May 21, 1914| 
NATURE 30 
ietq| 
valve. The pressure tending to reseat the valve is so 
arranged that it diminishes very rapidly as the valve 
lifts. In this way, when the flow of water 1s in- 
creased through the valve, the difference of pressure 
between its two sides decreases and thus represents 
one of the properties of the electric arc. When a 
steady flow is established and a column of water 
having a definite periodic time is connected to the 
valve oscillations can be set up similar to those 
obtained with an electric arc. Other properties of the 
arc discharge can also be demonstrated. 
The Cambridge Scientific Instrument Co.: An aero- 
dynamic balance. Designed for the experimental in- 
vestigation of the stability of aeroplanes. The main 
part of the balance consists of three arms mutually 
at right angles, each arm being counterbalanced. 
These arms meet in a point at which a steel centre is 
fixed, and the weight of the balance is taken on this 
point. The vertical arm passes through the under- 
side of a wind channel and supports the model under 
test. The horizontal arms are arranged respectively 
parallel and at right angles to the wind direction. 
The arrangements allow of the measurement of the 
forces on the model along three fixed rectangular 
axes, and also of the three moments about these axes 
for any angle of incidence of the wind on the model. 
Mr. F. W. Asten: A simple microbalance for the 
determination of the densities of small quantities of 
gases. The balance is made entirely of fused quartz, 
and consists of a beam of the simplest possible con- 
struction, bearing at one end a small closed bulb and 
at the other a solid counterpoise. The whole is sup. 
ported by a knife edge working on a polished quartz 
plate. The system is made to balance in air at some 
convenient pressure, and its sensitiveness made ex- 
tremely high, turning at about one-millionth of a milli- 
gram. The gas is admitted to the balance case and 
the pressure determined at which it causes the beam to 
balance in a given position. The corresponding pres- 
sure for a gas of known density (e.g. oxygen) is ¢hen 
measured, the ratio of the pressures giving the in- 
verse ratio of the densities. 
Mr: E. Leitz: A new binocular microscope. The 
body consists of a flat casing containing the system 
of prisms. At the upper end are situated two eye- 
pieces the distance apart of which can be regulated 
to suit the eyes of the observer by means of a milled 
head which actuates two levers inside the casing. 
The interpupillary distance can be varied between 54 
and 70 mm. The eyepiece tubes slide in guides so 
that dust cannot enter the prism casing. The left 
eyepiece tube is provided with an independent adjust- 
ment to accommodate eyes of unequal vision. All 
kinds of eyepieces and objectives may be used, and 
the instrument can be employed for the same purposes 
as the ordinary monocular microscope. An important 
feature in this microscope is the parallel eyepieces 
which obviate the actions of accommodation and ad- 
justment for convergence as is necessary in binocular 
microscopes constructed hitherto. Prof. A. W. Bicker- 
ton: The polyscope. A kaleidoscope rendered so 
optically perfect that a hundred reflections of a point 
or object may be seen. The angles of one are 30°. 
60°, and 90°; of the other, two angles 45° and one of 
go°. They produce two classes of patterns, one suit- 
able for textile fabrics, cretonnes, etc., the other suit- 
able for floor cloths, tiles, ete. The Polychromide 
Company (The Dover Sreet Studios, Ltd.): Instan- 
taneous photographs on paper taken in natural colour 
by the polychromide system. The optical separation 
of the natural colour of the object photographed is 
accomplished by means of the Hamburger-Conrady 
colour separation camera, which exposes three plates 
NO. 2325, VOL. 93| 
simultaneously—representing the red, yellow, and blue 
sensations in the superposed positives on gelatino- 
silver emulsions, which constitute the complete colour 
records exhibited. 
The National Physical Laboratory (Dr. W. Rosen- 
hain and Mr. J. L. Haughton): A new reagent for 
etching mild steel for microscopic examination. The 
reagent consists of an acid solution of ferric chloride 
containing small proportions of chlorides of copper and 
tin. Iron or steel sections exposed to this solution 
become covered with a very thin adherent layer of 
copper by a process of electrochemical substitution. 
This film of copper is deposited upon and thus darkens 
the ferrite areas, leaving the pearlite areas white, this 
effect being the reverse of that obtained with other 
reagents, such as picric acid. 
Prof. E. W. MacBride and Mr.°H. G. Newth: 
Double tadpoles of the frog, and double sea-urchins. 
The duplicity in the frog larve is of varying degree, 
and was produced experimentally. _Fertilised eggs 
were inverted immediately upon the completion of the 
first cleavage-furrow, and were kept inverted until 
gastrulation was complete. The duplicity in the sea- 
urchin larvz consists in the development of an urchin- 
rudiment on both sides, or of pedicellariz on both 
sides, whereas the normal larva has its rudiment on 
the left, its pedicellariz on the right. Dr. W. T. 
Calman: Bathynella natans, a Crustacean of the order 
Anaspidacea. This minute Crustacean has hitherto 
been known only from a solitary specimen obtained 
in 1882, by Prof. Vejdovsky from a well in Prague. 
It has recently been re-discovered in a well near Basle 
by M. Chappuis, by whom specimens have been sent 
to the British Museum (Natural History). It is a 
blind and otherwise degenerate member of. the 
Anaspidacea, an ancient and primitive order of Crus- 
tacea represented by fossils in carboniferous rocks of 
Europe and America, and by three other recent species 
in Australia and Tasmania. The Zoological Depart- 
ment of the British Museum (Nat. Hist.): Cast of the 
‘‘paddle”’ or fore limb of a humpback whale. The 
humpback is the species of whale which has been 
' most hunted during the last few years in Subantarctic 
waters. Immense numbers of these animals have 
been killed annually, and it can scarcely be doubted 
that the number will be enormously reduced unless 
steps are taken to control the rate of destruction. 
The late Major G. E. H. Barrett-Hamilton was sent 
to South Georgia by the Colonial Office, at the end of 
1913, in order to obtain information with regard to 
whales and whaling in the far south. He died during 
the progress of his investigations. The cast shown 
measures 14 ft. 6 in. in length, and illustrates one of 
the most striking peculiarities of the humpback, the 
paddles of which are exceptionally long. 
Dr. H, Eltringham: Preparations showing the 
urticating apparatus in Porthesia similis (gold tail 
moth). The female insect has long been known to 
| possess urticating properties similar to those of the 
larva. It has lately been proved that the moth 
deliberately collects the spicules shed by its larva, and 
by means of a special apparatus stores them in the 
anal tuft. Thev subsequently serve as a protection 
for the eggs. Prof E. B. Poulton: A family of 
Papilio dardanus, bred by Mr. W. A. Lamborn, near 
Lagos, S. Nigeria. The family was bred from a cap- 
tured female of the hippocoon form—the black and 
white butterfly, which is by far the commonest female 
form of this species in the locality. Six previous 
| families, bred by W. A. Lamborn from the same 
female form, contained hippocoon females and no 
others. This, the seventh, contains approximately 
equal numbers of hippocoon and dionysus, a non- 
