(551) 
What part of this energy is converted into sound is unknown. 
Wesster *) values the “efficiency” at 0,0013 to 0,0038 ; Rarrrian *) 
on the other hand supposed in 1877 as a preliminary estimate, that 
all was converted into sound (“supposing the whole energy of the 
escaping air converted into sound and no dissipation on the way”). 
The truth will probably lie between these two, since we have always 
paid attention to clear and easy sounding. For such a case Max 
Wien remarked in 1888: A loss of energy certainly takes place, 
first on account of the fact that part of the air-current is not 
converted into sound-waves at all, but is lost by the formation 
of vortices, partly inside, partly outside the pipe. We shall see 
later that this part is small only for a definite position of the 
lip of the pipe and for a definite pressure. A second loss of 
energy takes place by friction on the walls of the pipe and by 
tremors imparted to them; a third on the way between source and 
observer by friction on the floor, motion of the air (wind) and 
viscosity of the air. This latter part especially is relatively large 
with RayLxiGH, since by viscosity a loss of energy of + 22°/, took 
place *). 
If 22°/; is considered relatively much, we may assume that Max 
Wien at that time supposed for the losses by other causes a similar 
or smaller amount. But whatever the “efficiency” of the supplied 
energy may have been, there is no reason for assuming that it has 
been appreciably different for the different pipes. The wooden pipes 
at any rate belonged to the same set of uniform pattern. So the 
method suffices for comparative measurements. 
While one observer read the scales of spirometer and manometer, 
the other moved to the greatest distance at which the tone was just 
heard and recognised (“Erkennungsschwelle”). This distance was 
then later taken as the radius of a hemisphere through which the 
energy of the sound spread. 
A. Experiments on the heath at Milligen. 
Perfectly level ground, trees only at 600 metres. Quiet, fine evening, 
October 19, 1904. Acoustical observer F. H. Quix, optical observer 
H. F. Minkema (See Table I). 
B. Experiments in the gallery of the university library. 
Afternoon of January 3, 1905. Acoustical observer H. Zwaarpr- 
MAKER, optical observer H. F. Minkema. (See Table II). 
1) A. G. Wesster Boltzmann’s Festschrift 1904 p. 870 
2) RAYLEIGH Proc. Roy. Soc. vol 26 p. 248 1877. 
3) M. Wies, Die Messung der Tonstärke, Inauguraldissertation. Berlin 1888 p. 45, 
