BURNING GLASS. 
hotionr of John Burmann ; a genus of the 
Hexandria Monosynia class and order. Na- 
tural order of Liliaceous Flowers. Corona- 
riae, Linnasus. Bromelias, Jussieu. Essen- 
tial character; calyx prismatic coloured, 
trifid; andes membranous; petals three; 
capsule three celled, straight; seeds mi- 
nute. There are but two species; of which 
B. disticha has the root composed wholly 
of capillary fibres, very small. The plant 
has the appearance of an anthericum ; root- 
leaves six, grass-like or ensiform, two inches 
long, quite entire ; stem upright, simple, a 
span and half in height, having six or seven 
small alternate leaves an inch long; two 
equal divaricating spikes, each composed of 
about nine flowers, terminate the stem; 
the flowers are sessile, in a single row; 
they are blue, very elegant, and do not fall 
off. It is a native of Ceylon. B. biflora, 
has strong fibrous roots, with several ob- 
long oval leaves arising from it, w'hich are 
smooth and entire, four or five inches long ; 
among these, springs the flower stem, six 
or eight inches high, terminating by blue 
flowers, growing together in each sheath. 
It is a native of Virginia and Carolina. 
BURN, in medicine and surgery, an in- 
jury received in any part of the body, ei- 
ther by fire itself, or by instruments put in 
a violent heat by the fire. See Surgery. 
BURNING-ghm, a convex or concave 
glass, commonly spherical, which being ex- 
posed directly to the sun, collects all the 
rays falling thereon into a very small space, 
called the focus ; where wood, or any other 
combustible matter being put, will be set 
on fire. See Optics. 
We have some extraordinary instances 
and surprizing accounts of prodigious effects 
of burning-glasses. Those made of reflect- 
ing mirrours are more powerful than those 
made with lenses, because the. rays from a 
mirrour are reflected all to one point 
nearly; whereas by a lens, they are re- 
fracted to different points, and are there- 
fore not so dense or ardent. The whiter 
also the metal or substance is, of which the 
mirrour is made, the stronger will be the 
effect. 
The most remarkable burning-glasses, or 
rather mirrours, among the ancients, were 
those of Archimedes and Proclus ; by the 
first of which the Roman ships, besieging 
Syracuse, according to the testimony of 
several writers, and by the other, the navy 
of Vitalian besieging Byzantium, were re- 
duced to ashes. Among the moderns, the 
burning mirrours of greatest eminence, are 
those of Villette, and Tschirnhausen, and 
the new complex one of M. de Buffon. 
That of M. de Villette, was three feet 
eleven inches in diameter, and its focal 
distance was three feet two inches. Its 
substance is a composition of tin, copper, 
and tin-glass. Some of its effects, as found 
by Dr. Harris and Dr. Desaguliers, are, 
that a silver sixpence melted in 7i" ; a King 
George’s halfpenny melted in 16 ", and ran 
in 31" ; tin melted in 3", and a diamond 
weighing 4 grains, lost |ths of its weight. 
That of M. de Buffon is a polyhedron, 
six feet broad, and as many high, consisting 
of 168 small mirrours, or flat pieces of look- 
ing-glass, each six inches square ; by means 
of which, with the faint rays of the sun in the 
month of March, he set on fire boards of 
beech wood at 150 feet distance. Besides, 
his machine has the conveniency of burning 
downwards, or horizontally, as one pleases ; 
each speculum being moveable, so as, by 
the means of three screws, to be set to a 
proper inclination for directing the rays 
towards any given point ; and it turns either 
in its greater focus, or in any nearer inter- 
val, which our common buniing-glasses 
cannot do, their focus being fixed and dc- 
tennined. M. de Buffon, at another time, 
burnt wood at the distance df 200 feet. 
He also melted tin and lead, at the distance 
of above 120 feet, and silver at 50. 
Mr. Parker, of Fleet-street, London, was 
induced, at an expense of upwards of 700/. 
to contrive and at length to complete a 
large transparent lens, that would serve 
the purpose of fusing and vitrifying such 
substances as resist the fires of ordinary 
furnaces, and more especially of applying 
heat in vacuo, and in other circumstances 
in which it cannot be applied by any other 
means. After directing his attention for 
several years to this object, and performing 
a great variety of experiments in the pro- 
secution of it, he at last succeeded in the 
construction of a lens, of flint-glass, three 
feet in diameter, which, when fixed in its 
frame, exposes a surface tw'o feet 8^ inches 
in the clear, without any other material im- 
perfection besides a disfigurement of one 
of the edges by a piece of the scoria of the 
mould, which unfortunately found its way 
into its substance. This lens was double 
convex, both side.s of which were a portion 
of a sphere of 18 feet radius. It is difficult 
to form an accurate estimate of the burning 
power of this lens ; inasmuch as it is next 
to impossible to discover what should be 
deducted for the loss of power, in conse- 
