because it is long enough to yield reliable results. Before so doing, 
however, interesting results can be deduced just on the basis of the 
fact that the record is Gaussian. 
The twenty-five minute record was recorded on ordinary chart 
paper (such as is shown in Figure 12) at a fairly rapid speed of 6 
inches equal to one minute. The range of the record covers from 
extreme to extreme about seven or eight of the small chart divisions. 
The standard deviation of the record was found from one hundred 
points picked at random. An arbitrary zero was chosen as a line 
well below the record and the square root of the second moment about 
the computed mean of the sample as measured from this arbitrary mean 
was found. By some strange accident, the mean of the sample fell 
right on one of the scale lines within a few thousandths of a unit, 
and thus the estimated mean of the record falls, within the accuracy 
of the measurements, on one of the chart lines. 
Now suppose that the mean and standard deviation of the sample 
which was taken are close to the true mean and standard deviation 
of the record. Then another sample of one hundred other points 
chosen at random would have nearly the same mean and standard de- 
viation. In fact, an infinite number of different samples of points 
could be taken from the record and if the points were far enough 
apart, each sample would have essentially the same mean and standard 
deviation. More technically the means should be normally distributed 
with a mean near the true mean, etc. The only thing that could not 
be done would be to take a sample of one hundred points from, say, 
a portion of the record one second long such that the points were 
only one one hundredth of a second apart. In this case, Since the 
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