Avueust 2, 1918] 
though he may not now know the actual 
details of the construction of such a craft, 
he soon sees the general requirements to be 
satisfied. Archimedes’s principle acquires 
a new interest. The laws of fluid pressure 
become more than text-book formulations 
of rare phenomena. His knowledge of the 
fact that water is practically incompres- 
sible enables him to criticize constructively 
such a story as told by the preacher who 
pictured to his horrified audience the 
wrecked Lusitania coursing the ocean ways 
at some far-down level below which no ship 
can ever sink. He sees new light when it 
dawns on him that even ‘‘the whys and 
why-nots of deep sea diving’’* come well 
within the field of discussion of an ordinary 
course in physics. Then again, the nation- 
wide interest in the conservation of am- 
monia for the manufacture of explosives 
lends new color to the whole subjects of 
heat and of gas phenomena, from the sim- 
ple laws of Boyle, of thermal expansion, of 
heat exchanges, to the applied side of re- 
frigeration. Perhaps for the first time he 
sees the reason for having a kinetic theory 
of gases. 
Next, perhaps, may come the field of 
sound, commonly considered as one of the 
minor branches of physics, a judgment 
somewhat justified, for in the more elemen- 
tary texts such as used in the high schools, 
this subject is allowed only from six to nine 
per cent. of the space in the book. And 
why? Surely not because its phenomena 
are fewer than those of the other phases of 
our science, not because they are of less im- 
portance, but rather, let us say, because 
they are less understood. After the United 
States entered the war and a census of our 
scientific abilities was taken, American 
physicists had to admit that after all no 
one knew very much about sound. The 
great sources of information were the works 
3 Scientific American, January 12, 1918, p. 60. 
SCIENCE 
103 
of Helmholtz and Rayleigh, treasure stores, 
to be sure, but limited in their applicability 
to practical problems, and containing little 
that could be recast into any form digest- 
ible by either practical workers or students. 
And then came real problems, thick and 
fast. Methods were sorely needed for lo- 
eating the enemy in the sea and in the air. 
In all of these directions some success has 
been attained, but until details are made 
public the physics teacher will have to 
supply what he can by way of suggesting 
the probable solutions of the problems. He 
knows something of the possibilities, some- 
thing of the conditions that must be satis- 
fied, and he is, or at least should be, free 
from the danger of the illogical reasoning of 
which others may be guilty. For example, 
he can assist his pupils in understanding 
how it is that suecessful methods can be de- 
vised for insulating a whole region against 
air-sounds and earth-sounds.* Doppler’s 
principle finds a new illustration in the phe- 
nomena produced by a near-by projectile.® 
Then there are those other questions, not so 
easily explained, such as those about the 
causes of distinct sound areas separated by 
a zone of silence which may be several miles 
in width, although the disturbance has orig- 
inated at a single source, as in the case of 
some of the explosions in East London.*° 
Such questions surely make new demands 
on the investigator and teacher, but at the 
same time they afford unequalled oppor- 
tunities for enlisting the interests of many 
to whom the subject has been wholly for- 
eign. 
For the first time artificially produced 
sounds are observed to have traveled as 
4 Elekt. Zeits., 38, pp. 410-441. Also Science 
Abstracts, A, No. 180, February, 1918. 
5 Science Abstracts, A, No. 528, 1917. 
6 Science Abstracts A, No. 1295, 1917. Phys. 
Zeit., 18, pp. 501-504. Science Abstracts, A, No. 
183, February, 1918. 
