JUNE 3, 1915] 

NATURE 
375 

appliances are made to the best of specifications, 
but that they should be sold at these ridiculous 
prices when they are of the distinctly dangerous 
tin-can type, liable to burst easily, is very near 
fraud. 
It is to be hoped that the British Fire Preven- 
tion Committee will persevere in its propaganda 
and obtain legislation after the war is over, mak- 
ing it a penal offence to construct an extinguisher 
unless there are certain constructional safeguards 
to be settled from time to time by the Secretary 
of State as mechanical science advances. Good 
progress has already been made in this direction, 
and but for the war, the protection of the public 
against fraudulent fire appliances might have 
already been achieved. 
To our readers, however, this article should 
serve as one of warning to insist on a written 
warranty before payment for any extinguishers 
purchased, that it complies either with the British 
Fire Prevention Committee’s specification, or 
with those of the Board of Trade, H.M. Office of 
Works, or the Metropolitan Police. Further, for 
the best finished article they should not pay more 
than 25s. to 30s. when constructed to either of 
these specifications, but if in doubt as to the 
machine offered or the possibility of regularly 
testing and re-charging it, let them keep to the 
old bucket of water and hand-pump. They at 
least are trustworthy, and the most suitable for 
ordinary conditions. 

RESEARCH IN AERODYNAMICS.1 
qh work of the Aerodynamical Laboratory at 
Koutchino is less affected by the necessity 
for technical work than any other of the European 
laboratories. It is for this reason, in all prob- 
ability, that the latest bulletin makes a refreshing 
change from the publications of Eiffel and the 
Advisory Committee for Aeronautics. 
The production of miniature whirlwinds forms 
the subject of one series of experiments, and the 
results are illustrated by some very interesting 
photographs. Rotations, as apart from eddies, 
are of frequent occurrence in nature; they may 
be seen in the autumn by the movement of leaves, 
due to a wind over open ground. Similar move- 
ments of air are found on the floor of the room 
below the intake of a wind channel, and the 
phenomenon indicates how little we really know 
of the motion of real fluids. 
Perhaps the most interesting papers in the 
bulletin are two relating to the principle of 
dynamical similarity as applied to viscous fluids. 
Experiments with the same object were made by 
Osborne Reynolds, and recently Messrs. Stanton 
and Pannell have established the practical utility 
of the theory in the case of air, water, and oil 
flowing through pipes. 
One of the two papers above mentioned deals 
1 Bulletin de l'Institut Aérodynamique de Koutchino. Fasci- 
cule y. (Moscow: I. N. Kouchnéreff and Co., 1914.) 
NO. 2379, VOL. 95| 
Pp. 296. 
| with experiments on the surface friction of discs 
in air and water, the motion being one of rotation 
in their own plane. The agreement between 
theory and practice is complete. The second paper 
relates to the whole of the published information 
on the resistance of spheres in air and water, the 
results being very discordant amongst themselves. 
The conclusion is drawn that the conditions of 
the theory of dynamical similarity cannot in this 
case be satisfied experimentally with the necessary 
degree of exactitude. The results of the two 
papers are illustrated by Figs. 1 and 2. The first 
relates to the friction of discs, and in carrying 
out these experiments variations were made in 
three quantities of primary importance, the dia- 
meter and speed of rotation of the disc and the 

05 










es rT TT 
wre | 
aL Peat | 
mH a KH 
| HL 



005 t 























i 
000005 Nee 
Fic- 1. 
viscosity of the fluid. The ratio of the greatest 
diameter to the least was 10:1, the ratio of the 
extreme speeds 2:1, and the ratio of the kine- 
matic viscosities 13:1. The theory of dynamical 
similarity indicates that any one of these changes 
can be predicted from the effect of changes in 
either of the others, and the practical proof of 
this is the fact that the whole of the experimental 
results can be collected on a single curve as in 
Tig. 1. As the range of variation included a 
region of critical flow, as indicated by the dip in 
the curve, the practical agreement is a delicate 
test of the exactness with which the experimental 
conditions complied with the conditions of geo- 
metrical similarity. 

