January, igo6.] 



KNOWLEDGE & SCIENTIFIC NEWvS. 



331 



angles to the general direction of the main tail. Such peculiari- 

 ties are quite contrary to the effect produced by the sun. In 

 many cases it would seem that this emissive power is great 

 enough to entirely overcome the direct pressure of the sun's 

 light. Not only this, but the sun's light appears to have no 

 bending effect towards the radius vector, as might be ex- 

 pected. Third, an outside influence quite apart from the 

 comet, which is shown by the many rapid distortions and 

 deflections of the tail. There appears to be clear evidence 

 that this is some sort of resistance offered by a kind of 

 medium not uniformly distributed in the planetary spaces, as, 

 for instance, a meteor swarm. Encounters with such a 

 medium would readily explain the sudden brightening up of 

 some comets when long past their theoretical maxima, as was 

 shown by Sawerthal's comet in May, 1S88, or it might account 

 for the breaking up of such a comet as Biele's. It would 

 seem that something of this nature was chiefly instrumental in 

 producing the special peculiarities of the tail of Brook's comet 

 in October and November, iSgj. Photographs taken by 

 Barnard on November 3 and 3 show most remarkable 

 changes, and these are strikingly shown in a composite picture 

 madeby superposing the two plates star for star, giving the two 

 positions of the comet with 24 hours' interval. There is a 

 difference of nearly 15 between the directions of the tail in 

 the two cases, while it is remarkable that the position of the 

 ends of the tails do not appear to have materially changed, 

 and various portions are seen to be detached from the main 

 stream. 



Basing on these evidences of quick change a suggestion 

 that every active comet should be photographed as often as 

 possible, he points out that this might with advantage be done 

 hour by hour during every night, as by this means the actual 

 changes in any part of the cometary matter might be followed 

 with certainty, and it may be possible to determine the exact 

 value of the motions of the particles in the tails of various 

 comets, or the same comet, at different distances from the 

 sun, and so give the true law of the velocities of these particles 

 apart from any theory. It seems then more likely that the 

 difl'erent tails of a comet are all made up of the same kind of 

 particles, and the cause of their different directions is that 

 they are ejected towards different parts of space by a force 

 residing in the comet itself. The evidence of the spectroscope, 

 so far as it goes, has certainly not shown them to be of very 

 diverse elements. 



CHEMICAL. 



By C. .AiNswoKTH Mitchell, B.A. (Oxon.), F.I.C. 



Acetylene Bla^ck. 



The old method of obtaining a black pigment for printing mk 

 was to conduct the smoke from burning wood, oil, or resinous 

 substances into a cylindrical chamber in which were hung 

 sheep skins or sacking. An inverted iron cone was suspended 

 from the top of the chamber, which it fitted so exactly that 

 when lowered its edges scraped the suspended sacking and 

 removed the black deposit. There arc numerous other 

 methods based on the same principle, such as, for instance, 

 that claimed in a recent U.S..\. patent, in which sevi-ral 

 oil lamps are burnt beneath a IioIIdw cylinder through which 

 passes a current of cold water, the deposit of lampblack being 

 removed by a fixed brush as the cylinder revolves. However 

 carefully prepared, lampblack invariably contains more or less 

 tarry oil, which being yellow detracts from the depth of tone, 

 and the usual method of removing this is to calcine the 

 black in closed iron boxes with only a small opening for the 

 escape of impurities, every precaution being taken to prevent 

 the admission of air. The discovery of natural gas in various 

 parts of the L'nited St.ites put a cheap source of bl.ack at the 

 disposal of the maker of printing ink, and led to the .\nieri- 

 can inks acquiring a high reputation for depth and richness of 

 tone. The gas issues from borings 2000 feet in depth, and is 

 burned in jets beneath revolving iron rings, on the surface of 

 which the black is deposited, about 1000 cubic feet of gas 

 being cousumed in the production of i lb. of gas-black. The 



product is much purer than ordinary lampblack, and in the 

 crude state contains 92 to 93 per cent, of carbon, 5 to 6 per 

 cent, of oxygen, i to 2 per cent, of hydrogen, and traces of 

 mineral matter. Its tinctorial power is also much higher, and 

 it requires less purification than lampblack. A still purer and 

 more intense black has recently been prepared by Ur. Frank 

 by exploding a mixture of acetj'lene with carbon monoxide or 

 dioxide, and it is claimed that this product is superior to the 

 best American gas-blacks both in quality and covering power. 

 On the other hand, its cost is likely to be greater than the 

 American blacks, which at the present time fetch about 3d. or 

 4d. a pound. 



Water from the Simplon Tunnel. 



In the course of the construction of the Simplon Tunnel 

 numerous springs were encountered, and the water from one 

 of these, about five miles from the Italian end of the tunnel, 

 has been analysed by Mr. .\. G. Levy. The water, which had 

 a temperature of 113' F. at the point of collection, was clear, 

 colourless, and without smell, but had a saline taste. It con- 

 tained 106-5 grains of solid matter per gallon (about five times 

 that of London drinking water), consisting principally of cal- 

 cium sulphate, with a considerable proportion of magnesium 

 sulphate, and small amounts of other salts. It was quite free 

 from organic matter and also from chlorine, which latter fact 

 was the remarkable characteristic of the water ; since, con- 

 sidering the distance it must have travelled underground to 

 attain its high temperature, one would have expected it to 

 come in contact with soluble chlorides somewhere on its way. 



Photo-Active Properties of Rabbits' Blood. 



Experiments have been made by Dr. V. Schlapfer, of the 

 Pathological Institute of Zurich, to determine whether blood 

 is capable of affecting a photographic plate in the dark. For 

 this purpose the fresh blood of albinotic and pigmented 

 rabbits was employed, with and without previous exposure to 

 light, and also after treatment with prussic acid and potassium 

 chlorate. In each case the plate was covered with black 

 paper, on which was placed a photo-neutral capsule of paraffin 

 wax containing the blood. It was found that the blood of 

 pigmented rabbits had a very much weaker effect upon the 

 plate than that of albinotic animals. The activity of both 

 disappeared after some days, but could be restored again by 

 exposure to light. Blood treated with prussic acid was in- 

 variably inactive, whereas that of animals poisoned with 

 potassium chlorate was always active. The slinu'lative influ- 

 ence of light upon the photo-activity of the blood has sug- 

 gested to Dr. Schlapfer a theory to account for the marked 

 difference in the behaviour of the blood from the pigmented 

 and the albinotic rabbits. He considers it possible that in 

 the case of the albino the blood circulating in the cutis may 

 be acted upon to a considerable extent by the light and thus 

 rendered photo-active, whereas the pigments in the skin of the 

 brown rabbit may act as a light-screen and weaken the effect 

 of the rays. 



GEOLOGICAL. 



By Edwaku .\. Makti.n, F.G.S. 



A Twin-Earthquake. 



Dr. Cuaklls Davison keeps unceasing watch over the various 

 earthquake shocks which are constantly visiting our islands, 

 more frequently perhaps than most people believe. In a 

 recent paper he has described the Doncaster earthquake of 

 .•^pril of this year. He tells us that it was a twin-earthquake, 

 with its principal epicentre half-a-mile north of Bawtry. and 

 the other about four miles east of Crowle, close to the centre 

 of the Ilcssle disturbance of .Vpril, 1902. Last .\pril the 

 earthciuake-area included about 17,000 square miles. He says 

 that a twin-earthquake is probably due to the difl'erontial 

 growth of a crust-fold along a fault which intersects it trans- 

 versely, the first movement as a rule being one of rotation of 

 the middle limb, accompanied by the almost simultaneous 

 slip of the two arches, and followed soon afterwards by a shift 

 of the middle limb. 



