PHYSICS, PROGRESS OF, IN 1802. 



641 



affected l>y density of illumination. He experi- 

 mented \\iih intensities varying in the ratio 

 1 : 1,000 and could have detected a change of 1 

 I..T cent. 



<% Charles II. Lees (London Royal 

 Society. Feb. 4) has found that Kundt's law that 

 metals follow the same order as regards both 

 conduction of heat and propagation of light 

 docs not hold good for crystals. He employed 

 the divided-bar method, measuring the distribu- 

 tion of temperature. The conductivity of vari- 

 ous substances in C. G. S. units was found to be 

 as follow : 



Crown plMS -0024 | Shellac -00060 



Flint Kluss '0020 Pure rubber -00088 



.It -014 



Quartz (alon? nxta) .... '080 

 Quartz (.trausveree) '016 



Paper.. '00081 



Cork -00018 



Silk and flannel -0002 



Platinum '00854 



Tin -00609 



Nickel -00500 



Electricity. Conductivity and Resistance. 

 Remold and Rucker (British Association) have 

 measured the conductivity of films of soap, glyc- 

 erin, and metallic salts. When the salts were 

 jn-e.-ent the specific conductivity was the same in 

 a film g,n/oo<i inch thick as iri a mass of the solu- 

 tion; with soap alone, however, the conductivity 

 increased with thinness to 7 times the original 

 amount. This seems due to some breaking down 

 of molecular equilibrium in the film. Ayrton 

 and Mather (" Philosophical Magazine," Febru- 

 ary) have constructed a noninductive resistance 

 of 12 platinoid strips doubled over upon them- 

 selves, with shellacked silk between the folds. 

 The inductance of the arrangement is so small 

 that it can not be measured. Dewar and Flem- 

 ing (ibid., October) have ascertained the electri- 

 cal resistance of several substances at the boiling 

 point of oxygen. The mean coefficient of change 

 of resistance between and 100 C. was found 

 to be as follow ; 



Silver -008S4 



Aluminum -00390 



Copper -00410 



Iron -00531 



At ordinary temperatures the resistance of iron 

 is 7 times that of copper, and that of nickel 10 

 times that of copper; but at the boiling point of 

 oxygen that of iron is only two thirds, and that 

 of nickel four thirds that of copper. Dr. Daw- 

 son Turner (British Association) finds that the 

 electric spark reduces the resistance of powdered 

 aluminum, copper, annealed selenium, and iron, 

 and that of small shot, but that shaking or jar- 

 ring restores the primary condition. 



Cells. Markovsky (Wiedemann's "Annalen," 

 No. 11) in experiments on gas batteries finds 

 that by adding a solution of platinum sulphate 

 the E. M. F. of an oxygen element is diminished 

 and that of a hydrogen element increased, so 

 that that of an oxygen-hydrogen element is not 

 affected. The E. M. F. is independent of change 

 of the density and temperature of t ho gas. E. F. 

 llerroun ("Philosophical Mapi/inc." June) notes 

 that though in the text-books platinum is said 

 to be negative to gold, the heat of formation of 

 auric chloride is only half that of plntinic chlo- 

 ride, which would indicate the opposite. He 

 finds that the average E. M. F. of a zinc-plati- 

 num cell is 1-5. and that of a zinc-gold cell 1-8. 

 If a gold-platinum couple be immersed in wa- 

 ter or dilute hydrochloric acid, the gold has the 

 higher potential ; in strong hydrochloric acid it 

 VOL. xxxn. 41 A 



is doubtful which is the higher; in hydro-nitro- 

 chloric acid the platinum is the higher. Prof. 

 Schuster lias constructed cells in which the elec- 

 trolyte is a gas, and finds that polarization is 

 absent with an elementary gas, but present in a 

 compound, being marked in a hydrocarbon. 

 The magnitude depends on the electrodes, being 

 small with copper and iron, large with aluminum 

 or magnesium. 



Thermo electricity. Henri Bagard (Paris 

 Academy of Sciences, Dec. 14) has made a ther- 

 mo-electric couple with zinc amalgam and a 

 solution of zinc sulphide. He finds that it is 

 absolutely constant between two given tempera- 

 tures, and varies only '0001 volt at and 100 

 when the proportion of zinc varied from -00025 

 to -00075 the mass of mercury. 



Electrolysis. L. Arons (Berlin Physical Soci- 

 ety, No. 3) finds that if a cell with sulphuric 

 acid, through which the current passes by plat- 

 inized electrodes, be halved by a partition of 

 plat ilium, gold, or silver, so that all the lines of 

 flow traverse the metal, the current is enfeebled, 

 polarization taking place on both sides of the 

 partition, while the resistance was not much al- 

 tered. He succeeded in making the partition so 

 thin that the polarization on one side quite neu- 

 tralized that on the other, and the deflection of 

 the galvanometer was unchanged. C. Ludeking 

 (" Philosophical Magazine," June) finds that the 

 decomposition of a gas by an electric current is 

 due partly to true electrolysis, partly to ther- 

 molysis, in which heat dissociates the vapor and 

 then the atoms act similarly to charged pith 

 balls. Lagrange and Hoho (Brussels Academy 

 of Sciences, Oct. 10) have observed the follow- 

 ing phenomena accompanying the electrolysis 

 of dilute sulphuric acid, the positive electrode 

 being a plate with area of 180 square centimetres 

 and the negative a wire of -25 millimetre diame- 

 ter placed half a millimetre below the surface. 

 As the E. M. F. increased a fizzing was heard 

 at the negative electrode and the liquid there 

 boiled. The phenomenon increased with the 

 difference of potential between the electrodes. 

 When this reached 16 volts and the electrodes 

 were 3 millimetres apart a number of luminous 

 points appeared between them and the surface. 

 The phenomenon took place at the same E. M. F. 

 for all electrolytes, for equal acidity. J. V'anni 

 (Wiedemann's "Annalen," No. 10) shows that 

 former results as to change in the electro-chem- 

 ical equivalent of copper with density of current 

 were due to acidity of the bath, and that the 

 deposition of copper measures currents very ex- 

 actly if care be taken to form a normal solution. 



Electro -magnetic Waves. Techer (Wiede- 

 mann's "Annalen," No. 3) finds that when a Geiss- 

 ler tube is placed between parallel wires connect- 

 ed with the condenser plates of a Hertz appa- 

 ratus, the nodal points in the tube appear dark, 

 while the other portions glow. L. Arons in- 

 closes portions of the parallel wires in a long 

 vacuum tube, which at 10 millimetres pressure 

 is filled with light and dark spaces. Prof. Kle- 

 mencic (Vienna " Berichte," Feb. 18) determines 

 electro-magnetic radiation by hanging a thermo 

 element near a fine platinum wire heated by the 

 vibration. He thus found -000155 and -000088 

 for the number of calories received per second, 

 where C. V. Boys with an air thermometer had 



