534 



SCIENCE 



[N. S. Vol. XXV. No. 640 



from one end. These particular eases were 

 chosen because, besides being typical, they 

 have some interest in connection with 

 Young's and Krigar-Menzal's observations 

 on the absence or dominance of certain 

 overtones when a string is bowed at or near 

 one of their nodes. 



The Motion of a Violin String under 

 Light Bowing: Harvey N. Davis. 

 This paper discusses the influence which 

 the pressure of the bow upon the string 

 has on the resulting vibration form. For 

 each bowing speed there is, for compara- 

 tively great pressure, a considerable range 

 within which the only effect of a change in 

 the pressure is a slight corresponding 

 change in the position of equilibrium about 

 which the string vibrates, the vibration 

 form being alwaj^s that described by Helm- 

 holtz and others, h^a. the amplitude re- 

 maining the same. For smaller pressures 

 both the amplitude and the vibration form 

 change with the pressure. In particular, 

 if the pressure is below a certain critical 

 value, determined partly by the materials 

 and condition of the apparatus and partly 

 by the bowing speed, no vibrations can be 

 maintained. For pressures slightly greater 

 than this critical pressure there are no 

 overtones, the time graph of the displace- 

 ment of the point under the bow being the 

 sine curve tangent at its point of greatest 

 slope to a line representing the speed of the 

 bow. As the pressure is increased beyond 

 this value, the bowing speed remaining con- 

 stant, the mode of vibration goes over con- 

 tinuously into the Helmholtzian form. 



On Distributions of Nuclei and Ions in 



Dust- free Air: Carl Barus. 



I have recently found it desirable to 

 gather my data together for comparison. 

 There is, in fact, a serious discrepancy be- 

 tween Mr. C. T. E. Wilson's results and 

 mine when reduced to the same scale. Mr. 



Wilson 's supersaturations for negative ions 

 and cloud are distinctly higher, which cer- 

 tainly can not mean that my fog chamber 

 is in these regions inferior to his own. 

 Thus in moderately ionized dust-free air 

 my condensations begin at a drop of about 

 18.5 cm. from 76 cm. as compared with 20.5 

 in Wilson's apparatus; similarly my fogs 

 begin at the drop 20.3, Wilson's at 27.7. 

 Furthermore, at low ionization even the 

 vapor nuclei of dust-free wet air become 

 efficient in the presence of ions. It seems 

 impossible, therefore, that any positive ions 

 should fail of capture. The question is to 

 be asked why I catch the negative ions, etc., 

 at an apparently much lower supersatura- 

 tion than C. T. R. Wilson. I have enter- 

 tained doubts whether the inertia of the 

 piston in his apparatus is initially quite 

 negligible; whether in any apparatus the 

 computed adiabatic temperatures were ac- 

 tually reached. Nobody has proved it, and 

 the case is worse for tubes. Moreover, in 

 every apparatus there must be a limit at 

 which the smaller nuclei of a graded system 

 can no longer be caught in the presence of 

 the larger nuclei. But I do not believe 

 that the real discrepancy will be found in 

 any of these misgivings. It seems to me 

 to be inherent in this; in Wilson's appa- 

 ratus the results are given from the ob- 

 served volume ratio v^/v of adiabatic ex- 

 pansion; in my method the results follow 

 from the observed pressure ratio p/Pi. It 

 seems questionable whether the customary 

 constants by which one passes from one 

 group of data to the other are really ap- 

 plicable, to wet air at very low tempera- 

 tures. Moreover, when the exhaust cock in 

 my apparatus is opened for 

 < = .25 .5 1 2.5 5 m sec. 



The isothermal pressures of the fog cham- 

 ber (caet. par.) read 



p,= (57.8) 53.2 52.7 52.0 51.5 50.9 50.4 cm., 



