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SCIENCE. 



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tions of potassium hydroxide, hydrochloric, 

 nitric and sulphuric acid, and ammonium 

 chloride, potassium chloride, aluminum and 

 potassium sulphate. A primary cell com- 

 posed of aluminum, potassium sulphate, 

 aluminrun and carbon, was also investi- 

 gated. The peculiarity of this cell was 

 that it gradually increased to a maximum 

 and again fell to its normal value when 

 disturbed. It was also shown that the 

 amount of current that could be taken from 

 the cell -was very small, and that the tem- 

 perature coefficient was positive. 



On the Differential Telephone: William 

 DuANE, University of Colorado. 

 Two separate coils are wound on the 

 bobbin of a telephone receiver, and by suit- 

 able means are adjusted so as to have equal 

 resistance, and equal self-induetances, and 

 so that the magnetizing effect of a current 

 flowing through one coil would be annulled 

 by that of an equal current flowing in the 

 proper direction through the other coil. 

 To measure a self -inductance the unknown 

 coil X and a variable self-inductance stand- 

 ard S are placed in series with the two 

 , receiver coils respectively, and a non-in- 

 ductive resistance box B is inserted in series 

 with S or X, according as the resistance of 

 X is greater or less than that of S. The 

 two entire circuits are joined in parallel, 

 and an alternating E.M.P. is applied to 

 the branch points. Values for B and S 

 can be found easily, such that no sound is 

 heard in the receiver, and, when this is the 

 case, the self-inductance of S equals that 

 of the unknown coil X. The magnetizing 

 effects of the two receiver coils can be equal- 

 ized by placing a small auxiliary coil in 

 series with one of the receiver coils and with 

 its plane parallel to the axis of the receiver. 

 Joining the two receiver coils in series and 

 sending an alternating current through 

 them, a position for the auxiliary coil can 

 be found that completely extinguishes the 



sound. With a receiver that will detect 

 10"" amperes, the theoretical accuracy is 

 about one one-hundredth per cent. Prac- 

 tically an accuracy of one part in five thou- 

 sand is not difficult, as absolute silence can 

 be obtained, if there is no iron in coil X. 

 The advantages of this method of measur- 

 ing self -inductance are: (a) That the appa- 

 ratus is portable and does not get out of 

 order easily; (&) that great accuracy can 

 be obtained and the manipulation is not 

 difficult; (c) that only one standard is re- 

 quired, and it is not necessary to know the 

 value of any resistance or bridge-wire 

 lengths. The disadvantage is that the self- 

 inductance of the standard must equal that 

 of the unknown coil. A range from zero 

 to 150 milli-henrys can be obtained, how- 

 ever, Avith ordinary laboratory apparatus. 



The Selective Beflection of Fuchsin: W. B. 



Cartmel, University of Cincinnati, 



Presented by D. B. Brace. 



This investigation was undertaken in 

 order to ascertain whether the reflection 

 from substances showing metallic reflection 

 agreed with the values computed from re- 

 flection formulas. The reflection from a 

 fllm of fuchsin was determined for various 

 wave-lengths. The films of fuchsin were 

 deposited upon a glass plate, and the re- 

 flection was measured not only from the 

 upper surface of the fuchsin, but also 

 from the interface between the fuchsin and 

 the glass. The measurements were made 

 by means of a Brace spectro-photometer. 

 Instead of using the usual method of com- 

 paring the light reflected from the fuchsin 

 with the light i-eflected from some other 

 substance, whose coefficient of reflection 

 was assumed to be known, the reflected 

 light was compared with the direct light 

 from the same source which supplied the 

 reflected light. The work was begun last 

 summer at the University of Nebraska and 

 is now being continued at the University of • 

 Cincinnati. 



