calculated for a series of temperatai'es and compared with the values 

 found experimentally. They are collected in table VIII. 

 TABLE VIII. 



Considering the inaccuracy of the extrapolation of T\ over fully 

 200^ below the field of observation, the agreement may be called 

 a complete one. It furnishes a proof of the correctness of our mea- 

 surements as well as of those of WTihikk in connexion with the dis- 

 sociation of copper oxide. 



Delft, Inorg. and pliys. chem. Inhoratory 

 of tlie Technical University. 



Physiology. — ''On mea.snrewent 0/ soimd." By Prof. H. Z\v.\.\rde- 



MAKER. 



(Goramuiiicalecl in llie niueling of April 1015.) 



I have previously poinleil out the benetit to be derived from Lord 

 Ratleigh's arrangement, if we wish to perform a relative or even 

 an absolute measurement of sound. Originally ') it was applied to 

 the measurement of stationary sound-waves. W. König") extended 

 its use to the theory of progressive waves in detail. It also enabled 

 W. Zernov') to carry out experiments on the intensity of the 

 human voice. All earlier researchers and myself at first also, gave 

 to the mirror, which was placed obliquely to the sound-wave, a 

 peculiar position by attaching to it a small magnet. I now departed 

 from this principle, at first by biiilar suspension, aftei'wards by simply 

 hanging the mirror up by a long Wollaston fibre, flattened or not. ") 



1) Lord Rayleigh. Scienlific Pape'-s. Vol II, p. 132. 



2) W. KöNiG. Ann. d. Physik. Bd. 42 and 43, 1891. 



?) W. Zebnov. Ami. d. Physik. (4). Bd 24 p. 79, 1908. 



^) H. ZwAAüDEMAKER. "On hearing-appaiatus". Ned. Tijdschrift v Geneesk. 



1912, II. p. 1101. Proc. of the meeling of 27 Sept. 1913. Vol. 22. p. 273, 

 Congress at Delft, March 1913, Multiple resonantie. Ned. Tijdschr. v. Geneesk., 



1913. II. p. 640. 



12 

 ProceedJiugs Royal Acad. AuiSlerdaui. Vol. XVIll. 



