570 



NA TURE 



{April 



12, I 



Near j8 Serpentis 

 From Hercules... 

 From Vulpecula 



R.A. 



232 



255 

 268 

 272 

 300 



Meteor- Showers. 

 Decl. 



17 N. 

 37 N. 

 33 N. 

 20 N. 

 24 N. 



Very swift. 

 April 12-25 

 Lyrids, April i8-20 

 April 18-24 

 April 19-20. Swift 



Very 

 swift. 



GEOGRAPHICAL NOTES. 



The Russian Geographical Society elaborated at its last meet- 

 ing the following programme of work for the next summer. 

 M. Kuznetsoff will continue his geo-botanical work on the 

 northern slope of Caucasus, and M. Rossikoff will continue his 

 survey of the Caucasian glaciers on the little-known southern 

 slope of West Caucasus. M. Listoff will also resume. his explora- 

 tion of the caves containing layers of ice in Crimea. Pendulum 

 measurements will be done by Prof. Sokoloff in Poland and 

 West Russia ; and an Expedition'of three persons will be sent 

 out for the exploration of the Kola peninsula. 



The following details of the Brazilian Expedition, headed by 

 Dr. von Steinen, have been received from Dr. Ehrenreich, one 

 of the members of the Expedition. Their object was to investi- 

 gate the Kuluene River, a tributary of the Xingu. Dr. Ehrenreich 

 gives the following as the chief results of the Expedition : (i) 

 the discovery of great Caribbean races in the centre of South 

 America, named respectively the Bakairi and the Nahugua'; 

 (2) the discovery of the Kanayura and Anite tribes, who still 

 speak the ancient Tupi language, and use remarkable weapons, 

 amongst which is the very peculiar arrow fling. Surveys of the 

 Kuluene were made and many ethnographical specimens have 

 been collected, forming a complete picture of the original culture 

 of these Indians, who, even to-day, do not know the use of metal, 

 but are still in the period of implements made of flint, bone, and 

 fish teeth. 



OUR ELECTRICAL COLUMN. 



J. T. 'BoTTOMLEY showed that the temperature of a wire 

 conveying electric currents varied with the air-pressures sur- 

 rounding it, and that a wire which remained dull 'at ordinary 

 atmospheric pressure incandesced when a moderate vacuum was 

 obtained. M. Cailletet has been working in the opposite direc- 

 tion. He has shown that a current which would fuse a wire 

 under ordinary pressure will scarcely raise it to redness when the 

 pressure is sufficiently great. These experiments show how 

 essential free convection as well as radiation is to the incand- 

 escence of filaments in glow-lamps, as well as to the heating of 

 conductors. 



Lecher {Rep. der Physik, xxiii. p. 795) has experimented on 

 the much-vexed question of the counter-electromotive force of 

 arc lamps, and he finds that its existence is not proved, that the 

 observed difference of potential which is expressed by the formula 

 a + bl varies with temperature, and that it is probably due to 

 discontinuity in the current. 



Considerable attention has lately been devoted to the 

 potential difference between the various constituents of a voltaic 

 cell by direct measurement, an operation facilitated by Helm- 

 holtz's capital observation that this difference between an elec- 

 trode of mercury flowing in drops through a capillary tube and 

 an electrolyte is nothing. The mercury thus acquires the 

 potential of the electrolyte, and can be measured. Moser 

 (Beibldtter, xi. p. 788) has thus measured the Daniell and 

 Clark cells, and Miesler has been fallowing it up. Thus in 

 the Daniell cell — 



Zn I ZnS04 = -I- I '06 volt 

 ZnS04 I CUSO4 = + -22 ,, 

 CUSO4 I Cu = - -22 ,, 



Total PD ... I 06 „ 

 In the Grove cell — 



Zn I H2SO4 = -I- i-o6 volt 

 H2SO4 I HNO3 = + -36 „ 

 HNO, Pt = + -20 ,, 



He makes the PD — 



C I HNO3 = + "38 volt 

 C I H2Cr04= -F -62 „ 

 H2SO4 I H2Cr04 = -f -5 „ 



PbOj I H2SO4 = + i-Z „ J 



H2SO4 I Pb = -1- -9 „ 



all the measurements, except that of the Grove cell, according 

 fairly well with known and accepted measurements. 



Hertz, Wiedemann, a.nd Ebert have been experimenting 

 on the influence of rays of high refrangibility on electrical dis- 

 charges, and M. Hallwachs has been verifying their results. He 

 finds that a well-insulated disk of zinc charged with electricity 

 rapidly loses its charge when the rays of an arc lamp fall upon 

 it. It is more rapid with negative than with positive charges. 



TEND UL UM SEISMOME TERS. 

 PENDULUM SEISMOMETERS are among the oldest forms 

 of instruments employed to record earthquake motion upon 

 a stationary plate. In 1841 crude forms of such seismometers 

 were used to record shocks at Comrie in Scotland. The ob- 

 jections to the older forms of these instruments are that they are 

 not provided with any arrangement to magnify the motion of the 

 earth, the writing indices are not sufficiently frictionless, and the 

 value of the records are destroyed because the pendulums almost 

 invariably swing (see "Experiments in Observational Seismo- 

 logy," by J. Milne, Trans. Seis. Soc, vol. iii. p. 12). The 

 first pendulum seismometer with which I am acquainted which 

 has a multiplying index is the one described, constructed, and 

 successfully employed by Dr. G. Wagener (see Trans. Seis. 

 Soc, vol. i. p. 55). From Dr. Wagener's account of this in- 

 strument it was the inventor's intention to counteract any 

 tendency of the pendulum bob to swing by the inertia of the 

 multiplying index, and from his experience with the instrument, 

 owing to frictional resistance or otherwise, it seems that even 

 if the pendulum was set in motion it quickly came to rest. 



The multiplying arrangement, or "indicating pendulum," in 

 Wagener's instrument was a lever, which we will call a b c, 2$ 

 inches in length (Fig. i) ; the upper end of this at a geared 



Total PD 



1*62 



in the base of the main pendulum bob w by a ball-and-socket 

 joint. One inch below, at b, a second ball-and-socket joint con- 

 nected the lever with the earth. Now i( a remained at rest, and 

 b, being connected with the earth, moved backwards and for- 

 wards, a multiplied representation of this movement was pro- 

 duced at c, 24 inches lower down. The question which arises is 

 whether w tends to remain at rest, and what effect the jointed 

 system a b e exerts upon it. 



Imagine that an impulse is received towards the right, so that 

 the point of suspension of w at 0, and the point b, move to the 

 right. The tendency of w is therefore to move to the right. If 

 the centre of oscillation o{ a b c relatively to 3 as a centre of per- 

 cussion is below b, then a will move to the right and assist w in 

 its swing ; if, however, the centre of oscillation is above b then 

 w will be retarded in its motion. In Dr. Wagener's instruments 

 the centre of oscillation was below b, and hence the index re- 

 tarded w by its inertia and friction only. Still, the instrument was 

 the first one where there was an attempt to use an " indicating 



