PHYSICS. 599 



of carbon as found to cover the inside of the tube, showing that the 

 enormous temperature reached in the explosion had decomposed the 

 carbon monoxide into its constituent elements. (Proc. Brit. Assoc. 1884, 

 688 ; J. Phys., October, 1885, II, iv, 472.) 



Sherman has investigated the fact that when a thermometer is heated 

 above a certain point the mercury column is permanently displaced 

 with regard to the scale. This point of temperature varies with the 

 glass of which the bulb is made and also with the previous use of the 

 thermometer. The range, in his experience, is between 110° and 255°, 

 the former for German and American soda-lime glass, the latter for Eng- 

 lish flint and French crystal. By much use or long heating the dis- 

 placement frequently reaches 10° and may amount to 26°. The author 

 now finds that if the thermometer be exposed to a high temperature for 

 some hours the displacement of the zero point becomes less and less 

 ■with each successive treatment, so that the curve representing the ele- 

 vation becomes more nearly parallel with the axis of abscissas, which 

 represents the hours of heating. Moreover, the thermometer after treat- 

 ment no longer shows this rise in zero i)oint on heating and is found to 

 repeat its readings accurately when exposed to similar conditions. 

 Hence the author concludes that after such treatment the thermometer 

 is as serviceable as a measurer of temperatures ranging from 0° to 300° 

 as the accustomed standard is for the range 0° to 100°. These changes 

 are accompanied by a change in the expansion-coefficient of the glass, 

 due perhaps to a partial separation of the crystalline from the amor- 

 phous constituents of the bulb glass. {Am. J. Sci., July, 1885, III, xxx, 

 42.) 



Wroblewski has compared the indications of a hydrogen thermometer 

 with those of a thermo-electric junction. The former indicates below 

 — 193° temperatures lower than the latter, thus showing a greater con- 

 traction at this temperature than the laws of Boyle and Charles require. 

 Moreover the departure increases as the temperature diminishes. The 

 hydrogen thermometer gives —207° for the temperature of solidification 

 of carbon monoxide and — 214° for that of nitrogen, while the thermo- 

 electric junction gives — 199^ and —203°. The thermo-electric curve is 

 remarkably regular, and hence it follows that the thermo electric junc- 

 tion is a more reliable indicator of temperature than the air thermometer 

 at these low points. When oxygen, nitrogen, and carbon monoxide 

 are evaporated in a vacuum the temperature falls only a few degrees 

 below — 200° {C. R., April, 1885, c, 979; Am. J. Sci., June, 1885, III, 

 XXIX, 495.) 



Mendenhall has described a differential-resistance thermometer for 

 the ready determination of temperature at a distant point. It consists 

 essentially of a thermometer of large size the stem of which has an 

 internal diameter of about a millimeter, and the bulb of which is so 

 large that a difierence of 1° gives a displacement of 5™"' in the column. 

 Running down through the stem is a platinum wii'e, about -08°"" in diam- 



