ae Oe 
Oct. 7, 1886] 
NATURE 
547 
mical to keep the prepared fibrin by drying it in a current of 
air than to preserve it under ether, as usually recommended, 
September 27 ARTHUR DOWNES 
Note on Actinometry by Oxalic Acid 
OXALIC acid is entirely oxidised by light (Proc. Ray. Soc. No. 
191, and Chemical News, October 8, 1880), and affords, by reason 
of its own physical properties and those of the products of the 
reaction, an excellent medium for actinometry. A preliminary 
series of experiments on the physical conditions which modify 
this oxidation show that, ¢.f., the effect is greater in direct pro- 
portion to the extent of exposed surface of the solution but in- 
versely as its depth. It is greater also in proportion to the 
strength of the solution ; and it would appear—I speak for the 
present quite provisionally—that in this relation the reaction 
follows a definite law, being as the square root of the mass. 
September 27 ARTHUR DOWNES 
Humming in the Air caused by Insects 
In a letter to the Hon. Daines Barrington (letter Ixxx.) the 
Rey. Gilbert White, the well-known author of the ‘‘ Natural 
History of Selborne,” mentions a strange humming sound in 
the air. He writes :—‘‘ There is a natural occurrence to be met 
with upon the highest parts of our downs in hot summer days 
which always amuses me much without giving me any satisfaction 
with respect to the cause of it : and that is a loud audible humming 
as of bees in the air, though not one insect is to beseen. This sound 
is to be heard distinctly the whole common through from the 
Money Dells to my avenue gate. Any person would suppose 
that a large swarm of bees was in motion, and playing about 
over his head. This noise was heard last week on June 28.” 
It is singular that no explanation has been offered by any one 
for such a common phenomenon. I am convinced that the 
humming sound mentioned by Gilbert White was nothing more 
than the noise occasioned by the vibrations of millions of insects’ 
wings in the air. In hot summer evenings in particular I have 
heard these peculiar humming sounds, and know them to be 
caused by immense hordes of gnats and midges which fill the air 
with their numbers. W. Harcourt BATH 
The Limes, Sutton Coldfield, near Birmingham, October 
Mimicry in Snakes 
A curious fact has been lately brought to my notice by a 
friend of mine, Mr. H. M. Oakley, in connection with the 
Dasypeltis scaber, Linn., or egg-eating snake—the ‘‘ Eijer eter” of 
the Dutch colonists—which, if not already well known, may 
prove of interest to some of your readers. The specimen ab- 
tained by Mr. Oakley was caught at Hout Bay some twenty 
miles from Cape Town, and is about 3 feet in length, and its 
size, markings, and colour bear sufficient resemblance to those 
of the Berg Adder (Clothes atropos, Linn.) to be easily mis- 
taken for that snake. It also has keeled scales, generally 
characteristic, at the Cape, of venomous species. Its head has, 
snakes, but, when aroused and alarmed or irritated, it flattens it 
out until it assumes the usual viperine shape of the ‘‘ club” ina 
playing card. It then coils as for a spring, erects its head 
with every appearance of anger, produces a hissing noise with 
its scales, not unlike the hiss of a puff adder or cobra, and darts 
forward as if to strike its fangs into its foe, and in every way 
exactly simulates the motions of an irritated berg adder. This 
snake has, however, neither fangs nor teeth (which, indeed, 
would not be required for egg-swallowing), and is not poisonous, 
a fact which was placed beyond doubt by Mr. Oakley repeatedly 
placing his finger in the reptile’s mouth. This seems a clear 
instance of mimicry of another species for defensive purposes, 
but I am not aware of another instance among ophidians. 
W. HAMMOND TOOKE 
Cape Town, Cape of Good Hope, September 8 
THE COLONIAL AND INDIAN EXHIBITION 
ONTINUING our review of the most noteworthy or 
_ interesting vegetable products now being exhibited 
at South Kensington, we find in close contiguity to those 
_ from British Guiana, described in NATURE, July T5, p. 242, 
_ the exhibits from 
however, the long lacertine shape distinctive, here, of harmless” 
Mauritius.—The entire collection, though not large, is 
one of some interest, and the vegetable kingdom plays by 
far the most important part in the exhibits. The collec- 
tion of fibres will attract attention as much for its com- 
pleteness as for the care with which they have been 
prepared. Many are of scientific interest only, being 
obtained from plants that could never be turned to com- 
mercial account, such, for instance, as Hyophorbe Ver- 
schafeltiz, Latania commersonit, Lodoicea sechellarum, 
Macrozamia spiralis, &c. This collection is exhibited 
by the Botanical Gardens, as is also a collection of 
woods of similar interest. Some notes on these 
woods are useful. Thus, we are told that Zecoma 
pentaphylla has a soft white wood, not much used, 
and that it is a moderate-sized shade-tree of rapid 
growth. Samples of the wood, however, grown in the 
West Indies, show a close and even grain, and are fairly 
hard—so hard, indeed, as to suggest its suitability for 
wood-engraving, for which purpose it has been tried in 
this country, and though not by any means equal to box- 
wood, was reported upon as likely to be found useful for 
some kinds of work. The soft wood of Ficus mauritiana 
is used in the colony both for firewood and for hollowing 
out for canoes, while the hard wood of the Ebony (Déos- 
pyros Ebenum), which is described as being either black 
or sometimes streaked with yellow and brown, is used for 
inlaying, furniture, and ornamental turnery. The Bois 
Maigre (waza verticillata) is said to produce a short- 
grained timber which decomposes rapidly, but when 
young it makes excellent walking-sticks, which are much 
sought for. TZerminalia Benzoin,a large tree, which has 
become scarce in Mauritius, produces a wood valued for 
many purposes. It would seem that the wood is some- 
times fragrant, for it is said that “some parts of the tree 
were once muchburntin Mauritius as an incense.” Another 
odoriferous wood is Noronhia Broomieana, called here 
Bois Sandal. The Carambole (Averrhoa Carambola), 
valued in India for the sake of its acid fruits, is planted 
in Mauritius for the same purpose, the fruits being eaten 
either raw or made into tarts. 
Probably the exhibits that attract most attention in the 
Mauritius Court are the fine samples of vanilla pods, 
covered as they are with an abundant coating of crystals, 
and shedding forth, even through the glass cases which 
cover them, the delicate fragrance for which vanilla is 
celebrated. 
Seychelles—Amongst these exhibits the Double Cocoa- 
Nut, or Cocoa de Mer (Lodozcea sechellarum) is the most 
prominent. The double form of the fruit, which is its 
normal condition, is well shown, as well as a triple-lobed 
nut, which is not very uncommon. Here also are fine 
samples of vanilla, nearly, if not quite, equal to those from 
Mauritius. Dried papaw juice and some remarkably 
good specimens of essential oils are shown, all of which 
are extremely creditable to the colony. 
Cyprus.—The vegetable products shown in this Court 
are not numerous, nor is there anything of novelty ex- 
cepting perhaps a peculiar black substance described as 
honey, from the Carob or Locust Bean (Cervatonia Siligua). 
The pods themselves are also exhibited, and their pro- 
duction, it. seems, has greatly increased in recent years, 
stimulated by an increasing demand, especially in this 
country, where they are used very largely in making the 
patent compound cattle-foods, in consequence of their 
saccharine and nutritious character. Low freights have 
much encouraged the trade in carobs, enabling shippers 
to sell them at moderate prices. The quantity of carobs 
exported from Cyprus in 1884 amounted to 30,000 
tons, about one-half of which came to England. The 
finest quality is produced in Limassol and Lefcara, and 
obtain relatively higher prices than those of Kyrenia. 
The average price realised for these pods is about 3/. per 
ton. 
Another product of great importance to Cyprus up to 
