2^2 



NA TURE 



[July 12, 1S94 



composition of the dead floating masses gives rise to farther 

 pollution. An examination of the habits of this plant appears, 

 therefore, highly desirable in the interests of the inland fisheries. 

 The judges are Drs. Fleischer, Kbnig, Tiemann, Hermann, 

 Nitsche, Virchow, Hulwa, Kirchner, Magnus, and Weigelt. 



AN investigation by Prof. W.J. Sollas, F.R.S., "On the 

 Relation of the Granite to the Gibbro of Barnavave, 

 Carlingford" {Trans. Royal Irish Academy, vol. xxx. 

 pan xii. 1S94), his aided facts of considerable importance to 

 whit was previously known about the mountain groups of 

 Carlingford and Slieve Gullion, which rise from the centre of 

 the Palaeozoic tract of the counliei of Lough and Armagh, and 

 represent the remains of extinct volcanoes of the Tertiary period. 

 From an examination of the district, and a study of rock- 

 sections from it, the following statements are deduced :— (i) 

 The ga')bro of the Carlingford district is older than the granite 

 which penetrates it. (2) The gabbro was alreidy completely 

 solid, traversed by contraction joints, and, probably, fractured 

 by earth movements before the injection of granophyric material. 

 (3) The granophyric material was in a sta'.e of great fluidity at 

 the time of its intrusion. The granophyric dykes arc in no 

 case contemporary veins. The results of the investigation 

 suggest to Prof. Sollas some reflections on the diflficult question 

 of the "differentiation of originally homogeneous igneous 

 mignas." In his opinion, "much more attention must be given 

 to the investigaiioi of the de:ails of the now prevalent differ- 

 en'iation hypothesis before it can be regarded as established on 

 a firm basis." In fact, the importance of this paper as a con- 

 tribution to physical geology is liable to be overlooked, owing 

 to the topographical nature of its title ; but it soon becomes 

 apparent to the reader that the close intermingling of rocks of 

 different composition which has taken place at Barnavave, is 

 not likely to be an exceptional occurrence. The proofs of 

 microscopic penetration of the gabbro by the granite, until a 

 bulk-analysis of any sp;cimen would be most misleading, are 

 interesting to all geologists, and practically open a new field of 

 observation. A severe blow is struck at the whole theory of 

 "segregation veins," or "contemporary veins," which has 

 perhaps been maintained too academically and without com- 

 plete confirmation in natural exposures. It is worth noting 

 that this memoir is issued separately by the Royal Irish 

 Academy, like all published in their Transactions. 



In a paper published in the Ekclroltchnische Zeilsckrijl, in 

 which he described a new form of gas voltameter. Prof. Kohl- 

 rauich expressed his sarpnse thr. the gis voltameter was so 

 sellom used for measuring currents. The reason for this state 

 of affairs is probably to be found in thit the form of gas volta- 

 iDcter ordinarily in us; is b )th inaccurate and troublesome to 

 use A new form of gas voltameter has recently been devised 

 by Herr II. A. Niber, of Amsterdam, which embolics several 

 improvements. The burette in which the gas evolved (either 

 hydrogen or oxygen) is collected, can be turned about a vertical 

 %x\s so as to bring its lower end over the electro le, and thus 

 start or stop (he c illection of gas at any given time without 

 breaking the current passing through the voltameter. By means 

 of an auxiliary vessel into which air cin be driven, the level of 

 the liquid inside and outside the burette can be made the same, 

 so that there is no correction to be applied to the barometric 

 pressure in order to find the pressure under which the gas is 

 measured. The burette is fitted with a (ap, so that the oxygen 

 Of hydrogen evolved can be passed into another vessel and 

 collected. The whole of the apparatus is constructed of glass, 

 except, of course, the electrodes, which are of platinum, and are 

 to arranged that the two gasei evolved can never possibly mix, 

 and thus cause an explosion, if by any chance the platinum of 

 the eleclrodei becomes exposed to this mixture of gases. 



NO. 1289. V OL. 50] 



A NEW form of automatic steering compass has been invented 

 by Lieut. Bersier, of the French Navy, and a very full descrip- 

 tion is published in La Nature for June 25. The difficulty 

 with any form of automatic compass is that any arrangement by 

 which the compass card mikes or breaks a mechanical contact 

 when the course deviates from a straight line will interfere with 

 the free set of the needle. Lieut. Bersier, in his compass, uses a 

 spark from a Ruhmkorff coil, which passes between a metal 

 point on the edge of the compass'card and one of two semi- 

 circular metal plates fixed to and insulated from the sides ol 

 the compass bowl. These metal plates are connected to two 

 small electromagnets, and when the electric current which forms 

 the spark passes, it closes the circuit of a small motor which 

 actuates the steering gear. If the spark passes to one plate 

 the motor ss-orks in one direction, while if the spark passes to 

 the other plate the motor works in the reverse direction ; so that 

 it is only when the point on the card is half-way between 

 the two metal [plates that the rudder is amidships. It is said 

 that the ne.v compass has been tried in the French Navy for 

 several months pist, and has given entire satisfaction, which, 

 considering the very delicate and complicated nature of the 

 mechanism employed, is veiy remarkable. The new form 

 of compass can be made to automatically register the course 

 steered, the spark being caused to pierce a band of paper which 

 is moved by clockwork. 



I.v a short paper communicated to the Johns Hopkins 

 University Circular, Mr. .\. S. Mackenzie describes some 

 experiments he has conducted to test the validity of the New- 

 tonian law of attr.iction for crystalline and isotropic masses at 

 small distances. In discussing the elastic solid theory of re- 

 fraction in physical optics, it is often customary to introduce an 

 optical density which may be different in different directions. 

 In uniaxal crystals there are two such directions, and in the 

 case of Iceland spar the square roots of the densities are as 

 I '486 to I '658. Thus the question arises, does this property 

 depend upon the distribution of the mass with reference to the 

 optic axis? and if so, could a crystal attract a pirticle in a 

 manner dependent upon the position of the particle with reference 

 to the optic axes of the crystal, so that it would act as if it were 

 of greater mass (and therefore density) in one direction than in 

 another? It is to elucida'e this point that the author has been 

 conducting a series of experiments, using for this purpose a form 

 of apparatus which, at any rate as far as the magnitude and sus- 

 pension of the attracted misses are concerned, resemble; that 

 used by Prof. Boys. The apparatus, however, is designed for 

 relative rather than absolute measurements. .Mihough the 

 greatest divergence between any two results only amounted to 

 I part in 200, no difference in the attr.iclion of a crystalline mass 

 along, and at right angles to, the axis was discovered. A second 

 set of experiments was undertaken in which the attracting masses 

 were isotropic, but in which the distances between the attractinj; 

 and attracted masses was varied, with a view of testing the law 

 of the inverse square of the distance. The form of apparatus 

 used seems particularly ill-suited to test this point, as the dis- 

 tances between the centres of the masses are very hard to 

 measure. The author, however, says these distances could be 

 measured to within /, mm , and he finds that while the de- 

 flections .as calculated, assuming the correctness of the inver-e 

 square law for dis ances of about 74, 55 and 36 cm. between 

 the centres of the large and small masses were as I :2'05 : 5'*5> 

 while the observed deflections were as i : 2 '04 : 5 '24. So that 

 the Newtonian law has been found to be true for the attractions 

 of non-isotropic, and for istropic masses at distances apart as 

 small as 3 or 4 cm. 



In the Afodcrn Medicine and Baeleriologicai Review for May, 

 attention is called to a subject which is attracting special in- 



