PHYSICS. 337 



not occur if it were practically possible to have the axis of the wire 

 pass accurately througii the center of mass of the vibrator. Another 

 error arises from the fact that in a wire recently suspended the tor- 

 sional vibration period is always slightly greater than when the 

 wire has been long used and frequently oscillated (Phil. Mag., Novem- 

 ber, 1886, V, XXII, 414; Nature, July, 1886, xxxiv, 283.) 



Barns and Stroubal have contiuued in the laboratory of the U. S. 

 Geological Survey their researches upon the effect of temper upon the 

 structure of glass and steel, and have published: "A note on the 

 structure of tempered steel," "Strain effect of sudden cooling exhibited 

 by glass and steel" (two papers), "Note on the hydroelectric effect of 

 temper in case of steel," and on "The viscosity of steel audits rela- 

 tions to temper." (Am. J. Sci., May, June, 1836, III, xxr, 380, 439; 

 September, October, December, 188G, III, xxxii, 181, 276, 444.) 



Lehmann has observed certain remarkable spontaneous changes of 

 form in solid crystalline bodies, produced evidently by their interior 

 forces. These changes were observed with the microscope and in the 

 followiug substances : Quiiiohydrodicarbouic ether, protocatechic acid, 

 and ammonium chloride. The fi'st of these substances, for example, 

 dissolved by the aid of heat, in aniline thickened with a little resin, 

 crystallized in leaflets which are parallelograms of 44°. But on grad- 

 ually lowering the temperature, these crystals change into others hav- 

 ing a pale green color and angles of OQo. This change may commence 

 at different points in the same crystal even, and so twist them, the 

 movement at the ends of the crystal having force enough to dis- 

 place the entire mass. The other bodies mentioned show the same 

 property. (Wied. Ann., xxv, 173; J. Phys., November, 1886, II, v, 479.) 



Fonque and Levy have experimented to determine the velocity with 

 wljich vibrations are propagated through the ground. In their pre- 

 liminary experiments the vibration was produced by the fall of a steam- 

 hammer of 100 tons, at the Creusot works. The transmitted vibrations 

 were observed by means of a mercury surface; their arrival, as well as 

 the instant of fall, electrically transmitted, being registered by hand on 

 a revolving cylinder. At 1,200 meters distance the jar produced by the 

 blow ceases to be perceptible directly to the senses but is distinctly 

 seen in the mercury. In the permian sandstone of Creusot, a velocity 

 of 1,200 meters per second was recorded, in a direction parallel to the 

 strata and 1,050 meters at right angles to their direction. The dura- 

 tion of the disturbance was nearly a second. At Meudon, where the 

 terrace is formed of a thick layer of Fontainebleau sand, the propaga- 

 tion of the vibration is much less rapid, 320 to 360 meters only per 

 second. But the duration of the disturbance was much longer, being 

 about 5 seconds at 500 meters and 3^ seconds at 250 meters. Subse- 

 quently tlie authors employed an apparatus constructed by Breguet, in 

 which a sensitive gelatino bromide plate was made to turn about a beam 

 of light reflected from the mercury bath. A shutter opens automati- 

 H. Mis. GOO 22 



