SCIENTIFIC NEWS. 



[Jan. 6, 1 8 



THE EIFFEL TOWER. 



PROBABLY the most conspicuous object at the Exhi- 

 bition to be opened in Paris next year will be the 

 iron tower now being constructed by M. Eiffel. It will 

 be no less than i,ooo feet high, or about two and a half 

 times the height of our St. Paul's Cathedral. Visitors 

 will be conveyed to the top by means of lifts, and from 

 this great elevation there will be a splendid bird's-eye 

 view of Paris and of the Exhibition. It is also proposed to 

 estabhsh a meteorological observatory at the top of the 

 tower, and this cannot fail to be of scientific interest. 



At first a site was chosen near the railway which 

 separates the Champ de Mars from the square belong- 

 ing to the municipality. This site was a very suitable 

 one, but owing to objections raised by the authorities it 

 became necessary to select another, where the nature of 

 the soil has rendered the engineering difficulties some- 

 what greater. The foundations to receive the iron tower 

 consist of four masonry piers, and two of these are built 

 on hard gravel resting upon clay, whilst the other two 

 piers occur where there is alluvial soil resting upon 

 gravel, and this has necessitated much thicker beds of 

 concrete under the masonry. 



Each of the piers is a massive pyramid, vertical in 

 front and inclined at the back, the upper surface on 

 which the superstructure is built being inclined at an 

 angle of 45 deg., as shown in the accompanying illustra- 

 tion — taken from a recent number of La Nature. 



We need not trouble our readers with the technical 

 details of the iron structure, especially' as they are rather 

 complicated. We may, however, mention that concave 

 steel castings, weighing about five and a half tons, are 

 fixed to each pier, for the purpose of receiving the bases 

 of the iron columns. As these inclined columns grew in 

 length, they were bound together by ties and lattice 

 work, three of them being supported by staging, while the 

 fourth was kept in position by the ties of the others pre- 

 viously fixed. A height of about 1 70 feet has already been 

 attained, and the four columns are being joined together, 

 and on this the first platform will be erected. During 

 the progress of the work a temporary bracket is attached 

 to the iron framework, and on this a crane is worked, as 

 shown in our sketch, the crane being moved upwards as 

 required by means of a long screw, and then reclamped 

 to the ironwork. The girders which unite the four 

 columns at the first landing each weigh about 69 tons, and 

 M. Eiffel hopes to have this portion of the work com- 

 pleted earlj' in Januarj'. 



THE DEMAGNETISING OF WATCHES. 



LONG before the days of dynamos, watches were in- 

 juriously affected by bringing them too close to 

 powerful magnets,but it is not till lately that there has been 

 real need for non-magnetisable watches, or for suitable 

 protective cases. An American dynamo was exhibited 

 not long ago, near which was a notice warning visitors 

 that their watches might be injured if they approached 

 too close to the machine ; the inventor being apparently 

 unaware that he was thus condemning the design, rather 

 than extolling the strength of his magnets. 



The effect of magnetisation is nearly always to retard 



or to stop a watch, though the reverse is possible. It 



should be observed that simple increase of friction will 



lot make it go appreciablj' slower, but will merely de- 



■ease the swing of the balance wheel. The parts likely 



to be affected are the quickly-moving steel parts, or the 

 stationary parts in close proximity to them. The hair- 

 spring sometimes actually sticks together, partly owing 

 to the influence of some more massive part in its 

 neighbourhood. Palladium is used with success for 

 hair-springs. It is a metal rather heavier than steel, 

 and has the advantage of resisting corrosion. It is used 

 both in its pure state and as an alloy ; the resilience is 

 not so high as steel, but it is quite sufficient for the 

 purpose. Glass has been used, but the mechanical 

 difficulties of fastening it in its place, and its liability 

 to be broken by comparatively slight shock, have 

 prevented its extended use. As a spring, however, 

 it offers so great advantages that the method of manu- 

 facture may be worth describing. 



A thin metal cone (fig. 1) is mounted on a spindle, 

 placed at an inclination, the broad end of the cone being 

 open. A thread of glass is then drawn out to the re- 

 quired size, one end is attached to the top of the cone, 

 the rod from which it is made being left hanging at 

 the other extremity. The cone is brought to nearly a 

 red-heat, by directing the flame from a blowpipe to its 

 interior. The spindle is then slowly revolved, the thread 

 of glass being softened at the point of contact with the 

 cone, coiled into a conical spiral. When cool it is re- 

 moved and pressed flat against a metal plate, on which 

 the coils of the spring can be arranged evenly (as shown 

 in fig. 2). The plate is then heated until the glass is 

 again softened, and on cooling it retains the shape of an 

 ordinary hair-spring. 



The balance-wheel is the part which is most liable to 

 stop a watch by magnetisation. In a common watch 

 this is made of brass, and therefore gives no trouble, but 

 a compensated-balance is made of steel and brass. An 

 arm of steel carries a ring, and round this is cast or 

 shrunk a ring of brass (shown in fig. 3). A number ot 

 screws, with comparatively large heads, are set round 

 the wheel for adjusting the weight. The compound rim 

 of the two metals is sawn across in two places {a, a) 

 near the arm. The reason for this arrangement is, that 

 owing to the greater expansion of brass than of steel by 

 heat, the result of a rise of temperature is to curve the 

 rims inwards a little, and by thus tending to make the 

 watch go faster, to counteract the retarding effect that 

 would otherwise be produced. Regarding the steel por- 

 tion as a magnet, it will be noticed that its polarity 

 might take various forms, and the most difficult part of 

 it to demagnetise is the tip of the rim at the saw-cut. 

 A similar difficulty is met with in the regulator arm 

 (fig. 4), when this is cut through at a for the purpose of 

 giving it a spring grip. Not only is it almost impossible 

 to demagnetise it thoroughl}", but such an arm will rarely 

 be met with in which iron filings are not found bridging 

 over the saw cut. When it is remembered that an iron 

 rod held north and south, with the north end pointing 

 downwards, maj' be magnetised by a few blows with a 

 mallet, it may easily be imagined that the act of sawing 

 may be sufficient to magnetise a regulator, arm, or other 

 part of a watch. Although magnetism is present to some 

 small extent in many of the steel parts, no injurious 

 effect is, under ordinary circumstances, observable, 

 because the north and south poles lie in all directions at 

 random. 



The 'scape v.heel and the lever are important steel 

 parts, and were it not for the ruby pallets which form 

 the actus 1 bearing surfaces, a trace of magnetism would 

 have serious results. The only remaining steel portion. 



