116 

the Fraunhofer effect has now been established in the 
case of the spectrum of an organic compound of complex 
structure. 
A more detailed account of this work will be 
published almost immediately. We wish to reserve 
this particular group of spectra for our own investiga- 
tion, as we have already planned and in part carried 
out a connected series of investigations upon it, 
which we wish to complete before venturing upon 
the theory of the matter. We hope also to investigate 
the behaviour of solutions under the influence of the 
Tesla discharge. 
J. K. Marsu. 
A. W. STEWART. 
The Sir Donald Currie Laboratories, 
The Queen’s University of Belfast, 
January 8. 

Distribution of the Organ-Pipe Diatom 
(Bacillaria paradoxa). 
In connexion with the interesting question raised 
by Mr. F. Chapman in Nature of January 6, p. 15, 
as to the peculiar movements of Bacillavia paradoxa 
being due to osmotic pressure, I am writing to say 
that all the specimens observed by Mr. H. Weaver 
and myself that were gathered from the Staffordshire 
and Worcestershire Canal at Stourport and from 
ponds at Wilden and Hartlebury (see Nature, vol. 
108, p. 163) were very active and so continued during 
the period we kept them under observation (about 
a week in each case), The water in this canal and 
in these ponds is some eighty miles removed from the 
sea, It is quite fresh and not at all brackish. 
J. W. Wixtiams. 
67 Load Street, Bewdley, Worcs. 
Experiments on Hardness and Penetration. 
As a student of colloidal chemistry I was much 
interested in the results of the experiments on the 
clay-water systems by Mr. A. S. E. Ackermann 
(NATURE, January 6, p. 17), showing that there was a 
continuous penetration of the systems by a heavy 
object when its pressure exceeded a certain critical 
value referred to as the ‘‘ pressure of fluidity.”’ 
The phenomenon has been observed in many 
colloidal systems and also with the coarser systems 
such as paints, thick oils, etc. Bingham found zero 
fluidity or infinite viscosity with 4 per cent. china clay 
or 5°5 per cent. of graphite. E. Hatschek, investigat- 
ing aqueous solutions of gelatine, showed that the 
viscosity varied with the rate of shear, and a similar 
conclusion was reached by Hatschek and Humphrey, 
working with systems of sifted rice particles in toluene- 
carbon tetrachloride. In general, at the lower rates 
of shear the viscosity is abnormally high and even 
infinite if the system be coarse-textured. 
With the Stormer type of viscometer the curve 
relating the number of revolutions per minute of the 
cylinder rotating in a coarse system such as a paint 
or grease, with the load rotating it, is curvilinear and 
does not pass through the origin. 
The minimum load required to start rotation, apart 
from that to overcome the friction of the apparatus, 
would correspond to the “‘ yield point” obtained by 
the use of Bingham and Green’s plastometer, or the 
“ pressure of fluidity ’’ by Mr. Ackermann. 
It is evident that the viscosity of these systems has 
lost its usual significance since it is a variable function 
and any value obtained by any one method is empirical. 
This would apply to the value given by Mr. Ackermann 
for the viscosity of lead in the solid state. 
Another interesting phenomenon in this connexion 
NO. 2778, VOL. I11] 
NATURE 


[JANUARY 27, 1923, 
is that the rate of penetration by the object gradually 
decreases and eventually ceases; thus a steel ball 
remains suspended in a well-mixed paint after a fall 
of some distance. With some oils, a falling sphere 
cuts a path through the liquid, $0 that the apparent 
viscosity decreases with each determination by the 
falling sphere method. E, MARDLEs. 
2 Hillfield Villas, Union Street, 
Farnborough, January 9. 

Ir is with great interest that I read Mr. Ackermann’s 
letter in Nature of January 6, p. 17, with regard to 
the penetration of clay and lead by a loaded disc. 
The manuscript of a paper intended for the next 
meeting of the Iron and Steel Institute is now com- 
plete. The work deals with several of the deduc- 
tions to be made from my formula for Brinell hardness 
(NaturE, December 9, vol. 110, p. 773). 
While clay has not been examined, tests have been 
carried out on pitch and plasticine. Meyer’s formula 
appears to be true for these two materials. 
Hucu O'NEILL. 
The Victoria University of Manchester, 
January 9. 

A New Gregarine Parasite of Leptoplana. 
Mr. Sam SETNA, who is working under my super- 
vision on the Polycystid Gregarines, has just found 
specimens of a Cephaline Gregarine infesting a speci- 
men of Leptoplana sp. recently obtained from the 
Marine Biological Laboratory at Plymouth. This 
Gregarine seems to be rather a rare parasite of 
Leptoplana, as no Gregarine has been described before 
from Leptoplana, according to lists given by Minchin 
(1903) and Watson (1916), or in literature published 
since. Indeed, extraordinarily few Sporozoa have 
been found from the Platyhelminthes as a whole. 
The find is all the more remarkable as Leptoplana is 
so commonly used as a type animal. Only a single 
specimen was found to be infected, and other speci- 
mens in the same tube that have been examined do 
not show the infection. 
In the sections of the infected worm, a number of 
individuals of the Gregarine have been found in the 
parenchyma of its body. The trophozoite is solitary 
and quite large in size, measuring from 103 » to 168 u 
inlength. The protomerite is quite distinctly marked 
off from the deutomerite. Only one young individual 
has been found showing the epimerite. The latter is 
large, hemispherical, and simple. The nucleus is large 
and rounded and measures 19 » to 23 “in diameter, and 
exhibits the characteristic Gregarine structure, with a 
slightly eccentrically placed karyosome and a number 
of chromatin particles disposed round it. 
Unfortunately, no other stages of the life-history 
have been encountered, and it is consequently im- 
possible to refer the parasite to any particular genus. 
B. L. Buatta. 
Zoological Laboratory. 
Government College, Lahore, 
November 23. 

Discovery of the Use of Phosphates as Fertilisers. 
In view of the interest attaching to the so-called 
artificial fertilisers, it may be worth recording that 
the idea of the possibility of utilising raw mineral 
phosphates as phosphatic fertiliser is to be found in 
the current agricultural publications some years before 
1840, the date usually regarded as that of the first 
serious record. 
In 1842 Lawes took out his patent for the manu- 
facture of superphosphate. In a question of infringe- 

