28o 



NATURE 



\_7uly 22, 1880 



increased attention and care. M. Wurtz having resumed his 

 seal, M. Dumas presented a letter from Mr. Croolves, in which 

 he summarises liis theories of radiant matter, and submits them 

 for discussion before the French Academy. After having 

 explained the Crookesian view of the fourth state of matter, M. 

 Dumas added that he felt confident these assumptions would be 

 the occasion of discussions of the same character as that which 

 the Academy had just witnessed. 



PHYSICAL NOTES 



Herr Dorn of Breslau has published a fresh series of experi- 

 ments on the propagation'of electricity by current water in tubes, 

 and allied phenomena ( IVieii. Ann,, Nos. 4 and 5). In agreement 

 with Helmholtz's theory, he finds the electromotive force from 

 current water in capillary tubes independent of the cross section 

 and the length of these. The value of the "electric moment " 

 of water and glass (3"936 Daniell) deduced from this electrom.jtive 

 force corresponds nearly to that deduced by Helmholtz from 

 Quincke's observations on the propagation of water in glass 

 tubes by the electric current. Observations of the electric current 

 produced by water flowing in capillary tubes lead to a somewhat 

 smaller value. For w ider tubes (within pretty wide limits) the 

 current strength, with a given mean velocity of the streaming 

 water, proves empirically to be nearly proportional to the radius 

 of the tube. Traces of a sliding of the water on the glass-wall 

 may perhaps co-operate in producing the variations of electro- 

 motive force observed in course of time. Through motion of 

 material particles in a liquid, therefore, an electric current arises. 



The diffiision of salts in aqueous solution has been investigated 

 by HeiT Long ( H'ied. Ann., No. 4), by a method similar in 

 principle to that of Schuhmeister (though different in detail), viz., 

 making a continuous water-cun-ent ilow over the salt solution 

 and measuring the amount of diffusion by the quantities of salt 

 that pass over in given times. Various interesting relations were 

 found, e.g., tlie chlorides, bromides, and iodides of the alkali 

 metals form a series, in which NH4 stands between K (the 

 higher) and Na ; and KCl, KBr, KI, and KCy have nearly the 

 same velocity of diffusion. Such is the case also with the corre- 

 sponding NHj and Na salts and with the chlorides of the bi- 

 valent metals Ba, Sr, Ca, and Mg, the nitrates, and tlie 

 sulphates. It seems generally that those salts which diffuse most 

 quickly also conduct best in aqueous solution. Salts with large 

 molecular weight and volume seem to diffuse most easily, while 

 among the waterless salts those which absorb most heat in dis- 

 solving or (the same thing) whose molecules, through the work 

 done, finally reach the finest state of division, have the greatest 

 velocity of diffusion. The chlorides of the alkalies stand in the 

 same series with regard to molecular volumes, velocities of dif- 

 fusion, conductivity, and absorption of heat. This is the case, 

 too, with the corresponding bromides and iodides. Cyanide of 

 potassium behaves as to diffusion and conductivity exactly like 

 the chloride, bromide, and iodide of the metal. In the second 

 group (nitrates) the order is the same as to conductivity and dif- 

 fusion ; but with regard to molecular volumes and heat-absorp- 

 tion the salts form a special series. In the group of sulphates 

 the individual salts have the same order as to diffusion and con- 

 ductivity, but the values for molecular volume and heat of solu- 

 tion are quite irregular ; indeed as regards velocity of diffusion 

 and absorption of heat the waterless salts seem to stand in 

 inverse order. These results are fully discussed by Herr Long. 



A CURIOUS physical phenomenon has been lately described by 

 Dr. Grassi (Rcale 1st. Lomb. Rend., f . viii. and ix.). An apparatus 

 is formed of three concentric vessels with an annular space of 

 about two centimetres between the first and the second, and the 

 second and the third. The outer space is filled with oil, the next 

 with water. The oil is heated by a gas furnace to a little over 

 100°, and the water boils. Then hot oil, at e.g., 150° is poured 

 into the central space. This quickly cools to a temperature close 

 on 100°. Dr. Grassi found that the central oil cooled more 

 rapidly the higher the temperature of the outer oil ; and with 

 more delicate apparatus (in which the vaporised water was con- 

 ducted and returned, and the outer oil kept at any required constant 

 temperature) he arrived at definite numerical results, which he 

 tabulates. With the outer oil at a mean temperature of l29°-9, 

 e.g., the time of cooling of the inner oil from 130° to 1 10° was 

 49s. ; when the former was lo5°'i, the latter was S7s. Alcohol 

 and ether gave more decided results. The maximum difference 

 was got with ether; the outer oil being at 57'5°, the inner took 



25s. to cool from 57° to 50° (7 degrees) ; whereas the former being 

 39'.3'', "le latter became 39'5s. In all the experiments the 

 cooling of the inner oil commenced at a temperature little above 

 the maximum of the external oil. When the outer oil is at a 

 higher temperature, at a certain point the heat begins to prevail 

 which is transmitted directly from the outer to the inner oil. An 

 analogous phenomenon (to which Dr. Grassi refers) was that ot 

 some members of the Accademia del Cimento, who found that 

 water in a vessel surrounded by ice cools more rapidly if the ice 

 be heated to accelerate fusion. 



Dr. J. PULUJ lately communicated a paper to the Scientific 

 Club of Vienna on "Radiant Electrode-matter," in which he 

 traverses the researches of Crookes, Hittorf, Goldstein, and 

 others upon the phenomena of electric discharges in high vacua. 

 He maintains at the outset that the discharges of "radiant 

 matter" observed by Crookes at the negative pole are not 

 residual gas at all, but .are particles of metal torn off from the 

 surface of the pole. He thinks this proved by the mirror-like 

 deposits of metal that are formed on objects interposed in the path 

 of the discharge. That aluminium in this way forms no mirror 

 is a difficulty in the way of this theory ; but Dr. Puluj gets over 

 this by remarking that the cause of this lies in the chemical 

 constitution of the metal, and that the particles of an aluminium 

 electrode fly round so far that they deposit themselves on the 

 electrode ! All the magnetic effects of these discharges Dr. 

 Puluj regards as explainable by ordinary electro-magnetic laws, 

 assuming that a stream of electrified matter acts as an electric 

 current ; but he apparently is not acquainted with the theoiy put 

 forward by Maxwell on this point. Dr. Puluj has also constructed 

 what he calls an electrode-lajnp, which gives a bright light when 

 worked by an induction-coil capable of affording a spark of 

 10 cm. length. In this lamp the radiant discharges of electrode- 

 matter are concentrated upon a piece of carbon which glows 

 w ith a white heat, but remains unchanged and unconsumed. 



Dr. Cusco, ophthalmic surgeon in one of the hospitals of 

 Paris, has invented a lens of variable focus, in which the pressure 

 of a column of water or other transparent liquid is made to alter 

 the curvature of the flat faces of a cylindrical cell of brass closed 

 witli thin glass disks. The pressure can be regulated by a 

 manometer gauge to any required degree within the limits of 

 working. It is said that the lens gives a sharp, well-defined 

 focus. It is constructed for Dr. Cusco by M. Laurent. 



M. Henri Becquerel continues his researches on the mag- 

 neto-optic properties of gases. He has recently examined the 

 gases oxygen, nitrogen, carbonic dioxide, nitrous oxide, and 

 olefiant gas, and finds that, except in the case of oxygen, the 

 magnetic rotation of the plane of polarisation due to a field of 

 given intensity varies inversely as the square of the wave-length 

 of the r.ay, as is the case with solids and liquids. In an older 

 research of Becquerel's it was shown that for non-magnetic solids 

 and liquids the rotation R was proportional to a function of the 

 refractive index «, very nearly represented by the expression 



R 



n-{n- - i) ; or, in other words, the quantity— — = = e. For 



>i-(n' — I) 

 all non-magnetic solids and liquids the value of c lay between 

 o'26 and o'$g. In the case of gases in which the rotation is but 

 a ten-thousandth part of that of most solids or liquids the same 

 result holds good, and the values of c for gases fall between o'26 

 and o'59. The above law, that the magnetic rotation is inversely 

 proportional to the square of the wave-length, implies that violet 

 rays are more rotated than the red ; or, in other words, that 

 there is a positive dispersion. In the case of oxygen it is found 

 that the red rays are rotated more than the green, affording an 

 inverse or negative dispersion. This is the more curious as 

 oxygen gives a positive'rotation as if it were a diamagnetic body. 

 In fact, Becquerel remarks, oxygen behaves as if it were a mix- 

 ture of a magnetic and a diamagnetic body, the magnetic having 

 small negative rotation and great negative dispersion, the dia- 

 magnetic having great positive rotation and small positive 

 dispersion. 



GEOGRAPHICAL NOTES 



In a private letter addressed to Herr von Hesse-Wartegg, the 

 well-known explorer. Dr. Naclitigall, writes from Berlin : — "The 

 German African Society (Deutsche Afrikanische Gesellschaf t) has 

 at the present moment not less than six different expeditions 

 travelling through Central Africa. The large funds necessary 

 for the outfitting of these numerous tr.avellers are raised partly 



