Magnetic Spherules — Pettersson and Frederiksson 
79 
Spherules per kg salt-and carbonate -free sediment. 
0 200 400 600 
Fig. 8. Number of spherules per kg. of salt- and 
carbonate-free sediment from Core 187. 
different parts of the world (Bracewell, 1954) 
strong evidence has been produced for the 
influence of cosmic dust as condensation 
nuclei for raindrops. According to these finds 
there occur distinct maxima of precipitation 
on certain dates like January 12, 22, and 31 
to February 1. These peaks of rainfall occur 
29 to 30 days after the Earth has passed 
through meteor showers. According to Bowen 
the dust into which these meteors are dis- 
persed at great heights in the atmosphere 
takes about 30 days to descend to the upper 
troposphere, where a condensation of water- 
drops is produced which ultimately reach the 
Earth as rain. Through this condensation a 
depletion of water vapour in the upper atmos- 
phere is occasioned, decreasing the "green- 
house” effect on the radiation balance. 
It has even been surmised that an abnormal 
increase in the incidence of meteors may give 
rise, by a trigger action, to a deterioration 
of climate and possibly release a glacial epoch. 
No wonder that students of the atmos- 
phere and its radiation balance are taking a 
growing interest in meteoric dust. 
THE ANNUAL ACCRUEMENT OF COSMIC 
SPHERULES 
In trying to work out the total weight of 
the cosmic spherules settling on to the surface 
of our planet the numbers of spherules found 
in the cores investigated can be used, con- 
verting the numbers of spherules per kg. into 
weights. But already this conversion from 
numbers into weights implies an element of 
uncertainty. 
We have counted all spherules of a diam- 
eter exceeding 30 /x and then computed the 
total number accruing to the Earth for one 
year. These values are set out in column 7 of 
Table 3. In converting numbers into weights 
we have assumed a specific weight of 5.0 and 
a diameter of 40 n , assuming that all the 
spherules belong to the size-class 30-60 /x . 
When taking the total counted number in- 
stead of the number of the size-class 30-60 n, 
we add about 10 per cent as a correction for 
the weight of the spherules of a diameter less 
than 30 /x. In this way the values set out in 
column 8 have been obtained. Finally, column 
9 shows values of the total accruement of 
black spherules of all sizes, the value being 
three times higher than those in column 8. 
The factor 3 we obtain by considering that 
the number of spherules between 30 and 60 /x 
is 8 times higher than the number of spherules 
exceeding 60 /x in diameter. (See Table 2.) 
The weight of the spherules of 30-60 /jl is 
assumed to be equal to the weight of the 
fraction 60-125 /jl and 125-250 /x. 
TABLE 2 
CORE NO. 
TOTAL NUMBERS OF 
SPHERULES COUNTED 
NUMBERS 30-60 (X 
NUMBERS 60 n 
30-60 fi 
> 60 ii 
71 
349 
69 
5 
90 
2,634 
303 
9 
92 
115 
23 
5 
133 
326 
29 
11 
187 
507 
58 
9 
3,931 
482 
8 
