

 undertake later. During an excursion at Christmas time the 

 Duke and Cagni fell into a crevasse. The result of this was that 

 two fingers of the Duke's left hand were incurably frostbitten, 

 and the terminal joints had to be amputated. The shock of the 

 fall and of the amputation affected Jthe Duke's health so much 

 that the doctor considered he was totally unfit to undertake the 

 command of the expedition over the ice towards the Pole. Cap- 

 tain Cagni started on March 1 1 , with a party consisting of ten 

 officers and men, with numerous dogs and some sledges and 

 kayaks. After nine days' march, during which 43J miles were 

 made, Cagni, finding the provisions running short, sent back 

 Lieutenant Querini with two men. These three have not 

 been heard of since. On March 31, when the sledge expedition 

 had passed the 83rd parallel. Dr. Cavalli-Molinelli was sent back 

 with two men. This, with two sledges and sixteen dogs, ar- 

 rived safely at the main camp on April 24, having taken four 

 days longer to return than to go. Cagni, in the meantime, con- 

 tinued his journey with three of the Italian Alpine guides. They 

 were able to increase their speed to 9^ miles per day, and at last 

 they reached Nansen's furthest north, 86" 14'. After a long and 

 careful observation to make sure of this, they passed beyond, 

 and on April 26, 1900, they touched 86° 33' N. at about 56° E., 

 when they decided to turn back. No land was in sight, nothing 

 but ice in a state of thaw. Petermann's Land, which Payer be- 

 lieved he saw, did not exist where he stated, otherwise Cagni 

 would have seen it early in his journey. The same is said of 

 King Oscar Land, which would otherwise have been seen on 

 the return march. 



We have received the November number of the Entomologist's 

 Monthly Magazine, which contains notes on the occurrence in 

 Britain of several rare Lepidoptera during the past summer. 



The Transactions of the Hull Scientific and Field Naturalists' 

 Club for 1900 contain a number of papers and notes dealing 

 with local natural history and antiquities, among which may be 



