Evening star., 1942-04-14
Of Stors. Men
And Atoms
Notebook Of Science Progress
In Laboratory. Field
And Study

u" eoUVsotVsys SsSso
And Study
BY Thomas r. Henry.
One Of the most delicate recording In
struments ever devised has been per-
fected by United States Bureau of Mines
engineers to determine how walls are
knocked down and men killed by the in
visible and deadly shock waves from ex-
plosions.
This has become . vital problem In
modern war. Apparently nothing ma
terial hits the wall or the man, for the
blast may have occurred ysrds away.
The new instrument is the result Of
seven years Of research by engineers in
terested In measuring the destructive
force Of air blasts set up by explosions in
mines and quarries. 1t Is described a. .
"high-speed cathode ray recording sys-
tenn" which can measure time increments
as low as 70-millionths of q second and
can obtain written records OF . blasts
advance at $4,000 inches . second.
This super-sensitive recording system
measures the pressure Tin pounds per
square inch) that il thrown against .
building or other object by high ex-
plosives at varying distances. It indi-
Gates exactly the degree Of force neces-
sary to destroy windows and buildings
within range. 1t also records the
amount Of air blast that is reflected, or
bounced" from one building to another
following an explosion.
Experiments with the new instrument
reveal that the main air blast disturb
ance is caused by q positive pulse, or
outward pressure. lasting a few thou
sandths Of = second. This rises quickly
to maximum and drops OF slowly. The
outward pressure then is followed by
negative pulse, or vacuum, of longer
duration which also exerts q force on
any object within ita range. These facts.
says the Bureau Of Mines report, coincide
with descriptions Of the behavior of
demolition bombs given by experts from
observations in Madrid, Rotterdam and
London.
The investigations were not undertaken
rs military measure. A large number
Of civilian blasting operations are 10
Gated near residential districts. The pos
sible damage is Of exceptional interest
to mining engineers who must take re-
sponsibility for lives and property.
Earlier investigations used microphones
placed near arranged shots of explosives
Window glass smashing was tested with
varying charges Of explosives and pres
sure measurements were taken up to
distances of 1900 feet--over miles.
By means Of tables and charts COM
piled in the past two years, the Bureau
Of Mines announces. users Of industrial
explosives may limit and control the
extent Of air blast damage from detona-
tons in mines and quarries.
The experiments are expected to be
utilized to . considerable extent by mill
tary explosives experts. both in the
manufacture of bombs and In planning
defensive devices for civilian popula-
tions. This has lately become q major
problem Of civilian defense.
Up to the present there has been some
disagreement a to whether the destruc-
tive effects of blast waves were due to
the pressure Of the waves themselves or
to the vacuum which followed them Gre
ating . small cyclone. From the Bureau
Of Mines tests 1t appears that both must
be guarded against and that what ac-
tually does the damage depends on the
distance of the object.
The Bureau of Mines instrument even
measures the shock waves set up by
ordinary conversation in q closed room
at distances of . few feet The voice Of
. public speaker, 1t was found, created
waves about 100 times more intense.
Russia will be aided in its postwar
recovery from the "scorched earth" pol
icy by Sir John Russell, England's fore
most agricultural expert.
Armed with information gathered on
two trips through Russia, he will assist
Soviet officials in restoring the rich
grain producing provinces Of the south
to full fertility.
The inevitable result OF the policy, he
had pointed out. Is famine and pesti-
lence, necessitating large-scale relief and
widespread agricultural rehabilitation.
Fortunately, conditions in the Ukraine
have not favored soil erosion like that
in the dust bowl sections OF the United
States. Russian plant breeders have
produced varieties Of crops suitable to
different regions with special regard to
drought-resistant types Of grain.
1t would greatly facilitate reconstruc-
tion, Sir John says, If selected varieties
of grain could be sent to Western Cam
ada and the United States to multiply
in readiness for the time of need. Once
the seed was lost, he explains. 1t would
require many years to reproduce grain
suitably bred to meet soil and climatic
requirements.
Where Russian fruits are concerned,
Russell already has arranged for nu-
merous buds to be sent TO- England,