PHYSICS. " <!')! 



i'ient of expansion, the value of which at JC^ was found to be 0-000Ho7 

 and at 30"^ 0-000670; (2) that india-rubber in a stretched state expands 

 to the same extent as when not stretched, no point of minimum den- 

 sity existing ; (3) that the apparently anomalous behavior of stretched 

 rubber is a case entirely analogous to that of anisotropic crystals 

 which expand differently in different directions ; Iceland spar, as Mit- 

 scherlich showed, contracting by heat in a direction i)erpendicular to 

 the principal axis, though its volume as a whole increases. Moreover, 

 when stretched, ordinary rubber becomes anisotropic and gives color 

 between two crossed Nicol prisms, the direction of the strain lying at 

 45° with the plane of polarization. {Nature, October, 1885, xxxii, 625.) 



In a subsequent note, Tomlinson agrees with Schmulewitsch that 

 the effect of heating a stretched piece of rubber is to lengthen it if the 

 tension is small, and to shorten it if the tension is large ; so that for a 

 certain tension there wiU be neither elongation nor contraction. More- 

 over, Tomlinson concludes from his experiments that the critical tension 

 will be lower the higher the temperature. ( Vierteljahrschr. Nat. Ges. 

 Zurich, XI, 202 ; Nature, November, 1885, xxxiii, 7.) 



Gernez has continued his researches upon the changes in the crystal- 

 line form of sulphur produced by heat. He finds that while the octo- 

 hedricform may be preserved at all temperatures below its fusing point, 

 yet that at 97'6o and above if touched with a fragment of prismatic 

 sulphur, it is transformed into the prismatic variety. To this state ol 

 unstable equilibrium he gives the name crystalline surheating. On the 

 other hand, the change of prismatic into octohedral sulphur with de- 

 creasing temperatures, shows a retardation analogous to that above 

 mentioned, to which the author, following Mallard, gives the name crys- 

 talline surfusion. The conditions affecting these uncertain states he has 

 now investigated, and has concluded : 1st, that the speed of devitrifi- 

 cation is not greater as the temperature is lower, there being always 

 an intermediate temperature of maximum rapidity of change; 2d, that 

 the crystalline form is not always sufficient of itself to identify the va- 

 riety, since considerable differences exist in pieces having the same 

 form ; 3d, that the action of heat upon liquid sulphur at a constant tem- 

 perature produces a change which increases with time and continues 

 even after solidification; 4th, that liquid sulphur heated from a given 

 temperature and then cooled again to the same temperature undergoes 

 a modification manifested by change of properties, which continue even 

 after solidification ; 5th, that octohedral sulphur, melted, solidified in the 

 prismatic form, and then changed to the octohedral form, has not re- 

 covered its primitive properties, and does not even after many months 

 exposure to the ordinary temperature. {J. Fhys., August, 1885, II, IV, 

 349.) 



Eaoult has continued his investigations on the action of dissolved 

 substances in lowering the freezing point of solutions. His results show, 

 1st, that if in the solution of an alkali salt containing one equivalent of 



