412 Intelligence and Miscellaneous Articles. 



III. For an amateur the following experiment will appear rather 

 strange, in which the quality of a strange voice will seem changed 

 by the resonance of the cavity of the mouth. One end of the 

 india-rubber tube is again placed in the ear and the other in the 

 mouth; the mouth is put in the various positions for a, o, a, 

 while another person sings or draws out a definite sound such as a. 

 With a suitable height of the voice speaking, according to the 

 position of the mouth, the vowels a, o, a are successively heard. — 

 Wiedemann's Annalen, No. 3, 1884. 



PSYCHROMETRICAL INVESTIGATIONS. BY J. M. PERNTER. 



Pernter has made psychrometrical observations on the Obir 

 (6722 feet above the sea-level) with Wild's ventilation-hygrometer, 

 Eegnault's dew-point hygrometer, and Schwackhofer's volumetric 

 hygrometer. These observations and the theoretical considerations 

 connected therewith lead to the following results : — 



1. The development of the psychrometer formula under the 

 assumption of convection does not lead to the goal, for the assump- 

 tion that the inflowing air is cooled by the wet-thermometer bulb 

 from t to t' does not hold. 



2. The investigation of the psychrometer formula by Maxwell 

 and Stefan for perfectly still air is quite correct for this condition. 

 It loses in exactitude if modified for air in motion ; but it gives 

 the following very close approximation, if we represent by the ex- 

 pression v/(t — t' + l) the " inertia" of the psychrometer when near 

 saturation (that is, the fact that with moist air the evaporation is 

 not rapid enough in comparison with the inflowing air) : — 



»-^ p ClT3r + ^l \ ( ^ + (^0+i} ; 



or making i> = o, 5 C. and inserting the numerical values, 

 A . A -P.WK»«{l+l}{(*-0 +j -5«-}. 



3. The member which depends on the radiation does not disap- 

 pear, therefore, even with air in violent motion ; with still air it is 

 as great as that depending on conduction. 



4. The constant a does not change for equal velocity of the air 

 and for equal pressure. With lower pressure it is smaller, and 

 probably in the ratio P/760. For 760 millim. we get for a the 

 value ^=3-0, and therefore for any given pressure P : a =3 P/760. 



5. The general result is that an exact formula for the psychro- 

 meter can scarcely be obtained, and that therefore we cannot expect 

 by means of the psychrometer to determine the pressure of vapour 

 to within 0*1 millim. — Beiblatter der Physik, vol. viii. p. 31. 



