is essential in order to solve such problems as long-range sound trans- 
mission of powerful sonars (SQS—26), occupation at the bottom in 
permanent or semipermanent structures and search for objects at or 
near the bottom. The study of the benthic boundary is now possible 
because of the development of recording devices and probes which 
measure temperature, velocity, and pressure fluctuations at great 
depths. 
The benthic boundary is a base for studying the earth below. 
Beneath the oceans the earth’s crust is thin, and environmental condi- 
tions for measurement are quiet. A recent surprising discovery is 
that standard geophysical methods of exploration (seismic, gravi- 
metric, magnetic, and geothermal) yield better results than on land. 
The greater technical difficulties of working on the sea bottom are 
more than compensated by advantages of a uniform environment. 
There remains, of course, great ambiguity about the deeper material. 
This can only be resolved by coring the sediments (JOIDES) and 
the layer beneath (MOHOLE). 
An opportunity exists for adapting other geophysical techniques 
developed on land for marine use. For example, measurements on the 
sea bottom of the fluctuating electric and magnetic fields at various 
frequencies could provide information about the variation of con- 
ductivity with depth; from this, one can, in principle infer internal 
temperature and ultimately horizontal stresses between oceans and 
continents. Our understanding of mountain making and of the very 
existence of oceans and continents depends on assessment of stresses 
at the margin of basins. 
It is now possible to make deep-ocean tide measurements from in- 
struments lowered to the seabed. Theories of the origin of the moon 
depend critically on the efficacy of tides in disposing of the mechanical 
energy of the earth-moon system. Do tides in the solid earth slow 
down the earth’s rotation and move the moon outward or are the ocean 
tides responsible? Additional tidal measurements on a global scale 
are required in order to settle the problem. 
Further understanding of the benthic boundary depends on con- 
tinued development of instruments operable at great depths. Many 
observational programs require data-collection over long periods of 
time, and substantial technological problems exist in collecting these 
data. Furthermore, the ocean bottom is not uniform, and isolated 
observations are unlikely to yield a proper view. We can thus expect 
continuing expansion of measurements on a global scale. The oppor- 
tunity exists for perhaps solving an important cosmological problem, 
and we recommend that tidal measurements be made for many parts 
of the oceans to determine once and for all the nature and magnitude 
of oceanic tidal friction. 
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