3IO 



NATURE 



{_Feb. 14, 1878 



where they will be installed in the Zoological Garden?, The 

 enterprising authorities of the Paris Zoological Gardens contem- 

 plate, moreover, importing some specimens of North American 

 Indians, their plan evidently being to keep up a kind of anthro- 

 pological review of the various civilised and semi-civilised peoples 

 of the globe. 



The German War Department has recently carried out some 

 experiments on a large scale with the electric light at Metz, in 

 order to test its practicability for military purposes. One of the 

 largest known electric lanterns was used for the trials, and it was 

 found possible to distinguish small detachments out of rifle-shot 

 with sufficient accuracy to direct on them artillery fire. 



The alarming rapidity with which shortsightedness is increasing 

 among German students formed the subject of a recent debate 

 in the Prussian Parliaoaent. From extended observations made 

 in the gymnasia, it appears that the number of the shortsighted in- 

 creases from twenty-three per cent, in the first year to seventy-five 

 per cent, in the ninth or last year. The too-frequent custom in 

 Germany of forcing lads to study during the evenings with in- 

 sufficient light, in ill-ventilated rooms, is undoubtedly a main 

 cause of this widespread evil. 



" Heroes of South African Discovery," by M. D'Anvers, that 

 we referred to in our last number, will be published, we under- 

 stand, next week by Messrs. Marcus Ward and Co. This volume 

 will contain an account of Stanley's expedition, and the accom- 

 panying map will show the route taken by that discoverer. 



The Societe d'Hygiene of Paris is making arrangements to 

 establish, in the cities and towns of France, chemical laboratories 

 for the purpose of examining articles of food and detecting 

 adulterations or unhealthful constituents. In this respect 

 France is, like Germany, following the example of England, 

 where the value of public analysts has long since been satis- 

 factorily demonstrated. 



While of course the thermo-electric pile is the most useful 

 measuring apparatus in investigations on radiant heat, it is pos- 

 sible, M. Violle suggests {Journal de Physique) to repeat easily 

 all fundamental experiments with the radiometer ; by moving it 

 along the spectrum one may readily show {even with the Drum- 

 mond light) the distribution of the heat in the luminous part and 

 jn the infra-red region. The action of coloured glasses, the 

 absorption of heat by water, in layers of different thickness, and 

 all similar phenomena, can be shown without any difficulty. 

 The beam of light employed falls directly, or after passage 

 through the absorbent substance, on the radiometer, the image 

 of which is, by means of a lens, thrown on a screen. The 

 experiment is very distinct and pretty ; it may be rendered more 

 precise by adopting an arrangement for counting the number of 

 turns of the radiometer. M. Violle says he has had constructed 

 by M, Alvergniat a small radiometer for the purpose ; it is placed 

 on a Duboscq projection apparatus ; and the turns can be easily 

 counted on the screen. 



In order to determine the ratio of the specific heats of air at 

 constant pressure and constant volume (a value so important for 

 the doctrine of heat), M. Kayser has recently made fresh experi- 

 ments on the velocity of sound in tubes. He adopted Kundi's 

 method ; in tubes of different diameter, air waves were produced 

 by means of a transversely vibrating rod, and the length of these 

 was measured by the dust figures remaining on the tube. Five 

 tubes of different width were used, and three different steel rods. 

 The results of the inquiry are these : (i) The velocity of sound 

 in tubes depends on their diameter and on the pitch of the tones, 

 and the retardation of the sound is inversely proportional to the 

 diameter of the tubes, and the square root of the number of 

 >ibrations. (2) The velocity of sound in unconfined space is 

 accordingly at any rate greater than in tubes ; these experiments 

 showed it to be greater than 331-646 m. (3) The velocity 



of sound in free space can be calculated from that in tubes 

 when two tubes of different width are used; from these 

 experiments the value obtiined for it was 332 '5 m. (4) From 

 this the ratio of the specific heats of air at constant volume and 

 constant pressure is inferred to be = i '4106. 



Three experi(nents,madewitha view to find how weak induced 

 currents in the telephone would still suffice to give distinct per- 

 ceptions by ear, have lately been described to the Vienna 

 Academy by Prof Sacher, of Salzberg : i. The closed circuit of 

 the telephone was, for a length of 20 metres, placed parallel with 

 the insulated wire (cloth and wax) of an ordinary telegraph 

 apparatus. The (Morse) signals were given first by means of 

 six, then three, Smee elements. The induced currents gave a 

 distinctly audible effect in the telephone, so that the messages 

 could be understood. 2. The insulated wire was laid bare at 

 two points 20 metres apart, and the ends of a telephone wire 

 120 me'res long, and equally thick, were connected to it at 

 those points. Only a small portion of the current could have 

 passed through the thin wire in the telephone. Yet the tapping 

 was heard with sufficient clearness to enable one to understand 

 the message. (It is an advantage to use a telephone at each 

 ear.) 3. A telephone wire about 40 metres long was connected 

 with the inner thick wire of an ordinary induction coil, and a 

 second telephone line, about 120 m. long, with the outer thin 

 wire. To Prof Sacher's surprise it was found possible to com- 

 municate through the first to the second telephone, and also 

 (somewhat better, it seemed) in the opposite direction ; and this 

 nearly as well as with direct connection. The words were per- 

 ceived more distinctly when two induction-coils were inserted 

 in the same way. The experiment did not succeed with a 

 Ruhmkorff. 



The improvement of the air-pump, which consisted in dis- 

 pensing with the flask-like receptacle (with stop-cock) as 

 employed by Otto v. Guericke and Robert Boyle, and intro- 

 ducing the much more convenient plate, is generally attributed 

 to Papin, This is shown by M. Gerland {Pogg. Ann., No. 12, 

 1878) to be a mistake. In Papin's first paper, " Nouvelles 

 Experiences du Vuide," &c., which appeared in Paris in 1674, 

 and which in 1 686 had become rare (the only two copies of it 

 now extant are in possession of the Royal Society, and in the 

 British Museum library), he describes and gives a figure of the 

 machine with which the experiments were made, and says : — 

 "Monsieur Hugens {sic) fit faire gette machine, ensuite celle de 

 M. Boyle, et il apporta divers changemens qu'on remarquera en 

 comparant leurs figures." This machine (whose figure M. Ger- 

 land reproduces) is the first which has a plate. Additional proof 

 that Huygens has the credit of the device is furnished by a letter 

 of Huygens himself, and the date at which the improvement 

 was introduced is shown to have been 1661. 



The Paris Jardin d'Acclimatation has just received a pair of 

 those peculiar Siberian hares, which are grey in summer and 

 white in winter, for the purpose of studying the effects of a 

 temperate zone on the changes of colour. 



The first telegraph line of the Chinese Empire has recently 

 been established between the arsenal of Tian Tsin atid the house 

 of the provincial governor. The constructor was Mr. Betts, the 

 director of the School of Mines of Tian Tsin. Although the line 

 is only some ten kilometres in length yet its construction marks 

 a new epoch in the administration of the Empire. The Great 

 Northern Telegraph Company, in spite of repeated efforts made 

 at Foo Chow, have not succeeded in obtaining the permission of 

 connecting this port with Amoy by a telegraph cable, and after 

 vainly trying for two years have finally given up the idea. The 

 line of Tian Tsin has, however, been constracted by order of the 

 Chinese Government ; and the population offered not the least 

 resistance wherever the telegraph poles were erected, A cable 



