( 550 ) 
these parallel investigations were concordant in some respects, different 
in others. They agree in this that: 
1s*. there is only one maximum of sensitiveness ; 
2nd, that this maximum lies at g*; 
3rd, that the zone of fair sensitiveness extends from c’ to gq’. 
4th that outside this region toward the limits of the scale the 
‘sensitiveness diminishes very strongly. 
They differ in this that: 
1st. with Max Wier the sensitiveness still diverges very much 
within the zone of fair sensitiveness, whereas with us it is of the 
same order. 
2nd. that the perceptible minimum for the most sensitive point is 
with him 100.000.000 times smaller than with us. 
In this state of affairs it seemed desirable once more to determine 
the perceptible minima throughout the whole scale by an entirely 
different method. Telephone as well as tuning-forks ought thereby 
to be avoided. So we had recourse to wide roofed organ pipes of 
which a wooden set of uniform pattern, extending from C to g* 
was at our disposal which partly coincided with the well-known 
Epr~Mann whistles and could be continued by the Galton whistle. 
Some series of such experiments were made, partly on the heath 
at Milligen, partly in the gallery of the university library at Utrecht, 
partly in the sound-tight room of the physiological-laboratory. Since 
the results, generally speaking, agree fairly well and a full account 
of them will be published later, for the present only two series 
taken under the simplest conditions, will be dealt with. These are: 
a, the concluding series on the heath, 6, in the gallery. The arran- 
gement, which was the same for both, will first be deseribed. 
The organ pipe which serves as the source of sound, is mounted 
vertically on a stand, near the floor, with as little contact as possible. 
It is connected with a Hurcuinson spirometer. Close under the air- 
room of the organ pipe and connected with this latter by a wide 
opening, is a ligroine manometer. The manometer being bent 
into an obtuse angle as little as */, mm. of waterpressure can be 
read. The spirometer is now loaded with a little box containing 
sand, so that it forces out the air very regularly and causes the 
organ pipe to emit a soft sound without an audible frictional noise 
and without partial tones. The air used is read off on the scale of 
the spirometer and calculated per second by at the same time starting 
a timing watch. The product of the volume of air, pressure and 
acceleration of gravity (all in em.) then give the energy supplied 
per second in ergs. 
