438 
the peculiar organs of these insects, by 
which they are at will enabled to evolve 
light; but the source of which light is yet 
but imperfectly understood. 
A transparent Variety of Quartz which re- 
flects no Light, but appears perfectly black on 
its newly-fractured surface, has been dis- 
covered by Dr. Brewster; who after im- 
mersing it in oil, of similar refractive power 
with the quartz, found this blackness to 
disappear, after it had resisted the action of 
various strong acids applied hot; but on 
taking it out and clearing it from the -oil, 
its former properties perfectly returned. 
At length the doctor was led to conclude, 
that the blackness of the surface arose from 
the fractured surface being composed of 
short slendet filaments of quartz, so exceed- 
ingly small in diameter, as probably not to 
exceed one-fourth of the thickness of the 
thinnest soap bubble, or *000,000,3 of an 
inch! and, from its minuteness, unable to 
reflect a single ray of the strongest light. 
. Castorina, or the peculiar Principle of Cas- 
tor, has, by the analysis of M. Bizio, been 
obtained, in the form of small prismatic 
acicular chrystals, some lines in length, 
diaphronous and white. In ether these 
chrystals dissolve very readily ; when heated, 
they appear to boil and emit vapours, which 
burn brilliantly in the open air; distilled in 
close vessels, the usual products of vegetable 
substances are obtained from these chrys- 
tals, without any trace of their animal’origin. 
A Native Oil of Laurel, possessing very 
nearly similar properties to distilled spirits 
of turpentine, is said to issue copiously on 
incision, from the stem of a species of laurel 
tree, which grows wild in South America, 
between the rivers Oronooko and Parime : 
if this be the case, which is said hardly to 
exceed alcohol in specific gravity, to be 
colourless, and of an aromatic odour, might 
become a profitable object of commerce. 
The pretended New Metal Tychiwm.—The 
president of the Royal Society has ascer- 
tained iron to be the cause of the equivocal 
appearances exhibited by the argentiferous 
specimens transmitted to him under this 
new name. 
_ Colouring Trinkets of Jeweller’s Gold, so as 
to give them the appearance of pure gold, is 
effected by boiling the articles for a proper 
length of time in a dilute acid; by which, 
on the surface, and for a small depth be- 
neath it, the alloy of copper is dissolved, 
leaving a thin spongy casing of pure gold 
on the surface, which occasions while 
new the rich frosted appearance such 
trinkets exhibit ; but owing to the softness 
and porosity of the surface so obtained, un- 
less afterwards burnished, articles so co- 
loured ‘scratch and wear dull very rapidly. 
Dr. Macculloch, in Dr. Brewster’s new 
journal, No. 1, recommends a boiling so- 
lution of ammonia in water for such ‘co- 
louring. oHy 1 
Spirit of Philosophical Discovery. 
[Dec. 1, 
A Remedy for the Barrenness of Pear- Trees 
has been discovered by the Rev. G. Swaine : 
as has long been known with early beans, 
hautbois, strawberries, cucumbers, and 
melons, the bunches of flowers, or corym- 
bus of the pear, usually contains a greater 
number of florets than {the plant has 
strength properly to mature; and the re- 
medy in each case is to extirpate several of 
the uppermost florets as soon as they ap- 
pear. A beurre pear-tree, which previously 
had been barren, upon which Mr. S., who 
left only the three lower florets of each 
bunch, ripened fruit from almost every one 
of these reserved florets. The process failed, 
however, with a gansell’s bergamot, whose 
barrenness appeared, on investigation, to’ 
arise from the polar being shed before the 
anthers were ready for impregnation. The 
patronage of our Horticultural Societies,’ 
has already done wonders towards improy- 
ing useful vegetables and fruits, and more; 
may be expected from their laudable en- 
deavours. 
A very destructive Wood-boring small con- 
staceous Insect (the limnoria terebrans of Dr. 
Leach), has been detailed by Mr. Robert 
Stevenson, as quickly destroying oak, black 
birch, Memel and Norway fir piles, driven 
in the sea, on the skirts of the Bell Rock, 
in Scotland; but, fortunately, it appeared 
that teak-wood piles, driven by the side of 
the above, were left untouched. Hence 
Mr. S. advises, that sea-lock gates, and 
pile-work in the sea, should be constructed of 
teak-wood, in order to avoid the fate of the 
lock-gates, but a few years ago erected, on 
the Crinan Canal, and of the piers of the 
timber bridge at Montrose harbour. 
A Substitute for Oak Bark in Tanning has 
been found in New South Wales, in the 
bark of two species of Mimora trees, which 
is much used at Sidney, and some other 
places in that colony. In England, the 
supply of oak bark is so inadequate to the 
demand, that the tanneries, in the vicinity of 
London alone, use, annually, from 7 to 
8,000 tons of foreign bark from France and 
the Netherlands, at the expense of about 
£14 per ton; attempts are therefore mak- 
ing by Mr. T. Kent, under the patronage of 
the Society of Arts, to condense, in New 
South Wales, the active principles of the 
mimosa bark, into a soft or solid extract. 
Two tons of such extract have been im- 
ported, and it has been found, by Mr. 
Brewin, and other Bermondsey tanners, 
that a given weight of mimora extract, will 
tan as much leather as four to five times 
the same weight of oak bark of average 
quality. 
Red Snow. — Professor Hgardh, in a letter 
to Dr. Hooper (Journ. Scien.), ‘seems to 
have ascertained that the Red Snow ‘Observed 
by Captain Parry is an Alga, which he calls 
Rotococcus nivalis ; and that it may be found 
not only on all the Alps, or high mountains, 
in the spring, but~also on limestone, during 
the 
