SCIENTIFIC NEWS. 



[Jan. 6, l£ 



unless, which is not hkely, it should, when almost perfect 

 in this respe' exert considerable influence on the com- 

 pass. 



The easiest method of demagnetising the separate 

 ^ieces is, after carefully examining how it is magnetised, 

 both by the compass and by iron filings, to oppose its 

 magnetism by bringing an ordinary horseshoe magnet 

 near it. A large magnet held at a few inches distance is 

 better than actually stroking the part with a magnetised 

 serving needle, as the magnetisation of the latter is more 

 liable to be altered than that of a large magnet. In some 

 complicated parts, such as a compensated balance, it is 

 necessar}^ to use a needle. Balances have been con- 

 structed by M. Paillard of two different alloys of palladium 

 having different expansive qualities. Phosphor bronze 

 is used for levers, and might be used in conjunction with 

 platinum for balances. 



The balance-wheel is the most important part, for 

 a watch provided with a non-magnetisable balance, 

 though having spring, lever, regulator arm, and escape 

 wheel of steel, will keep fairly good time after having 

 seen subjected to the influence of a powerful magnet, 

 although it has been temporarily stopped while in the 

 jTiagnetic field. 



To test a piece, such as a lever, with a compass, it is 

 -ufficient to offer first one end and then the other to the 

 aeedle, holding it at right angles (fig. 5) and at a fixed 

 distance. The needle should be attracted by either end, 

 Dut should it be magnetised, one end will attract the 

 leedle, and the other end repel it, or onlj^ attract it 

 eebly. 



Sometimes the magnetism is destroyed bj' heating 

 each part to dull redness, and re-tempering and polishing. 

 Such a method cannot be recommended, as it not only 

 jvolves considerably more labour, but is likely to do 

 .Tiore harm to the watch than a little residual mag- 

 aetism. 



It is probable that the separate parts could be com- 

 pletely demagnetised by placing them one by one in the 

 centre of a bobbin of insulated wire, like a small induc- 

 tion coil, but wound with rather thicker wire. A current 

 3hould be sent through the coil, and rapidlj' alternated 

 by means of a commutator, the strength of the current 

 oeing at the same time gradually diminished by introduc- 

 ing a resistance. The piece under treatment would 

 be magnetised first one way, and then the other, but with 

 gradually decreasing strength. This method has been 

 applied in various ways, with some success, to the de- 

 magnetisation of a watch as a whole, without taking it to 

 pieces. It has the merit of simplicity, and does not need 

 any knowledge of watch-making. The simplest way of 

 carrying it out is to spin the watch rapidly, near a 

 dynamo or powerful magnet, and withdraw it while 

 spinning. This is almost always enough to start a 

 watch which has been stopped, but its rate will pro- 

 oably remain affected. Mr. Maxim has constructed 

 in instrument for the purpose ; it consists of a magnet 

 vvhich can be rotated so as to present the north and south 

 :)oles in succession, and a holder for the watch. This 

 aolder is attached to a long screw, and during the rota- 

 tion of the magnet, the watch is gradually withdrawn 

 from its influence. A similar arrangement has been 

 used with an electro magnet, and provision is made 

 for gradually reducing the strength of the current. 

 These methods are free from the risk of injury which 

 might occur from the violent spinning, but a very 

 strong magnet would be required to destroy the effect of 



bringing a watch nearly into contact with the pole piece of 

 a dynamo, an event which may often happen while it re- 

 mains in the pocket. 



There is one other method of treating the watch as a 

 whole. It is placed on a table, face upwards, on a sheet 

 of paper with two lines crossing at right angles. The 

 dial is placed so that XII and VI are just over one line, 

 and III and IX are over the other. The deflection of the 

 compass is noted, and the watch is turned so as to bring 

 I and VII over one line, and IIII and Xover the other. The 

 deflection is again noted, and a table made for the 

 strength of the magnetism in each position. The 

 maximum and minimum, or north and south points, can 

 then be determined, and the watch is removed and passed 

 backwards and forwards in front of a strong magnet in 

 such a way as to neutralise the magnetism which has 

 thus been measured. It must then be replaced and a 

 fresh exploration made, and the process may be repeated 

 until the compass fails to detect any unusual distribution 

 of magnetism. Although good results are recorded as 

 having been effected by this means, it can hardly he ex- 

 pectod to cure effectually, unless in experienced hands, 

 and it must be a tedious operation. 



A complete protection from magnetisation is afforded 

 by an iron case. It is not necessary that it should com- 

 pletely encase the watch, but it m»ay consist merely o 

 a piece of tinned iron, bent over with the corners rounded 

 as in fig. 6. The effect is to offer an easy passage to 

 the magnetic lines of force, which will then pass round, , 

 instead of through the watch. 



UTILISATION OF FIRE DAMP. 



T T is very interesting to see fire damp, the most dreaded 

 enemy of miners, reduced by the genius of man 

 to be his agent and servant, as has been done in Ger- 

 many recently. The Wurm coal mines, near Aix-la- 

 Chapelle, are particularly noted for the amount of fire- 

 damp produced in them, and the minutest precautions 

 had to be taken to prevent dangers that, notwithstanding 

 this, were to be feared. Mr. Hilt, director of the mines, 

 undertook the work. He constructed a line of piping 

 that ran in front of all the centres of work and ended in 

 a main pipe connected at the surface with a powerful 

 suction pump. 



But it was not enough to get rid of the noxious gas, 

 it was necessary to utilize it ; and so Mr. Hilt conceived 

 the ingenious idea of causing the conduit to end in a 

 gasometer. Upon isolating the latter, and placing wire 

 gauzes here and there in the conduit, he was enabled 

 to lead the gas to the furnace of two generators and use 

 it to help to heat them. 



We are obtaining, says the Director, 30,500 cubic feet 

 of fire damp, which distil 263 cubic feet of water. On 

 uniting the fire damp of all our exploitations, we shall 

 have 64 cubic feet per minute, and shall be able to dis- 

 til 5,260 cubic feet of water per twenty-four hours. 



The utilisation of fire damp thus stored may become 

 advantageous from a commercial point of view. It may 

 serve not only for gas motors, but also, with well-con- 

 structed burners, for lighting purposes. — La Nature. 



Naphthol as an Antiseptic. — Dr. Bouchard, writing 

 in the Comptes Rendus, recommends naphthol as a power- 

 ful and relatively safe antiseptic, especially for internal 



