162 
common. Acetylene burnt with an equal volume 
of oxygen gives a temperature which is 1000° C. 
higher than the oxy-hydrogen flame. For suc- 
cessful welding minute attention to the details of 
construction of the blowpipes is necessary, and 
the author describes the forms of blowpipes used 
and the generators for producing acetylene 
economically. 
The enormous extent to which this form of 
welding is employed in the arts may be gathered 
from the descriptions of iron and mild steel welds 
that can be done in situ on large pieces of struc- 
tures and machinery. From repairing a large 
rudder of a steamer to the delicate junction of 
rose-petals in ornamental wrought iron work, the 
usefulness of the oxy-acetylene blowpipe extends, 
but perhaps the most important application of the 
blowpipe is in the cutting of metals and removing 
rivets. The weakest part of the work is in the 
translation, which in places leaves much to be 
desired. 
Ambidexterity and Mental Culture. By Dr. H. 
Macnaughton- Jones. Pp. , :02.. . (London: 
William Heinemann, 1914.) Price 2s. 6d. net. 
Tue author’s object in this little volume has been 
to state briefly the conclusions that may be drawn 
from the authoritative opinions of physiologists, 
psychologists, and teachers in different parts of 
the world as to the advantages of ambidexterity 
and the desirability of teaching it. Recent ex- 
perience is drawn upon, and accounts’ of 
“Eurythmics” and the Montessori system are 
included. 
LETTERS! OL GEE DEIPOR, 
[The Editor does not hold himself responsible for 
opinions expressed by his correspondents. Neither 
can he undertake to return, or to correspond with 
the writers of, rejected manuscripts intended for 
this or any other part of Nature. No notice is 
taken of anonymous communications. | 
Cellular Structure of Emulsions. 
WHILE preparing emulsions of radio-active minerals 
in alcohol for a ray examination, my assistant, Mr. 
E. K. Denton, directed my attention to the mottled 
appearance of the surface of the emulsion. Closer 
examination with a lens or low-power microscope 
shows that the surface is divided into numerous poly- 
gonal cells. At the centre of each cell the liquid is 
flowing vertically upwards, on the surface horizontally 
outwards, then downwards at the edges of the ceil 
and horizontally inwards along the bottom; such a 
circulation, in fact, as would be produced by a ver- 
tical doublet at the centre of the cell. The hydro- 
dynamical action of these doublets is no doubt respon- 
sible for the cellular structure, and the flow is main- 
tained by the evaporation of the alcohol at these 
centres. 
The effect may be obtained with an emulsion of an 
insoluble powder in any volatile liquid. I have found 
it, e.g. with carborundum, graphite, and lycopodium 
in ether, alcohol, or molten paraffin. (Certain pow- 
ders, such as rouge, fail to show it.) The accompany- 
ing photograph (graphite in methylated spirits) shows 
the general appearance of the surface, but does not 
give an adequate idea of the sharplv rectilinear char- 
acter of the boundaries of the cells. 
It seems possible that this effect is related to the 
NO; (2320, ViOL2 63 | 
NATURE 
[APRIL 16, 1914 
formation of flocculi in the solar photosphere, and 
even to terrestrial cloud formations of flocculent type. 
I have not been able to find previous reference to it, 
and should be obliged to any of your readers who 
can supply me with such or otherwise comment upon 
it KERR GRANT. 
The University of Adelaide, March 1. 
A Simple Method of Aerating Marine and other Aquaria. 
Tue following method is adapted for aerating 
aquaria, especially those which contain microscopic 
organisms, such as Ameeba, Vorticella, Hydra, 
Desmids, Diatoms, and delicate Algz. Further, the 
method is admirably suited for marine aquaria, and 
when once set up the sea-water does not require to 
be renewed but only maintained at its original level 
in the aquarium by the addition of distilled water. 
The apparatus required is readily obtained and 
fitted up; and as the cost is only a few shillings, it 
should appeal to all teachers of nature-study. Apart 
from the fascination of having several fresh-water and 
marine aquaria maintained in perfect condition, there 
is the educational value to be considered. 
All that is required is a water pump, a Woulff’s 
bottle, some glass tubing, a short length of rubber 
tubing, and one or two screw clips. 
The apparatus is fitted up as shown in the accom- 
panying sketch. 
SCREW CLIP FOR REGULATING AIR INLET AE bie 
AIR OUTEETS SSS A OUTLET 
C 2 ae a 
ert a Foals l| ume 
=] BS EE } 
=== = 
—= l 
WOULFFS. 
| BOTTLE 
i TW 
{i 
Water OUTFLOW 
The pump is connected with the water supply tap, 
and when the water is turned on it passes through 
the pump, dragging air with it into the Woulff’s 
bottle; here the air and water separate, and since 
the water outflow is checked, the air fills the upper 
part of the bottle, and becomes compressed. The air 
being under pressure may either blow the water out 
of the bottle or bubble through the aquaria; the latter 
being the path of least resistance, produces the desired 
result, namely, complete aeration of the aquaria. 
E.tis W. GILDERSLEEVES. 
Physiological Laboratory, Bedford College, 
Regent’s Park, N.W. 
