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The Stbttctube of Metals. — In a paper read 

 before the Boyal Society on May 31st last, further 

 results have been given of the investigations of 

 Professor Ewing and Mr. Bosenhain upon the 

 crystalline structure of metals. The first part of 

 the work was briefly described in these columns 

 last month. The authors have examined the 

 changes of crystalline stmirzTr which take place 

 in various metals at comparatively low tempera- 

 tures. It was noticed that a piece of sheet lead 

 when etched with dilute nitric acid exhibit? a 

 strong crystalline structure, with large crystals. 

 This was afterwards found to be due to a slow 

 process of annealing orrecrystallisatian at ordinary 

 atmospheric temperatures. The phenomenon was 

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 series of micro-photographs of certain marked areas 

 in the surface of a specimen, in order to watch the 

 change which went on through lapse of time, or 

 after application of some thermal treatment. If a 

 piece of cast lead is greatly strained by compres- 

 sion, the original large crystals, after being con- 

 siderably flattened, are driven into and through 

 one another. A piece of lead strained in this way 

 and kept for nearly six months in an ordinary 

 room, withont any special thermal treatmenT. " - 

 found to be undergoing continuous change during 

 that time. A series of photographs of this 

 specimen, taken at intervals during the six months, 

 snowed that a great number of the small crystals 

 grew larger at the expense of their neighbours. 

 In similar specimens which were kept at 200° C. 

 the growth was much more pronounced. Experi- 

 ments were also made at 100° C. and 150 : C. 

 which led to the general result that crystalline 

 growth will occur at any temperature from 

 15° C. or 20° C. up to the melting-point of 

 lead, and that in general the higher the tempera- 

 ture the more rapid is the initial rate of change. 

 A - - Hirin g feature observed in several specimens 

 was the large and rapid growth of one or two indi- 

 vidual crystals. In many instances such individuals 

 grew until they were some hundreds of times larger 

 than their neighbours. Generally the most aggres- 

 sive crystals were found near the edges of the 

 specimen. It was also noticed that a crystal which 

 had already grown considerably was at times 

 swallowed by a more powerful neighbour. Mr. 

 Rosenhain puts forward an hypothesis to explain 

 the phenomenon by suggesting that the metallic 

 impurities present in a metal play an important 

 part in the action. "When a metal solidifies from 

 the fluid state, the metallic impurities finally crystal- 

 lise as a film of what is known as eutectic alloy 

 between the metal crystals. It is thought then 

 that the observed changes of crystalline structure 

 which go on, whileSthe piece is in the solid state, 

 are accomplished by the agency of these eutectic 

 films between the crystals, in dissolving metal 

 from the surfaces of some crystals and depositing 



it on others. Several observations and experir_ 



A Revolving Magnetic Flag. — A very pretty 

 lecrure-room experiment has recently been de- 

 scribed, to demonstrate the existence of a magr, eti 

 whirl in the interior of a conductor carrying a cur- 

 rent. The conductor itself consists of a beaker of 

 mercury, the " flag ™ being a small magnet attached 

 with one end at right angles to a glass rod pivoted 

 along the axis of the beaker. The magne: is 

 fore capable of rotation in a plane at right angle- t 

 the direction of the current. A hole is bored through 

 the bottom of the beaker to admit an electrode 

 m aking contact with the mercury. The return cir- 

 cuit is afibrded by a copper vessel into which 

 beaker tightly fits, the external field due to the cur- 

 rent also being thus eliminated. The earth's mai- net- 

 ism is also neutralised by permanent magnets. 

 The glass rod is weighted to obtain neutral equi- 

 librium. Upon passing the current through, the 

 flag rotates with uniform velocity, the north-seeking 

 pole following the lines of force. 



Physical Society of London. — The final 

 mee ting for the present session of this Society was 

 held on June 22, Mr. T. H. Blakesley, vice-presi- 

 dent, occupying the chair. Dr. Barker read a 

 paper entitled " Motes on Gas Thermometry," by 

 Dr. Chappuis. The author discards hydrogen a* 

 an absolutely reliable thermometric substanc- 

 high temperatures, due to its attacking the walls 

 of glass receivers, and uses a constant volume 

 nitrogen thermometer. He obtains a value of 

 445.2° C. as boiling-point of sulphur, and criticises 

 CaUendar and Griffith's value of 444.53° C. In the 

 discussion upon the paper Professor CaUendar. 

 Mr. Glazebrook, and others took part. Professor 

 CaUendar remarked that he was unable to agree 

 with the correction to his observations suggested 

 by Dr. Chappuis. Two other papers were read,, 

 one by Professor CaUendar on behalf of Mr. H. M 

 Tory on "A Comparison of Impure Platinum 

 Thermometers," the other bv Professor S. Young;,. 

 D.Sc\. F.E.^.. on "The Law of Caffletet and 

 Mathias, and the Critical Density." The Sc ■:'. 

 then adjourned until October next. 



Induction Coil Condensers. — The discovery 

 and applications of the Bontgen rays have given 

 rise to a great increase in the manufacture and 

 sale of induction coils. The article in the " Philo- 

 sophical Magazine " for February last by Mr. K. E. 

 Johnson upon condensers in induction coils will 

 therefore be of interest . As i s well known, if a con - 

 denser is connected across the " break " in the pri- 

 mary circuit of an induction coil, the extra induced 

 current flows through it. If the maximum E.M.F. 

 in the condenser is very great, a spark occur- : 

 the break and the oscillations in the circuit are 

 diminis hed. If the capacity of the condense: 

 very large, the maxi m um condenser E.MF. is smalL 

 as is also that at the break No spark then takes 

 place. The efficiency of the coil is therefore 

 increased by increasing the capacity of the con- 

 denser, so long as the discharge by spark at the 

 break is diminis hed. When this spark is entirely 

 suppressed, the efficiency of the coil is greatest 

 and the secondary spark-length a maximnm. If 

 the condenser capacity is stfll further increased, 

 the spark-length diminish es, owing to the niaxi- 

 mnm E.M.F. in the condenser being decreased, as 

 weU as the current in the circuit. 



