568 



PHYSICS, PROGRESS OP, IN 1900. 



expansion the higher the temperature coefficient 

 (except with gold) ; and that lowering the tem- 

 perature raises the limits of elasticity. The re- 

 sults agree well with those of other experimenters. 



Impact. Vincent (Cambridge Philosophical So- 

 ciety, Aug. 13) finds that when nondeformable 

 spheres impinge on plane surfaces of lead, paraffin, 

 brass, or cast iron with not too great velocity 

 the square of the diameter of the dent is propor- 

 tional to the velocity. For spheres of the same 

 material and equal velocity the diameter of the 

 dent is proportional to the diameter of the sphere. 

 The volume of the dent is proportional to the 

 energy of motion of the sphere just before impact. 

 For steady loads the square of the diameter of 

 the dent is proportional to the load. The time of 

 impact is directly proportional to the diameter of 

 the ball, other things being equal. 



Liquids and Gases. Solution. Nernst (Got- 

 tingen Academy of Sciences, 1, 1900) believes that 

 the validity of the hydrate theory of solution can 

 not be ascertained by study of osmotic pressure 

 or of any other static phenomenon, but only by 

 dynamic phenomena, such as the movement of a 

 third added substance on diffusion or electrolysis. 

 Results of experiments on these lines indicate that 

 hydration in a solution is either entirely absent or 

 takes place only to a limited extent. Rothmund 

 (Zeitschrift fiir physikalische Chemie, May 18) 

 deduces from experiment that the decreased solu- 

 bility of nonelectrolytes caused by the addition to 

 the water of various salts is due not to a reaction 

 between the substance and the dissolved salt 

 which would be accompanied by some heat effect 

 but to some action of the salt on the water. 

 Zsigmondy (Zeitschrift fiir physikalische Chemie, 

 April 3) opposes the conclusion arrived at by 

 Stoeckl and Vanino, that the so-called colloidal 

 solutions of metals are merely suspensions. He 

 regards them as real solutions, since they exhibit 

 the peculiarities of such solutions, namely, some 

 osmotic pressure and power of diffusion, concen- 

 tration without apparent change, separation when 

 the solvent freezes, and impossibility of separa- 

 tion. That colloidal gold solutions give a diffusely 

 reflected light which is elliptically polarized, are 

 precipitated by animal charcoal, and behave 

 toward the electric current like suspensions, is not 

 regarded by the author as conclusive proof that 

 they are suspensions. Schaum (Physikalische 

 Xeitschrift, 1, 1899) lias investigated the motion of 

 substances while dissolving, analogous to the well- 

 known motion .of camphor in water. The sub- 

 stances dealt with are mostly salts readily soluble 

 in water and dilute acids. The motion is always 

 greater in dilute acid than in water, and its nature 

 is characteristic. The crystal generally moves at 

 first in a zigzag, then changes to a curve, and finally 

 rotates rapidly. The rate of motion depends on 

 the rate of solution. (See also Double Kcfraiiiim, 

 under LIGHT.) 



Surface Tension; Films. Hall (Dublin Royal 

 Society, 9, 1899) shows that the liquor from the 

 settling of the froth of a soap is stronger in soap 

 than the original solution. There must be a con- 

 centration of soapy matter after the formation of 

 ! film, which agrees with Rayleigh's investigations 

 of the stability of soap bubbles. Donnau (Zeit- 

 schrift fiir physikalische Chemie, Dec. 22, 1899), 

 from experiments on soap emulsions, after com- 

 parison with the results of Krafft on the boiling 

 points of soap solutions with those of Rayleigh 

 on the formation of froth on liquids, and with 

 Hall's observation just mentioned, concludes that 

 surface concentration causes a considerable dimi- 

 nution in the amount of work necessary to in- 

 crease the surface of separation of an oil and alkali 



solution, and that it is to this that the formation 

 of small bubbles is due. Malagoli (Nuovo Ci- 

 mento, May) produces durable films on skeleton 

 figures by dissolving 40 grammes of gelatin and 

 10 grammes of soap in 500 of water at a tempera- 

 ture not exceeding 80 C. The films are obtained 

 by dipping the skeletons into the solution and 

 drying for twelve hours. They are not thin enough 

 to show interference colors. Vincent (Journal de 

 Physique, February) believes that a thin film of 

 silver on glass is bounded on both sides by what 

 he calls " transition superficial layers," of a differ- 

 ent constitution from the rest of the metal. These 

 in the case of silver are of smaller conductivity 

 and the joint thickness of the two is about 

 50 X 10~ 7 centimetres. Quincke (Annalen der 

 Physik, June) combats this idea, and attributes the 

 observed variation of resistance to a variation of 

 density. This author believes that in all cases 

 wedges of solid material are to be preferred to 

 liquid films for the determination of molecular 

 forces. 



Condensation. Barus (Science, Feb. 9) believes 

 that condensation is due always to nuclei pri- 

 marily, and that whether these are ionized or not 

 is of secondary importance. There is no note- 

 worthy difference between the action of air car- 

 rying such dust and that of ionized air. 



Air Resistance. Bryan (Nature, Nov. 30, 1899) 

 describes recent researches of Le Dantec and of 

 Canovetti on this subject. Le Dantec makes the 

 surface under test slide down a vertical wire. 

 The start releases an electric recording device. 

 and the current is broken when the body strikes 

 the buffer at the end of its descent, which occu- 

 pies 1, 2, or 3 seconds. A surface 1 metre square 

 at a velocity of 1 metre per second experience-- a 

 resistance of 81 grammes. The form of the plate 

 is of importance, and the resistance appears to !>< 

 proportional to the length of the contour. Tlie 

 law that within certain limits the resistance is 

 proportional to the square of the velocity i-= 

 verified. 



Canovetti suspends his bodies from a wire 370 

 metres in length, stretched along the slope of a 

 hill. The resistance was found to be 90 grammes 

 (instead of Le Dantec's 81). He also tried bodies 

 of the shape of a Challais balloon a long cone 

 and a hemisphere joined by their bases, enveloped 

 in a net; the resistance was 80 grammes, and 

 largely due to the net. 



Gaseous Viscosity. Jilger (Vienna Academy 

 Sitzungsberichte. January March) finds that the 

 path over which a molecule carries a definite 

 amount of momentum exceeds its mean free path 

 by the diameter of a molecule at most, and i- 

 only one half this on the average. As the via 

 cosity is proportional to this path, it is also a 

 function of molecular diameter, and when this lie 

 comes very large the viscosity approximates to 

 infinity. The author shows this more exactly l>y 

 formulae. 



l\.r)>lox\re Waves. Le Chatelier (Comptes Ren- 

 dus, June 25) shows by photographic method- 

 that in various explosive mixtures ignited l>\ an 

 electric spark the speed of propagation of the 

 flame at once assumes a value of several hundred 

 metres a second, and rapidly increases to beyond 

 1.000. Shortly after the appearance of the flame 

 the explosive wave, with a greater and uniform 

 velocity, is suddenly formed. The distance- 

 traveled by the flame before the formation of the 

 explosive wave vary from 1 decimetre to 1 metn 

 The greatest observed velocity of the explo-jvc 

 wave was 2.920 metres per second. Yieille 

 i Comptes Rendns. Dec. :><>. 1890) finds that 

 plosives are not necessary to produce wave- 



