1254 
tion sketch of Fig. 2 for the point source, measurements 
of temperature and velocity made by Yih at the lowa 
Institute over a considerable range of distance and 
heat output could thus be generalized in the composite 
dimensionless plots shown in Fig. 3. Noteworthy is the 
(et) 
Vv 
(G/px)!73 
fo) fe) 
0.20 O16 O12 0.08 0.04 O 0.04 0.08 O12 O16 0.20 
r/x 
Fic. 3.—Dimensionless representation of experimental results 
for the conditions of Fig. 2. 
fact that for any particular value of r/x a number of the 
Froude type—F = 0/V/ zAy/p—is constant, indicat- 
ing that the phenomenon is truly gravitational in its 
fundamental aspects. 
Summary and Conclusions 
Through the many professions dealing with fluid 
motion, there has been obtained a considerable amount 
of experience with scale-model investigations, which 
should be of use in developing comparable procedures 
for research in the field of meteorology. The general 
principles of dimensional analysis at once indicate the 
criteria for similarity of the various pertinent flow 
phenomena, and at the same time serve as a guide for 
effective research. Likewise, the closely related aspects 
of many problems in fluid motion make various tech- 
niques developed in other fields directly applicable to 
that in question. In other words, the scale model is now 
an established rather than an untried scientific tool, and 
the problem is one of adaptation to somewhat new 
requirements rather than of complete origination. 
Nevertheless, too great emphasis cannot be given 
to the fact that each of the professions now utilizing 
model techniques has perfected them only through 
many years of painstaking labor. Dimensional analysis 
is an invaluable guide but in no sense an automatic 
control, and its proper use continues to depend upon 
sound experience both in selecting the essential vari- 
ables and in reducing to a practicable form the complex 
relationship which usually results. Moreover, the extent 
to which special requirements of each particular field 
govern the experimental techniques can be thoroughly 
understood only through actual laboratory contact. 
The fact therefore remains that the foregoing presenta- 
tion by one who is only imdirectly familiar with the 
problems of this specific field can be but a rough indica- 
tion of the situation which should exist after a number 
of years of direct accomplishment by future specialists. 
At present writing it appears that meteorologists could 
profitably expand, according to their own requirements, 
many aspects of model investigations already proven 
useful in related fields. These include studies of both the 
LABORATORY INVESTIGATIONS 
mean flow pattern and the eddy structure produced by 
irregular boundary configurations; research in the dif- 
fusion of heat and vapor by both forced and free con- 
vection; experiments on stratified flows; and—at least 
in an exploratory manner—the simulation of conditions 
which combine two or more such effects. To what 
extent attainment of the Reynolds criterion of viscous 
similitude may become possible for other boundary 
conditions, and whether or not thermodynamic similar- 
ity may also become practicable, must be decided in the 
future. In any event, the profession can rest assured 
that the perfection of meteorological model techniques 
will open many an avenue of fruitful study hardly con- 
ceivable in advance. 
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