AUGUST 6, 1914] 
NATURE 
Sfeie, 
laboratory for the estimation of acidity in peats from 
different types of moors. The most satisfactory re- 
sults were obtained by treatment of the peat with 
calcium acetate and estimation of the free acid result- 
ing. 
Dr. Tacke (Bremen) supported the method adopted 
at Bremen, 1.e. neutralisation with CaCO,, on the 
ground that it involves the actual practical method of 
getting rid of acidity in moors. Moreover, whether 
the acid properties are due to the presence of actual 
acids or to colloids, CaCO, is the best and most 
commonly applied neutraliser. 
Tacke’s method found many supporters who fre- 
quently use it and have always found it efficient. 
Results obtained at Bremen with the two methods, 
CaCO, and calcium acetate, agreed very well. It 
became at once noticeable that the former diversity 
of opinions between the stations at Bremen and 
Munich, as to the nature of soil acidity, no longer 
exists to the same extent. It appears to be generally 
accepted that the acidity of sour soils may be due to 
the presence of both actual acids and colloids. Tacke 
still maintains that the fact that most colloids present 
in soils are acid is sufficient to account for the views 
previously put forward by Baumann and Gully. 
The discussion was chiefly remarkable for bringing 
out the large number of methods which have been 
employed by different workers. These included the 
direct method of obtaining an alkali extract, precipi- 
tating the brown colloidal matter 
with neutral calcium chloride, and 
titrating the clear solution. Another 
method was the estimation of the 
H ions in a water extract. It was 
considered that much more research 
is required before any particular 
method can be adopted officially. 
A committee, consisting of Prof. 
Albert, Prof. Rindell, Dr. Tacke, 
and Dr. Gully was appointed to 
test thoroughly the different 
methods. 0 
After the meeting the members of 
the commission were conducted by 
Prof. Kraus through an interesting 
collection of soils in his laboratory, including typical 
agricultural soils of Bavaria and other German States 
and also a large collection from the German colony 
of Togo; then by Prof. Henkel through the other 
laboratories of the agricultural section of the Munich 
Technical High School. ALA ET: 
Thee Shak S AROUND FHEINORTH POLE.! 
HIS is a mathematical problem which can be 
solved fairly easily, and the answer is that the stars 
must be distributed in distance according to a law 
shown graphically by the curve in Fig. IV. (The 
eee Hs hig 
distribution of velocities —j7-e~"*"*dyv combined with the 
Nr 
distribution of proper motions gee) “ leads to the 
a a 
patial distribution 2a*h?re~ lr? dp), 
In the diagram, distances are measured horizontally, 
the unit of distance being that at which a star’s 
parallax is equal to 1” (or 206,265 times the distance 
of the earth from the sun). It is convenient to have 
a name for this unit, and in what follows the word 
Parsec, suggested by Prof. Turner, will be adopted. 
With this unit a distance of 100 in the diagram 
denotes twenty million times the distance of the sun 
1 Diseeurse delivered at the Royal Institution on Friday, April 24, by 
Dr. F. W. Dyson, F.R.S. Continued from p. 576. 
NO.( 2336, VOL. 93| 
40 8100 200 300 400 5090 600 7090 800 $00 
Fic. 4.—Distribution in distance of the stars in Carrington’s Catalogue. 
from the earth. The following table gives the per- 
centage of stars between certain limits of distance :— 
TaBie IV. 
6 per cent. of the stars are between o and 100 parsecs 
5 » 9 % LOOs ,nt2 COME 
10 9 ” ” 200 ” 400 ” 
43 9 ” 39 400 ? 7090 ” 
36 ” 9 ” = 700 ” 
It follows that 88 per cent. of the stars in Carring- 
ton’s Catalogue—that is, 88 per cent. of all the stars 
brighter than about 10°5 magnitude—lie between 20 
and 150 million times the distance of the sun from 
the earth. This law of the distribution of the stars 
is at first sight rather surprising. It should be 
remembered that the only stars at a great distance 
which are included are those which are intrinsically 
very bright, and these form only a small proportion 
of all the stars. Prof. Eddington has found that a 
similar law holds for stars brighter than 6-0 magni- 
tude. 
Having found the law of distribution of the dis- 
tances of these stars, it is not difficult to determine 
something about their absolute luminosities, 1.e. how 
they would compare with the sun in brightness if 
placed at an equal distance from us. 
If the sun were at a distance of one parsec, it 
would appear as a bright star, brighter than the first 
1090 PARSECS 
magnitude—actually of magnitude 05; if at a dis- 
tance of 100 parsecs, its magnitude would be 10's. 
Now all the stars in Carrington’s Catalogue may be 
taken as brighter than 10°5 magnitude, thus at least 
gs per cent. of these stars are intrinsically brighter 
than the sun, and at least 80 per cent. are four 
times as bright, 40 per cent. are sixteen times as 
bright, and 8 per cent. are fifty times as bright. 
We may conclude that the great majority of the 
stars brighter than 10°5 magnitude are intrinsically 
brighter than the sun, and a considerable proportion 
very much brighter. ; Of 
The distribution of bright and faint stars in a given 
volume of space is quite different, and contains a 
much larger proportion of faint stars. If we make 
the assumptions that the density of the stars and the 
proportions of bright and faint ones is the same at 
the different distances from the sun within which 
| these Carrington stars are situated, it is possible to 
find the actual number of stars of different luminosi- 
| ties in a given volume of space. 
In a sphere with 
or twenty million times the 
radius 100 parsecs, 
| distance of the earth from the sun, there are, at least, 
24 which are 100 times as luminous as the sun 
340 ” 50 Ph] ” ” 
1,53 bh) 25 ” ” ” 
4,840 9 ite) ” ”? 3” 
23,200 ” I 9 ig ” 
93,300 39 jsth the luminosity of the sun. 
