April 13, 1899] 



NA TURE 



563 



Devonian or Carboniferous ; (2) the physical modifications pro- 

 duced in minerals by pressure ; (3) the organisation and de- 

 velopment of the platoda ; (4) the presence of a nucleus in the 

 Sehizophyta ; and (5) the Devonian flora of Belgium. 



M. P. ViLLARD, writing in the Journal de Physique for 

 March, continues his observations on kathodic rays. Among 

 other interesting conclusions, the author is led to the view that 

 hydrogen plays a prominent part in the production of kathodic 

 rays ; this view explains the action of these rays in reducing 

 oxides. 



M. d'Ocagne's system of " abaques" is remarkable for the 

 number of problems it enables the mathematician and the 

 physicist to solve graphically. An interesting application of the 

 method is given by M. A. Lafay in a recent number of the 

 journal de Physique, where Fresnel's laws of reflection and 

 refraction are represented by means of " abaques." 



In a note communicated by M. E. Carvallo to the founial de 

 Physique for March, on Clausius' theorem, the author points 

 out that although abundant proof is given in te.xt-books that for 



a reversible cycle la'Q/T = o the property that this integral is 



negative for irreversible cycles receives scanty demonstration. 

 The author considers it desirable that this question should be 

 more fully considered in elementary courses than is usually done, 

 and points out that this can best be effected by a more or less 

 detailed consideration of the different transformations which 

 lead to irreversible cycles. 



Dr. Rudolf Mewes has published a second edition of his 

 pamphlet on " Licht-, Electrizitats-, and X-Strahlen," of which 

 the first edition appeared in i8g6. The vast literature on 

 Rontgen rays which has accumulated during the past three years 

 has rendered it necessary for the author to restrict his attention 

 to researches bearing on the analogy between Rontgen rays on 

 the one hand and light and electric waves on the other, both in 

 their nature and in their fundamental laws. The author in an 

 appendix also discusses an application of the wave theory to 

 the problem of gravitation. 



Under the title "Two discharges derived from one con- 

 denser," Prof. A. Roiti, writing in \\\eAttidei Liitcei, viii. i, de- 

 scribes the phenomena produced when a condenser, charged by an 

 electrostatic machine working uniformly, is connected, by means 

 of two pairs of coils, with a Rontgen ray tube on one hand and 

 a spark gap on the other, the two being arranged in parallel. By 

 varying the self-induction of the coils and the length of the 

 sparking gap, the two discharges are made to take place simul- 

 taneously, and the intensity of the Rontgen rays is made a 

 maximum ; and Prof. Roiti gives a mathematical investigation 

 of the results observed in his experiments. 



In the Proceedings of the Philosophical Society of Glasgow, 

 Dr. W. J. Fleming describes a simple and inexpensive method 

 of localising with Rontgen rays. This, like other methods, is 

 based on the measurement of the distance apart at which two 

 images are produced by rays impinging on the object in two 

 directions at known angles to each other. The advantage of 

 the stand described by Dr. Fleming is that it enables the tube 

 to be rotated on two axes crossing at the centre of the anode, 

 the point from which the rays proceed. In this way it is pos- 

 sible to make the slanting surface of the anode face in any 

 direction in which it is desired to project the rays, without 

 affecting its position ; while the change of position of the tube 

 can be effected separately by moving the supporting stand, and 

 can be readily measured. 



The annual report of the Institute of Jamaica states that an 

 almost complete series of the thirty-five known species of 

 NO. 1537, VOL. 59] 



Jamaica actiniaria, collected by the curator, Mr. J. E. Duerden,. 

 has been placed on exhibition. A large series of sponges, con- 

 tributed by the Caribbean Sea Fisheries Development Syndicate, 

 constitutes almost the beginning of the local collections in this 

 group. One compact massive sponge is two feet in diameter. 

 A 3 to 5 pc cent, solution of formalin has now been employed 

 for over two years as a preservative fluid for fish, cretenterates, 

 holothurians, &c. , and has proved satisfactory, preserving the 

 natural form and colours of the animals better than alcohol. A 

 polished slab of mahogany, four feet in diameter, has been 

 added to the collection of woods, and illustrates the irregular 

 increase in thickness of tropical trees, as compared with the 

 regular annular rings in dicotyledons of temperate parts. New 

 types and many duplicate examples of relics of the aboriginal 

 Indian inhabitants continue to be received and added to the 

 already large collection on view and in store cases. 



Messrs. E. H. Hall and C. H. Ayres contribute to the 

 Proceedings of the American Academy of Arts and Sciences a 

 determination of the thermal conductivity of cast iron. In their 

 experiments a disc of cast iron was coated with an electrolytic 

 deposit of copper on its two faces, and the difterence of temper- 

 ature of the faces recorded by galvanometric readings depending 

 on the thermo-electromotive forces of the two couples thus 

 formed. Water at different temperatures was made to flow 

 across the two copper faces, and the total flow of heat measured 

 by comparing the differences of temperature between the water 

 entering and leaving the vessels. The thermal conductivity of 

 the cast iron used was found to be about o'i49o at 30" C, its 

 temperature coefficient being about -O'O0O75 between 20° and 

 75°. The electric conductivity of this sample was about 

 112,200 C.G.S. units, its temperature-coefticient between 17° 

 and 67° being about -oooiiS. The method used is thought 

 by the authors to be capable of giving better results than have 

 yet been obtained by it. 



In these columns frequent reference has been made to Dr. 

 Folgheraiter's researches on the magnetisation of ancient vases, 

 from which the author long ago advanced the hypothesis that 

 the magnetic dip had changed sign within historic times at 

 the places where these vases were made. The evidence on this 

 point, derived from examination of Grecian vases in the 

 Museums of Florence and Syracuse, forms the subject of the 

 most recent paper of the series published by Dr. Folgheraiter in 

 the Atti dci Lincei, viii, 5. Some of the vases, owing to the 

 ornamentations and projections above their mouths, could only 

 have been placed in the furnace in an upright position, and 

 although the presence of these projections rendered it necessary 

 for Dr. Folgheraiter to restrict his observations to the bases of 

 the vases, [the sign of the magnetic dip, if not its magnitude, was 

 readily determinable. Dr. Folgheraiter concludes (i) that at 

 the commencement of the period of fabrication of the 

 Corinthian vases and of the Attic ones with black figures on a red 

 background. (seventh century B.C.), the magnetic dip in (ireece 

 was austral ; (2) that shortly afterwards, perhaps at the beginning 

 of the sixth century, while Corinthian vases were still being 

 made, the magnetic dip was nearly zero, and then became 

 boreal ; (3) that at the end of the period of fabrication of the 

 Attic vases (about 400 B.C.) the magnetic dip was boreal and 

 amounted to about 20°. 



Among the latest results obtained by Drs. B. Grassi, A. 

 Bignami and G. Bastianelli, regarding the propagation of 

 malaria by mosquitos, the following conclusions are stated in- 

 their paper in the Atti dci Lincei, viii. i. (i) The hcemo- 

 sporids of malaria undergo in man the well-known life-cycle 

 characterised by the long duration of the ameboid phase and. 

 the absence of incapsulate stages ; in this cycle they are re- 

 produced an indefinite number of times, but also give rise to- 



