106 



POPULAE SCIEI^CE NEWS. 



[July, 1888. 



angles to each other, but the length of one maj' 

 be variable. In this system, instead of a 

 cube, we should have a square prism of varj'ing 

 length. Comparatively few substances crys- 

 tallize in this system, such as ferrocyanide 

 of potassium and cassiterite (tin-ore). 



In the trimetric system all the three axes of 

 the crystal are of varying length, although still 

 placed at right angles to each other. This 

 system includes a large class of substances, 

 among which may be mentioned nitrate of pot- 

 ash (saltpetre) and a great many minerals. 



The monoclinic system comprises a very 

 large number of substances, and is distin- 

 guished from the trimetric bj' having one of 

 the axes inclined at a varying angle to the 

 other two, which remain at a right angle to 

 each other. Borax, sulphate of iron (cop- 

 peras), carbonate of soda, and sulphate of 

 soda (Glauber salts) are included in this sys- 

 tem. 



In the triclinic system, of which sulphate of 

 copper (blue vitriol) is a good representative, 

 all the axes are of unequal length, and are in- 

 clined to each other at varying angles. 



The remaining system — the hexagonal, or 

 rhombohedral — differs from the others in hav- 

 ing four axes, three of which are equal, in the 

 same plane, and inclined to each other at 

 angles of C0° ; while the fourth, or principal 

 axis, is peri)cndicular to them all. The six- 

 sided prism is one of the typical forms of this 

 system, which comprises ice, (juartz, car- 

 bonate of lime, and many other important sub- 

 stances. 



As ma3- be imagined, the number of geomet- 

 rical forms which these different s^-stems may 

 give rise to is almost endless, especiall3' as 

 compound crystals, where one form is modified 

 by another, are very common ; but although 

 the crystals of the same substance may differ 

 in appearance, the systems are always dis- 

 tinct. Crystals of alum, for instance, which 

 belong to the regular system, may be modi- 

 fied by the cube or other forms of the same 

 system, but never by those of any other 

 S3'stem. It is true that a few substances, 

 lilce sulphur and carbonate of lime, crystallize 

 under different conditions in two different 

 systems ; but the form of any given crystal 

 is always true to its particular system, and no 

 mixed forms have ever been observed. 



The crystalline nature of different substances 

 varies greatly. Iodine, for instance, alwa3S 

 occurs in the crystalline form ; while silica 

 cannot be artificially crystallized at all, though 

 the beautiful crystals of quartz show that in 

 Nature's laborator}- it has been done on a large 

 scale. Bismuth readily- crystallizes when 

 melted, and allowed to cool slowly, while crys- 

 tals of gold are rarely seen. Many salts, 

 when crystallized from a solution in water, 

 take up a certain amount, which is known as 

 water of crystallization, and appears to form 

 a part of the structure of the molecule. It 

 can be driven off by heat, causing the crystal 

 to crumble into powder, but not otherwise 

 changing the nature of the substance. Carbo- 

 nate of soda, for instance, when crj'stallized, 



contains ten molecules of water, amounting 

 to about sixty-three per cent of its weight, a 

 large part of which is given off bj' exposure 

 to the air at ordinary temperatures. 



What the meaning of the crystalline form 

 is, or its relation to the chemical composition, 

 is as yet unknown. Compounds chemically 

 allied to each other generall}- crystallize in 

 the same sj-stem, although there are excep- 

 tions to this. The crystal may be an indica- 

 tion of the actual shape of the molecule, or 

 it may only be the result of the equilibrium of 

 forces developed in that molecule. Whatever 

 may be the cause of the beautiful geometrical 

 forms which all unorganized matter tends to 

 shape itself into, it is a widespread and 

 universal force which shows itself in the deli- 

 cate hoar-frost, as well as in the rocks of the 

 mighty mountain-chain. Certain geologists 

 have even tried to prove tliat our earth itself, 

 as it cooled and solidified, tended to take the 

 form of a gigantic crystal ; and it is not im- 

 possible that we maj- j-et pass the line between 

 organized and unorganized matter, and find 

 that the forces which give to the alum or salt 

 crystal its characteristic shape arc the same 

 as confer symmetry and beauty upon the grow- 

 ing plant and animal. Of course, this is only 

 speculation ; but no one can say how soon it 

 may not be a recognized scientific fact. 



[Special correspondence of the Popular Science yews-l 



BERLIN LETTER. 

 Herr W. Meissel, second officer of the North 

 German Lloyd steamer " Werra," has devised a 

 means of calming the sea by the use of oil, from on 

 board a vessel, over a greater distance than has 

 hitherto been possible. He employs rockets filled 

 with oil, which are shot off in such a way that the 

 oil itself is made to fall like rain on the troubled 

 waters, and smooth a path for the vessel. The 

 rocket consists of an oil-cylinder of tin, together 

 with a chamber filled with gunpowder. Experi- 

 ments with the invention have been very satisfac- 

 tory, demonstrating the practicability of calming a 

 surface from fifteen hundred to two thousand 

 square feet in extent. The inventor intends to 

 extend his idea, and prepare oil-bombs on the same 

 principle. 



The balloon department of the Prussian army 

 has adopted an invention which promises to facili- 

 tate aerial reconnoitring. Lieut. Richter, an ex- 

 artillery officer, and Dr. JSIajert, a young chemist, 

 have hit upon a method of producing inflating-gas 

 on the spot where it is required, whether in the 

 heart of an enemy's territory or on board a man-of- 

 war. The apparatus for developing the gas re- 

 sembles somewhat in appearance a traction engine 

 or a threshing-machine, is drawn by six horses, and 

 warranted to go wherever a field-gun can find 

 access. The lower part is a furnace, adapted for 

 any kind of fuel, especially wood, which is so 

 easily obtainable almost anywhere; and above this 

 are several parallel layers of retorts, about thirty 

 in number, into which are thrust cases or cartridges 

 filled with a mixture of zinc-dust and hydrate of 

 lime. From this mixture is developed, by the action 

 of heat, the hydrogen gas required by the balloon. 

 About two hours are needed for producing a suffi- 

 cient quantity of the gas. The authors of this 

 system maintain its superiority to all others in 

 cheapness, facility, and safety. The cases of com- 



pressed gas used by England and other countries 

 are liable to explode while being transported from 

 place to place, while the gas itself has frequently 

 proved fatal to those handling it. The experi- 

 ments conducted at Fiirstenwalde, about an hour's 

 ride by rail from Berlin, were witnessed by the in- 

 vited representatives of the principal European 

 powers (France and Uussia excepted), and proved 

 so satisfactory that the Prussian War Department 

 adopted the invention. 



Trials have recently been made near Potsdam, 

 by the War Department, with magnesium light for 

 signal-purposes, and the use of this substance for 

 the so-called lightning-flashes on lighthouses was 

 found expedient. The experiments were conducted 

 partly on level ground, partly on the North Tower, 

 situated on the Pfingstberg; and they all showed 

 the remarkable range of the light. Both the flashes 

 on the tower and those on the level ground, as well 

 as the rockets, which ascended some thousand feet, 

 were distinctly visible from all the fixed points of 

 observation; e.g., from Brandenburg, Belzig, Span- 

 dau, Charlottenburg, and Berlin, — distances of 

 thirty and thirty-five miles. 



An ingenious resident of Berlin, Capt. Plessner, 

 whose antiphon, by the way, has freed so many sen- 

 sitive nerves from the torture of inharmonious 

 music, has now taken pity on the stairs-climber, 

 and produced a cheap and simple elevator for 

 domestic purposes. It is on the principle of the 

 inclined railway, and the motive-power is furnished 

 by tlie city water, which is applied in the cellar. 

 Each flight is to have its separate chair; .-:o that, for 

 example, A can ascend from the first to the second 

 story while B is on his way from the second to 

 the third, or C is descending from the fifth to the 

 fourth. The chair, being only of the width of the 

 humali body, takes up but little room, and leaves a 

 free passage for those who prefer to walk up rather 

 than ride. It is set in motion by a simple pressure 

 upon one of its arms, while after it ha.s been used 

 it slides back to the bottom step, its descent being 

 .so regulated that it can carry a passenger with com- 

 plete safety. The invention may be more curious 

 than practical, but it is at least ingeuious. The 

 motive-power is' more or !e.ss expensive according 

 to the price of water. In Berlin the chair may be 

 used at an expense of a little over one-tenth of a 

 cent for each trip; the power, of course, remaining 

 unused when the chair is at rest. 



A Hanover physicist, Dr. Kayser, has succeeded 

 in obtaining a photograph of the aurora borealis 

 from the summit of Mount Rigi in Switzerland. 

 This is of interest because it has hitherto been 

 held impossible to photograph the aurora, no 

 plate being sensitive enough to be impressed by its 

 rays. The well-known manual of physical geog- 

 raphy by Gunther (Stuttgart, 1885) distinctly states 

 that it is "utterly impossible to photograph the 

 aurora: the most carefully prepared plate remains 

 neutral when exposed to its rays." Dr. Kayser 

 made use of especial precautions, and employed a 

 colored dry plate, the so-called azalin-trockenplalte. 



ilEDiCAi. papers bring news of the discovery of 

 the cause of that disease which is feared only less 

 than consumption, — the cerebrospinal meningitis. 

 In this age of Pasteur and bacteria we are prepared 

 to learn that one of these contagion-bearing germs 

 is responsible for tlie disease, and it has received 

 the appropriate name meningococcus. Its activity 

 consists in the inflammation of the envelop of the 

 spinal marrow and of the brain, and it is identical 

 with the cause of the inflammation of the lungs, 

 whicli latter disease so frequently accompanies the 



