196 
IOWA ACADEMY OP SCIENCE 
sure is greater for the higher pitches. For a pressure increase of from 
2 units to 3 units, the rise in pitch was as follows : 
Pitch 
Rise 
200 
250 
300. 
350. 
400. 
5.69 
5.79 
.6.37 
.7.79 
.9.08 
The variator is most reliable at the lowest pressure which will cause 
it to sound. The mean variation at 3 units pressure was 0.70, while at 
1.5 units pressure it was only 0.29. The low pressure gives a pure, 
steady tone, quite free from anj?- pinched or hissing quality. 
A similar study was made of the effect of changing the position of 
the mouth-piece. Raising the mouth-piece above the level of the top of 
the bottle lowers the pitch. This is greater when the mouth-piece is 
already in a high position than when it is low. Thus, a change in gap 
of 3 mm. to 4.3 mm. lowered the pitch as much as a change from 0 to 
3 mm. Again, a change in gap from 1.95 mm. to 3.90 mm. caused a rise 
of 4.80 vd., while a change from 0 to 1.95 mm. gave a rise of only 2.33 
vd. The greatest change in pitch that can be made by changing the 
position of the mouth-piece is about 10 vibrations. The best position 
for the mouth-piece is thi highest that will produce a tone. Set at 0, 
the results showed a mean variation of 0.6 ; at 3 mm. gap, a mean var- 
iation of 0.4; and at 4.3 mm. gap, a mean variation of but 0.1. There 
is a most favorable mouth-piece position for each pitch, the higher 
tones requiring a narrower gap. The wider gap requires a stronger 
pressure. It is also worthy of note that the 200 vd. to 400 vd. size of , 
variator is most reliable at between 250 vd. and 270 vd. 
The manner in which the instrument’s mouth-piece is attached is 
very unsatisfactory. It should be absolutely firm, accurately adjust- 
able, and provided with a. setting scale showing the Vvidth of the gap. 
The piston sometimes settles downward. It must be fitted with a 
clamping device. At the lowest pressures, some tones which give no 
audible sound, produce a clear reading in the tonoscope. Such tones 
must be started by the operator’s blowing into the variator and start- 
ing the general air movement required. The securing of a steady air 
stream is a serious problem. As noted earlier, the slightest pressure 
change causes a considerable change in pitch. The Whipple tanks are 
perhaps the best contrivance, but they demand very close care, and 
are at best a frequent source of error. 
