244 
surface of heated glass, cleanly wiped, 
which is intended to be silvered; the me- 
tallic coat, thus formed, adheres very firmly 
and uniformly to the glass, provided that 
the amalgum is carefully skimmed, and the 
glass equally heated in every part, and 
allowed to cool in the same uniform 
manner. 
An Ear-trumpet, or hearing-tube, has 
lately been described and recommended by 
Dr. T. Morrison of Aberdeen, for the as- 
sistance of persons partially deaf,—which, 
instead of having its nearer end diminished, 
so as to enter the patient’s ear, and therein, 
not unfrequently, causing mischief, in case 
of the tube receiving any accidental thrust ; 
this end of the improved trumpet is, on 
‘the contrary, expanded,—so that, when 
applied to the side of the head, the whole 
ear is included, and remains uncompressed, 
whereby distinct hearing, through these 
tubes, is greatly promoted. 
Dr. Bryce’s Test of Perfect Vaccination, 
now in yery general use in Scotland, con- 
sists in vaccinating the other arm with 
matter taken from the pustule on the arm 
first inoculated. 
Animal Dye.—A kind of grass, called 
Polygonum minus, abounds in the deserts of 
Ukraine. Towards the end of the month 
of June, this grass is torn up by the roots, 
which are covered with maggots, of an oval 
shape, that become indurated as soon as 
they are exposed to the air: they are 
sold by the spoonful to merchants, are 
pounded, and the water in which they 
are steeped, with a little alum, assumes 
the colour of the most beautiful crim- 
son. The wives of the Cossacks dye 
their thread with them; and the Russian 
merchants buy them for their wives to 
paint their faces with. The Armenians 
sell large quantities in dyeing their silks, 
their moroccos, the tails and manes of their 
horses, and their own hair, beards and 
nails. The name of coccus Polonorwm has 
been giveu to these maggots. 
Oil of Mace.—Some experiments made 
on oil of mace, by Mr. William Bollaert, 
communicated to the Journal of Science 
(January 1825), have proved that this oil 
contains a peculiar principle, detected by 
_ repeated distillations of essential oil, ob- 
tained from the common oil of mace. It is 
of a whitish appearance and crystalline tex- 
ture, perfectly insoluble in water, insipid, 
inodorous, and very fusible. Its boiling 
point is about 600°, at which temperature 
it may be distilled without much decompo- 
sition. The oil of mace affords about one- 
half of this peculiar principle. 
Benxoic Acid. —Mr. Bollaert has detected 
the presence of benzoic acid in Botany Bay 
gum, in the proportion of about six per 
cent.; and in oil of cassia—a deposit from 
‘which formed crystalline filaments, consist- 
ing almost entirely of benzoic acid. 
‘Spirit of Philosophical Discovery. 
[April I, 
Addenda and Desiderata. 
Barometrical Presswe. —The maximum 
pressure, in 1824, was one-quarter of an 
inch higher than in 1823; the minimum 
pressure, one-fifth of an inch less. -The 
mean pressure was goo inch less, but 
agreeing, within 3°000, with that of the 
last ten years. We 
Temperature. — The mean temperature 
of the external air, a few feet from the 
ground, was, in 1824, nearly one degree 
and a half more than in 1823, and nearly 
one quarter degree more than in the 
preceding eight years. 
Rail-Roads.—On a well-made road 2 
good horse will draw a load of one ton, ina 
cart weighing 7 cwt., at the rate of two 
miles an hour. On a rail-road of the best 
formation, at the same rate of travelling, 
a horse will draw 15 ton, including the ve- . 
hicle. Thus, then, this computation refer- 
ring, only, to a velocity of two miles an hour, 
the effect produced by the draught of a 
single horse is ten times as great on a rail- 
road as upon one of ordinary construction. 
But the laws of friction, as established by 
Coulomb and Vince, present results that 
will, perhaps, shock the faith of practical 
men, though the principle from which they 
flow is admitted, by all scientific mecha- 
nicians; We allude immediately to this— 
The friction of rolling and sliding bodies, 
nearly but not precisely, follows the same 
law as velocity; and that law is, that 
the friction is the same for all velocities. 
Crystallization.—Little is known of the 
forces and influences which cause the fo1ma- 
tion, and still less of those that produce, the 
diversity of forms of crystals. This is a sub- 
ject which has afforded scope for, and baffled 
the diligent research of many ; and even the 
learned Haiiy has been unable satisfactorily 
to explain the matter. Theories have been 
framed, and others may be: yet, to use the 
words of Mr. Brooke, in a paper, (printed 
in the 23d number of the Edinb. Phil. 
Journ. ), “ there does not appear to be any 
hypothesis capable of accounting for the 
variety of forms under which crystals pre- 
sent themselves ;’’ and the observations of 
Sir H. Davy (in the Phil. Tr. for 1822) 
“ render it not improbable that natural crys- 
tals are formed under very different states, 
both of pressure and temperature.” The 
paper alluded to contains many very accu- 
rate details of experiments, tending to eluci- 
date this subject ; but still it must, perhaps, 
remain involved in obscurity; and though 
the progress of discovery has been so rapid 
latterly, that it is hazardous to venture to 
predict its boundary in any direction, we 
cannot but think that the Jaws of crystalliza- 
tion will be great and lasting pUZZLERS to 
many an accurate and experimental chemist 
yet to rise, and illuminate (in many things) 
“* this fair orb.” 
Artificial Leather. — Dr. Bernhard, of 
Larris, 
