April 27, 1S8S.] 



SCIENTIFIC NEWS. 



393 



THE COMET (li 



ON the 19th of February, Mr. Sawerthal, of the Royal 

 Observatory of the Cape of Good Hope, whilst re- 

 turning from the Photographic Observatory noticed an 

 object in the sky which looked very much like a comet, 

 and his suspicion was converted into certainty when 

 he came to examine it with a telescope. From calcula- 

 tions made by Mr. Finlay, it appears that the comet was 

 nearest the sun on the 19th of March, its distance from him 



bemg then about sixty-five millions of miles. Since its 

 - discovery the comet has been travelling in a north-easterly 

 direction, and has lately been seen in the early morning 

 in England ; it is, however, only just visible to the naked 

 eye, and is diminishing in brightness. Our illustration, 

 borrowed from the Scientific American, is from a sketch 

 made by Mr. W. R. Brookes, of the Red House Observa- 

 tory, Phelps, N. Y., on March 25th. The nucleus was 

 considerably elongated, and the tail was short and broad. 



THE EFFECT OF GAS UPON PAPER. 



HERR J. WIESNER has sent to Diitg/cr's Journal 

 a further communication upon the discoloration 

 of papers by light. He has already shown that papers 

 containing woody fibre rapidly become yellow under the 

 influence of light, owing to oxidation chiefly induced by 

 the more refrangible rays, and that wood pulp papers 

 would naturally be specially liable to discolouration. Gas 

 is less active than electric light in this respect, owing to the 

 comparative absence of actinic rays from the former. It 

 has lately been declared that gas acts prejudically upon 

 paper in other ways, and is therefore unsuitable for 

 lighting libraries ; antf Herr Wiesner has instituted care- 

 ful experiments with a view to test the truth of these 

 assertions. He had before demonstrated that a wood 

 paper after four months' exposure at a distance of 075 

 meter from an eight-candle-power gas flame, was not 

 discoloured more than by two hours' exposure to direct 

 sunlight. He, therefore, now exposed wood paper to 

 such other conditions as might be found in badly venti- 

 lated rooms lighted by gas. After an exposure of 5,400 

 hours, during which the temperature was not allowed to 

 rise beyond 21° C. (70'^ Fahr.), it was found that the 

 gases composing ordinary coal gas, whether in their 

 usual state or mixed with a fair proportion of oxygen, 

 were incapable of acting upon the paper. Strips 

 of paper were next placed in a dark-room, and in a 

 shaded position in a chamber, so badly ventilated that 

 the illuminating power of the flame was distinctly 

 diminished ; other pieces being at the same time placed 

 in a current of air in glass tubes exposed to the light of 

 the flame. After about twenty weeks, the exposed 



papers, in common with all the other contents of the 

 chamber, were covered with an equal depth of a light 

 brown sooty deposit, while those in the glass tubes were 

 unaltered. The woody paper alone had the faintest 

 5'ellow colouration, due to the action of the light. The 

 products of combustion of coal gas do not, therefore, 

 discolour or affect paper in any appreciable degree; and 

 thus it follows that gas may be freely used in libraries 

 that are properly warmed and ventilated. 



A WHEEL PUZZLE. 



SOME of our readers are doubtless aware that when 

 a wheel is travelling, the top of the wheel moves more 

 quickly than the bottom. It is an old problem, but as we 

 have recently heard it much discussed, we think a few 

 words of explanation may be welcome. To those who 

 have not already tried it, we recommend it as an amus- 

 ing exercise in geometry. 



If a wheel rotates on a fixed axis, all parts' of its cir- 

 cumference move at the same rate, but when the wheel 

 is also travelling in a horizontal direction, as in the case 

 of a carriage wheel, we have to consider not only the 



movement of the wheel about its axis, but the leffect of 

 the horizontal movement also. 



Let the circular thick line in the diagram represent 

 the wheel, and suppose that it is turning and travelling 

 in the direction indicated by the arrow. When the 

 wheel has made one-fourth of a revolution, the point A 

 at the top of the wheel will have reached A', and the 

 point B at the bottom of the wheel will have reached B'. 

 Therefore, during the same length of time, the point A' 

 on the top of the wheel must have travelled a longer dis- 

 tance than the point B on the bottom. 



The reason of this is that the horizontal motion in- 

 creases the distance A has to travel, while at the same 

 time it decreases the distance B has to travel. It is, in 

 fact, evident that were it not for this the' wheel would 

 remain in the same place, and would not get over the 

 ground at all. 



We may add that if a photograph of a moving carriage 

 wheel be examined, it will be seen that the upper spokes 

 are more blurred than the lower ones, and this is 

 simply^due to the greater speed with which the upper 

 part of the wheel travels. 



Public Lectures on Hypnotism. — According to the 

 Medical Press a committee appointed by the Academy of 

 Medicine in Belgium, to investigate and report on the 

 effects of public exhibitions of hypnotism, reports that 

 they are hurtful, physically and morally, and recom- 

 mends their prohibition. 



