July 29, 1880] 



NA TURE 



ceived that when the absorbent sodium-vapour was very dense 

 and the dark line very broai a pecuUar bend outwards appeared 

 in the spectrum at the ends, and on opposite sides, of the line. 

 The cone of sodium vapour in the Bunseu flame acts as a prism 

 with upward horizontal refracting edges. If glowing sodium 

 vapour give dispersion, this cone should give, with horizontal 

 rays passing through it, a vertical (though necessarily impure) 

 spectrum ; and if the rays have also passed through a glass 

 prism with horizontal refracting angle, a spectrum of the form 

 above described should be got. From the position, the refractive 

 index of the vapour is greatest for tho^e rays which are most 

 deflected downwards. In agreement with the author's researches 

 on solid bodies and liquids, the refractive index increases greatly 

 as you approach the band from the red side, is less on the green 

 side than on the other, and then quickly increases again. If an 

 actual prism of glowing sodium vapour could be produced, one 

 might obsen'e, even with little thickness of vapour, indications 

 of anomalous dispersion in the narrow absorption lines. Herr 

 Kundt's attempts, however, to change the cone-shaped flame, by 

 means of lateral plates of glass or mica, to a prismatic one, led 

 to nothing. 



In a recent paper on the theory of inconstant galvanic ele- 

 ments ( Wicd. Anil., No. 6) Herr Exner contends that the so-called 

 galvanic polarisation in elements has no existence. The distinc- 

 tion between a Daniell and a Smee element is merely quantitative, 

 not qualitative. What does he mean ? 



GEOGRAPHICAL NOTES 

 We understand that a letter was received in London last 

 Saturday from a member of one of the Belgian Expeditions in 

 Central Africa, stating that he had met Mr. Thomson, with the 

 African Exploration Fund's Expedition, on May iS, at a place 

 .some ten days' march from Simba's, so that the party had evi- 

 dently found it necessary to return to the coa»t by the caravan 

 route to Bagamoyo or Saadani instead of following the original 

 plan of coming out at Ivihva. It is probable that the change of 

 route was necessitated by civil wars among the native tribes. 

 Mr. Thomson has thus had an opportunity, not contemplated 

 at the outset, of passing through a considerable tract of unknown 

 country between the south-east of Lake Tanganyika and Unyan- 

 yembe, and it is satisfactory to know that in so doing he has 

 been able to visit Lake Hikwa and settle its proper position, 

 w^hich has been a puzzle to geographers for some time. In a 

 map accompanying the account of Mr. H. B. CotteriU's journey 

 with the late Capt. Elton northwards from the head of Lake 

 Nyassa, this lake is placed with dotted lines in a position which 

 is probably a good deal too much to the south and east of its 

 true locality. The letter above referred to added that Mr. 

 Thomson was in excellent health, and that he claimed to have 

 traversed 2,000 miles of unknown country in the twelve months 

 he had then been on the march. A telegram from H.M.'s 

 Consul-General at Zanzibar, dated July 17, announces the safe 

 return of Mr. Thomson and his party. 



Mr. Alfred Rabaud, president of the Marseilles Geographi- 

 cal Society, has just published (Marseilles : Barlatier-Prissat) a 

 brochure &sSXL\e.i. "L'Abbe Debaise et sa Mission geographique 

 et scientifique dani I'Afrique centrale," which is accompanied 

 by a photograph of the deceased traveller. 



Prof. R. J. Veth, president of the Dutch Geographical 

 Society, has just issued in Italian (Turin: Guido Cora), "Notizia 

 de Selajar et Isole Adiacenti," which is illustrated by an original 

 map of Selajar and other islands of the Celebes group, together 

 with a note by Signor Cora. 



The TravailUiir, with the French Government Expedition 

 for the exploration of the Bay of Biscay, left Bayonne on July 

 17, having on board MM. Milne-Edwards, father and son, 

 Vaillant, of the Natural History Museum ; Fischer, assistant 

 naturalist ; Marion of Marseilles, Fohn, Perin, and the English 

 naturalists, Dr. Gwyn JJeffreys and the Rev. Mr. Norman. The 

 results of the expedition may be described at the Swansea 

 meeting of the British Association. 



NEW SCHEME FOR DIRECTING BALLOONS 



]\/r GABRIEL YON, one cf the directors of the great 



• Giffard captive balloon, and Mr. E. A. Pearse of Bristol, 



have each published a pamphlet on the direction of aerostats. 



The balloon of each inventor is to be elongated according to the 

 principles of the experiments tried by Giffard in 1852 and by 

 Dupuy de Lome in 1871. The propeller is to be moved by a 

 gas-engine in the Pearse balloon, and by a steam-engine in the 

 Yon balloon. M. Yon proposes to use the gas of the balloon as 

 fuel, but only in proportion to loss of weight produced either by 

 uncondensed steam or by consumption of petroleum. 



Nothing can be said to be really impracticable in the Pearse 

 scheme, although Mr. Pearse lacks the aeronautical training 

 which distinguishes M. Yon, an aeronaut who ascended with M. 

 Giflard in 1S54, ind has witnessed all his experiments. The 

 only essential difference between M. Giffard's scheme and the 

 new system is the place given to the fan, which M. Giffard 

 attaches to the car. Practice will only decide whether the 

 alteration projected is an improvement or otherwise. The 

 reason alleged for the change is the bringing of the fan nearer 

 to the centre of resistance. But it obliges the aeronaut to give 

 to his fans a very small diameter, which requires an immense 

 number of rotations in a second, and consequently represents a 

 loss of power. 



The calculations appear to have been made with care by M. 

 Yon and Mr. Pearse. A trial would be greatly desirable, 

 although it is impossible to suppose that the aerial carriage 

 of Mr. Pearse or the directing balloon of M. You can possibly 

 bring aeronauts to the North Pole for their inaugural trip, they 

 may be instrumental in eliciting useful facts. We may add to 

 the peculiarities of M. Yon's scheme that he uses a small globe 

 inclosed in the lower part of the aerostat called a compensation 

 sphere, and connected by a pipe with a ventilator, for keeping 

 intact the form of his aerial machine. Mr. Pearse does not 

 appear to be convinced of the urgent necessity of abstaining 

 in any aerial construction from every complication which can be 

 avoided at any cost, and he suggests the adoption of some 

 accessory organs which, although designed to help aeronauts, 

 would tax too much the lifting power or the attention of the 

 aerial sailor. Mr. Pearse supposes that he will be able to navigate 

 the air with an excess of weight, and does not pay attention to 

 the intensity of motive pDwer required to counteract gravitation 

 even in a partial manner. He should certainly take advantage 

 of the pamphlet written by liis French competitor, who deals 

 mostly with facts belonging to the public, and on which nobody 

 can, in the present state of science, raise any claim as being his 

 own property. 



Both these pamphlets are greatly in advance of similar pro- 

 ductions, and are creditable to their writers. Mr. Pearse's 

 pamphlet has been only published for private publication, 

 jl. Yon's is printed with a number of plates representing many 

 details ; but a directing balloon is so complex a matter that this 

 part of the publication can hardly be said to be complete. 



Having been the builder of M. Dupuy de Lome's balloon and 

 one of his crew, M. Yon may be said to have witnessed all the 

 great aeronautical constructions of the age. Next to M. Henry 

 Giffard, of whom he claims to be the pupil, he is the most com- 

 pletely qualified aeronaut to work out the solution of the great 

 problem to which a recent success in photogi'aphy has given 

 unexpectedly in some respects a practical result. 



W. De Fonvielle 



EXPERIMENTS WITH THE WIRE TELE- 

 PHONE, CHIEFLY ON STRONGLY MAG- 

 NETIC METALS 

 T) Y a wire telephone is meant an instrument like that described 

 ■^ in N.VTURE, vol. xxii. p. 16S. In most of the experiments 

 mentioned below, the mercury cups there figm'ed were dispensed 

 with, as they are unnecessary when stout wires are used. A 

 small ear-piece with a ferrotype plate was also used instead of 

 the drum-head, whose special purpose was to reproduce music 

 so as to be audible at a distance. For hearing close at hand the 

 ferrotype plate is much superior ; indeed with the drum many 

 of the sounds alluded to below could not be heard. 



So far as I can see yet, the most probable cause of the sound 

 in the wire telephone, when fine wires of ordinary weakly 

 magnetic metals are used, seems to be variation of the longitudinal 

 tension arising from the variation of the heating effect of the 

 current. It is of covirse quite possible that there may be a 

 lengthening of the wire due to the passage of the current over 

 and above that arising from the heat developed, although such 

 an effect can scarcely be said to be certainly established by 

 experiment as yet. 



