January 5, 1922] 



NATURE 



of two liquids. Moreover, as it has been shown that 

 two free molecules of a gas cohere (coalesce) from 

 this same cause, it is justifiable to conclude that in all 

 cases down to molecular dimensions cohesion is 

 simply a surface jorcc pulling in the periphery of the 

 contact area perpendicularly to that area. It may 

 be remarked also that these results furnish no 

 t-\idence of the so-called molecular attraction. 



By calculation this force binding two molecules of 

 water together is 205x10-' dynes; of mercury, 

 77x10-" dynes. These agree with Dr. Chatley's 

 statement that (molecular) cohesion is of the order 

 of 10- ' dynes. Again, in the case of two molecules 

 rohermg m this manner the enveloping force can have 

 range not greater than two molecular diameters, 



hile for larger molecular masses the range may be as 

 great as three or four molecular diameters. It thus 

 fulfils the condition for the range of action. In com- 

 parison with their gravitational attraction this force 

 binding two water molecules together is of the order 

 10" times as great. It is of the same order as the 

 electrical attraction of two oppositely ionised mole- 

 cules just before they come into contact. It causes 

 a pressure on the interior molecular mass of the same 

 order as the intrinsic pressure of the liquid. It does 

 appear, then, that one force can be conceived as having 

 all the properties of cohesion. 



The conception of this force as a cause of molecular 

 phenomena appears to be, in fact, fundamental. It 

 solves the problem of surface tension ; it explains, as 

 we have seen, both cohesion and adhesion, and it 

 accounts satisfactorily (Phil. Mag., ibid.) for the latent 

 heat of condensation. But besjcles all this there is 

 the remarkable coincidence that the force itself is 

 located, or performs its function, in the precise area 

 bounding free mass that the phenomena of reflection 

 and refraction of light take place and electrons have 

 their movement. These considerations give point to 

 Dr. Chatley's concluding words : " It would appear 

 that a complete solution of the macroscopic properties 

 of matter would also solve the question of the inner 

 structure of the molecules and atoms." 



Wilson Taylor. 



Physics Laboratorv. University of Toronto, 

 Canada, November 15. 



The Resonance Hypothesis of Audition. 



Additional evidence in favour of the resonance 

 hypothesis of audition has been found recently. 



The study of long-distance telephony has shown 

 that low-pitched notes travel more rapidly than do 

 those of high pitch, owing to the impedance of the 

 electrical circuits. Mixed tones must, therefore, arrive 

 with phase relationships between the high and low 

 tones quite different from those with which thev 

 started. 



In spite of this, even such complex sounds as those 

 composing human speech are found to suffer but 

 small apparent change in quality and distinctness 

 during transmission. And this statement appears to 

 apply equally to wireless telephony, where similar 

 changes of phase must occur. 



These facts suggest that the ear responds to tones 

 quite independently of their relative phases, and there- 

 fore that true harmonic analysis must take place in 

 the organ of Corti. A survey of the different types 

 of harmonic analysers used in physics, for tide pro- 

 duction and the like, shows that such harmonic 

 analysis is invariably performed bv a series of some 

 type of resonator. Presumably, therefore, since the 

 ear can carry out harmonic analysis, it also must 

 contain resonators. 



To test the premises more thoroughly the following 

 experiment was carried out : — 

 NO. 2723, VOL. 109] 



Two electrically driven tuning-forks, emitting pure 

 tones, were connected to separate battery and switch 

 circuits, and were mounted on separate tables, so that 

 while they vibrated independently their tones entered 

 the ear of the observer simultaneously. They were 

 tuned so that their tones had rates of vibration in 

 the ratio of i and 3, this ratio being chosen because 

 of all pairs of tones these give the largest changes 

 in the form of the sound wave-curve as the relative 

 phases of the tones are changed. Thus with one 

 phase relationship the sound wave-curve has a single 

 sharp, well-marked peak, whereas with another phase 

 relationship two peaks are found, having a trough 

 between them. If, then, the ear is affected at all by 

 the form of the sound wave-curve, these two tones, 

 combined in different relative phases, should show 

 it. The experiment was performed by causing the 

 higher-toned fork to sound continuously, the lower- 

 toned one being turned on and off at irregular inter- 

 vals, so that the relative phases should be chance 

 ones. No difference whatever in the quality of the 

 sound could, however, be detected by the observer. 

 The response of the ear appeared to be quite inde- 

 pendent of the relative phases of the tones, and, there- 

 fore, we must conclude that the ear effects a true 

 harmonic analysis by means of resonators. 



If the above experiment is repeated with two 

 sources of tones that are not free from overtones 

 it is found that the ear does readily detect differences 

 in the quality of the sound as the relative phases 

 of the tones are altered. For example, if Helm- 

 holtz's syren is used with, say, 18 holes operating in 

 the lower wind chest, and 6 holes in the upper, then 

 there are found to be 18 regularly spaced positions 

 where the lovyer tone predominates, and 18 inter- 

 mediate positions in which the upper tone pre- 

 dominates. 



These effects are produced by the summation and 

 interference between the upper tone and the second 

 harmonic overtone of the lower tone. When holes of 

 both wind chests are exposed simultaneously, summa- 

 tion occurs, and the upper tone predominates, whereas 

 when the holes of one chest alternate with those of 

 the other, interference occurs which weakens the upper 

 tone, so that the lower tone predominates. 



Many years ago there was considerable controversy 

 as to whether the ear could, or could not, detect 

 difference of phase. The above experiments suggest 

 that pure tone free from harmonics may have been 

 used by one school, and impure tones containing har- 

 monics by the other, because in this way their differ- 

 ence in opinion could be readily explained. 



C. R. G. CosENs. 

 H. Hartridge. 



King's College, Cambridge. 



The Action of Sunlight. 



In Nature of December 15 Sir Oliver Lodge is good 

 enough to refer me to some experiments on the anti- 

 septic action of sunlight which he carried out long 

 ago in association with the late Prof. Marshall Ward. 

 I have not yet been able to see the memoir to which 

 Sir Oliver Lodge refers, but I believe that I am 

 already well acquainted with it, and have been able 

 to quote its essential findings on many occasions in 

 connection with the demand for the abolition of the 

 coal-smoke curse— thanks to an admirable account of 

 Marshall Ward's methods and results, referred to the 

 year 1802, in Sir James Crichton-Browne's " Light 

 and Sanitation," an address delivered in Manchester 

 in iqo2 (Sherratt and Hughes, 27 St. Ann .Street, 

 Manchester). Particularly I value the last para- 

 graph, in which Sir Oliver Lodge praises the anti- 



