616 



SCIENCE 



[N. S. Vol. XXVII. No. 694 



other resistance, and the phenomena of 

 resonance. 



The machine offers nine choices of ratio 

 of periods between the two simple waves, 

 and each of these ratios may be thrown 

 slightly "out of tune " for the purpose of 

 showing beats, or the changes in the com- 

 pound wave and the evolutions of the 

 Lissajous figure as the phase progressively 

 changes. There are three choices of wave- 

 length of the fundamental wave. The 

 amplitude of either wave may be given any 

 value between zero and the maximum per- 

 mitted by the size of the machine ; the phase 

 difference can be varied between 0° and 

 360° ; and either wave may be given any 

 desired positive or negative damping co- 

 efScient. 



Notes on Harmonic Analysis: Albert B. 



Porter. (Read by title.) 



This paper describes: (1) A geometrical 

 representation of the Fourier coefficients of 

 a periodic function as a series of solids; 

 (2) the essential mechanism of an inte- 

 grating harmonic analyzer which is based 

 on this representation; (3) a new method 

 of harmonic analysis by use of specially 

 ruled sine-coordinate paper, on which the 

 given function is plotted, and the Fourier 

 coefficients are determined by measurement 

 with an ordinary planimeter, and (4) a 

 modified form of the Yule analyzer. 



Some Experiments on the Radioactivity of 

 Potassium Salts: J. C. McLennan, Uni- 

 versity of Toronto. 



In this paper an account is given of some 

 experiments which confirm the discovery 

 by Campbell and "Wood that potassium 

 salts emit a radiation of high penetrating 

 power. 



In the first series of measurements some 

 chemically pure potassium sulphate was 

 spread into a thin layer and placed close 

 to and beneath an ionizing chamber 40 em. 

 long, 26 em. wide and 28 cm. high. The 



bottom of this vessel was closed with a fine- 

 meshed gauze which permitted the radia- 

 tion to pass through. The saturation cur- 

 rents were measured with a quadrant elec- 

 trometer. 



In the first set of measurements different 

 areas of the salt were exposed, and it was 

 found that the radiation emitted was di- 

 rectly proportional to the free surface of 

 the salt. 



In a second series of measurements a 

 layer of the salt 35 cm. by 18 cm. was 

 placed under the ionizing chamber, and 

 then gradually lowered, thus altering the 

 air column traversed by the radiation be- 

 fore it entered the chamber. The results 

 of this experiment show that it was neces- 

 sary to lower the layer of salt some 17.5 

 cm. before the saturation current was re- 

 duced one half. With the salt at a dis- 

 tance of 42 cm. from the chamber, the 

 ionization current was still approximately 

 considerable, being one tenth of its highest 

 value. In a third series of measurements 

 a layer of the salt was again placed beneath 

 the ionization chamber, and the absorption 

 of its radiation studied by covering it suc- 

 cessively with an increasing number of 

 sheets of tin-foil, and at the same time 

 measuring the corresponding saturation 

 currents. The tin-foil used in these meas- 

 urements was .0089 mm. in thickness. It 

 was found that the saturation current 

 diminished from 188 to 10 units as the 

 ntimber of sheets of tin-foil were increased 

 from to 32. Seven sheets reduced it to 

 one half its value. 



The fourth series of measurements was 

 made with the object of ascertaining 

 whether this radiation from potassium 

 salts, which from its characteristics evi- 

 dently consisted of /? or y rays, was due to 

 some property possessed by the salt in- 

 trinsically, or Avhether it was due to a 

 secondary radiation excited in the salt by 

 the penetrating rays from the earth. 



