October 12, 1893] 



NATURE 



57^ 



I'oland. The system of colouring adopted is, as far as possible, 

 that of the International Geological Map of Europe. The 

 quaternary de,50sits are omitted where they would much ob- 

 scure the solid geo'.ogy, but elsewhere they are shown. In some 

 parts, especially in Northern Russia, these superficial deposits 

 are thick and widely spread, so that the solid geology is not 

 known ; here it was necessary to show only these deposits. The 

 southern limit of erratic blocks is shown by a strong red line. 



MES5RS. Fletcher, Russell, and Co., the well-known 

 makers of gas appliances, have just introduced a new process to 

 supersede the use of Birlin black and black-lead for protecting 

 the cast-iron portions of their manufacture. The casting is 

 coated with a film of enamel, which is so thin that even the 

 finest details on the me:al are preserved. This enamel is said 

 to be absolutely proof against rust, and preserves its qualities at 

 any temperature up to a bright red heat. All Colours are 

 obtainable, including gold and silver, bright or dull, and as 

 many as are wished can be produced on one casting. The 

 process therefore o8fir5 great facilities for decorative work of all 

 kinds, and its protective qualities should ensure it a wide field 

 of usefulness. 



In a previous number of Nature (No. 1247) we published 

 the opening address by Mr. Jeremiah Head, President of Section 

 G, Mechanical Science. In this, among many of the mechanical 

 forces used by man, he referred at some length to the prospect 

 of 'man ever being capable of flying. Some very interesting 

 experiments, to which no allusion was made, although not bear- 

 ing directly on actual flight, may yet be found of sufficient 

 importance to be here related. For a very detailed account the 

 reader may be referred to No. 205 of the weekly journal, Prome- 

 theus. The experimenter in question is Herr Otto Lilienthal, 

 and his success in his so-called "flight" is the result of 

 much thought and considerable practice. The apparatus may 

 be described as a pair of large wings, similar in principle and 

 construction to those of a bird, with two tails at the back, one 

 placed vertically, and the other horizontally. The wings are 

 rigid and fixed, and no motive power at all is used ; the whole 

 apparatus weighs twenty kilograms. At the place where the 

 experiments have been carried on, a long sloping hill has been 

 used, with a platform raised about ten metres above the general 

 surface at the top, for the starting point. From this platform the 

 experimenter grips the apparatus between the wings or sails with 

 his hands, and springs off the edge. In the flight he descends 

 at an angle of about 10' to 15°, and the distance covered is some- 

 times very considerable. In the experiments carried on between 

 Rathenow and Neustadt he covered 80 metres, while from 

 another point he made a flight of 250 metres. The wind of course 

 plays an important part in these flights, but Herr Lilienthal 

 says that with practice one can steer the apparatus well. 

 With the wind blowing stronger on one wing than on the other 

 the equilibrium of the apparatus was found to be greatly dis- 

 turbed, but this was checked by the movement of the legs, which 

 changed the position of the centre of gravity. In these experi- 

 ments there is a great opportunity for gaining experience in 

 steering, and it seems very likely that we may learn much 

 thereby. 



The assumption, current some years ago, that the properties 

 of liquids change in proportion to the amount of matter held in 

 solution, has already been invalidated fjr the case of electrolytic 

 conduciivity. Messrs. F. Kohlrausch and W. Hallwachs, in 

 Wiedemann' s Annalen, publish some results showing that the 

 assumption is also erroneous in the case of density of dilute 

 aqueous solutions. The method adopted was the Archimedian 

 one of immersing a solid in the solution and noting its decrease 

 in weight. Errors due to capillarity were eliminated by attach- 

 ing the solid, a glass ball, to the suspending wire by means of a 



NO. 1250, VOL. 48] 



clean cocoon fibre. During mixing and stirring, the glass was 

 held in position by glass rings. The stirrer was one of mica or 

 platinum. Densities were observed up to 1-03, and the 

 weighings were reliable to within 0-2 mgr. provided that no dust 

 or fibres were attached to the cocoon thread. This gave a 

 limit of error equal to I in 10,000. Large variations of tem- 

 perature were corrected by a flame or ice, smaller ones by 

 calculation according to known formulae. All the bodies investi- 

 gated show a decrease of the ratio of condensation to concentra- 

 tion between o'ooj and 0'5 gramme-equivalents per litre. This 

 decrease amounts to I per cent, for sugar, 2 for hydrochloric 

 acid, 2-5 for common salt, 13 for phosphoric acid, and 20 

 or sulphuric acid. The correspondence between this change of 

 density and the change of electrolytic conductivity is very 

 apparent. Sugar, a non-electrolyte, shows the greatest 

 constancy of molecular density in solution. The authors intend 

 shortly to publish analogous results obtained in their investi- 

 gation of optical refraction. 



M. Van Aubel has continued his experiments on the re- 

 sistance of bismuth, and gives an account of the results he has 

 obtained in the Journal de Physique for September. The results 

 obtained are of special interest, as the use of spirals of bismuth 

 sdems to be the most convenient way of measuring powerful 

 magnetic fields, at any rate with a sufficient degree of accuracy, 

 for most industrial purposes. According to Righi, the electrical 

 resistance of commercial bismuth at 0° varies considerably, and 

 bismuth which has been compressed has its resistance less 

 affected by magnetism than that which has been melted. The 

 author in his experiments has made use of pure bismuth, pre- 

 pared by electrolysis according to the method he gave in his 

 former paper in the Annales de Chimie et de Physique, and his 

 observations show that neither sudden cooling nor compression 

 has much eStiX on the electrical properties of pure bismuth. 

 The resistance at 0° C. and the rate of change of the resistance 

 with temperature, and the strength of the magnetic field in 

 which it is placed, are almost the same, for rods that have been 

 annealed quickly cooled, or compressed. The resistance always 

 increases with rise of temperature, and between 0° and 100° the 

 change is very nearly regular. A mere trace of impurity, how- 

 ever, completely changes the properties of the metal. The action 

 of a magnetic field being the same, whatever the m jde of pre- 

 paration of the bismuth, it is better to use the spirals of 

 compressed bismuth rather than the more difficultly obtained 

 films of electrolytically deposited metal used by M. Leduc. 



In the current number of the Philosophical Afj^asine, Mr. 

 John Trowbridge has a paper on the oscillations of lightning dis- 

 charges and of the aurora borealis. By means of a rotating 

 mirror the author has photographed the oscillating spark passing 

 between two knobs, using both great electromotive force and 

 great quantity of electricity. He finds that the subsequent 

 sparks, at any rate for three hundred-thousandths of a second, 

 exactly follow every sinuosity in the path taken by the fiilot 

 spark. Thus the comparatively small resistance to the passage 

 of a second spark in air is probably due to this permanence of 

 path. 



The University Correspondence College Press has issued tlie 

 London University Guide for the year 1893-94. 



Bulletins 96-99 have been received from the Michigan 

 Agricultural Experiment Station. 



Mr. G. Gammie has prepared a report on his botanical tour 

 made on the Sikkim-Tibet frontier daring 1S92. The report is 

 issued by the Superintendent of the Royal Botanical Gardens, 

 Calcutta. 



We have received the second part of " A Dictionary of 

 Birds," by Prof. A. Newton and Dr. Gadow, extending from 

 "Ga" to "Moa." Messrs. A. and C. Black are the publishers. 



