348 ANNALS NEW YORK ACADEMY OF SCIENCES 



Professor Trowbridge described a new form of photometer designed for 

 the purpose of measuring the rate of decay of luminosity of a phosphores- 

 cent gas. The photometer consists of a track 3.5 meters long, made of 

 two brass rods under tension. On the track an electrically controlled car- 

 riage runs which carries the standard light. The standard light can be 

 moved away from a screen placed close to a tube containing the phos- 

 phorescent gas to points A, B, C, etc. The illumination on the screen 

 from the standard light is thus directly compared with the luminosity of 

 the gas, and comparisons are made at A, B, C, etc., as the gas fades. Seven 

 readings can be made within ten seconds, giving a variation of from | to 

 -^ the original intensity of the phosphorescent gas. The entire apparatus 

 is operated electrically, time being registered on a chromograph. 



By means of this photometer the law of the rate of decay of phosphor- 

 escence for gases has been found. In this case, for air at about 0.1 milli- 

 meter gas pressure, the expression is the same as that for the decay of 

 phosphorescent solids, or 



7=_i . 



Plotting the reciprocal of the square roots of the intensities, in the case of 

 one decay of luminous gas, with the corresponding times gives a perfectly 

 straight line. An application of the law to the grading of the light of a 

 body of phosphorescent gas as great in size as a meteor train shov/s that 

 the light of the self-luminous meteor train can be explained on the assump- 

 tion that it is a gas phosphorescence, although the train may be visible for 

 thirty minutes. A certain brightening of the sky around the radiant point 

 at the time of meteor showers which has been called the "auroral light" is 

 also explained by the application of the same law. In the latter case it is 

 evident that the feeble phosphorescing of many trains has combined to 

 give a pale glow in the regions of the heavens through w^hich the shower 

 was taking place. 



Professor Campbell briefly described the instruments used, methods of 

 standardization and application. The temperature readings obtained at 

 the blast furnace were: Metal, 1375° to 1250° C; slag, 1425° to 1375°. 

 At the Bessemer converter, 1600° C, very hot blow; 1500° C. cool. Aver- 

 age blows 1550° C. The steel was cast at 1500° to 1460° C. At the Open 

 Hearth the furnace temperatures varied from 1550° to 1705° C, the sur- 

 face of the bath being 1705°. The steel was cast at 1540° to 1460° C. The 

 temperatures of the gas producers varied greatly, one set averaging 650° C, 

 another over 850° C. The most important readings were taken at the 

 Rail Mill, on the finishing temperatures of steel rails. The readings with 

 the Fery pyrometer varied from 1000° to 1070° C, whilst the Wanner 

 averaged 1100° C. 



