378 BEAM. 
vtrens,—is a native of Jamaica, grows there to 
the height of about 40 feet, and was introduced 
to Great Britain about the middle of the 17th 
century.—A beautiful species, called the com- 
pound-leaved, Melia composiia, is a native of Ten- 
eriffe, grows to the height of 20 feet, and was 
introduced to Britain in 1810.—A recently dis- 
covered and half-hardy species, called the Aus- 
tralian, was introduced a few years ago from New 
Holland.—All the other introduced species are 
evergreen natives of India; and one of them bears 
the name of the Guinea Lilac.— Afiller.— Loudon. 
—Marshall—The Materia Medica of Hindostan. 
BEAM. A piece of wood, or of iron, used in 
supporting a weight, or resisting a pressure. The 
| general results of the strength of wood are given 
in our article StrenetH or Marertats. From ex- 
isting structures, it appears that security will be 
attained by limiting the weight borne by a tim- 
ber beam to one-fifth of that which would cause 
rupture by compression. Although the elasticity 
_ of timber is said not to be affected by a force 
| which is between one-fourth and one-third of 
_ that which causes rupture, still it is prudent not 
_ to submit it to so great a permanent strain. 
To determine the limits of the cross strain to 
which timber can be submitted with safety, it 
should be borne in mind, that the degree of flex- 
ure caused by the strain must not impair the 
elasticity of the fibres, so that when the strain is 
taken off the piece may regain its natural form. 
There are no special experiments from which this 
limit can be ascertained; but, from an examina- 
tion of existing structures, it seems that timber 
| may be exposed with entire safety to a cross 
strain equal to one-tenth of that which would 
cause rupture. 
When a vertical beam is pressed by a force at 
top, it has been ascertained by experiments, that 
if the length is greater than 8 or 10 times the 
| thickness, rupture will take place by the bend- 
| ing of the beam; and that when the length is 
| less than 8 times the thickness, the beam will 
yield by crushing. In all cases where the length 
is less than 20 times the thickness, the weight to 
be borne will be estimated from that by which 
rupture is caused by crushing the fibres. But as 
any slight lateral strain in addition to this would 
cause the beam to give way, this weight must be 
farther reduced, depending on the length of the 
beam. The experiments made to ascertain this 
reduction, indicate that, for wood, the weight 
borne should be reduced to the four-fifths, when 
the length is equal to 12 times the thickness; and 
| to one-half when it is 24 times the thickness. 
For cast-iron, the weight should be reduced to 
the two-thirds, when the length is 4 times the 
| thickness; to about the one-half, when it is 8 times 
the thickness ; and to the one-fifteenth, when it 
is 36 times the thickness. For forged iron, the 
| weight should be reduced to the five-eighths, when 
| the weight is 12 times the thickness; and to one- 
half, when it is 24 times the thickness. 
BEAN. 
The following are the medium crushing weights 
for a square inch of each of these materials, when 
the length is once or twice the thickness. 
Oak and Pine 4,000 Ibs. 
Forged iron 60,000 — 
Cast-iron 5 140,000 — 
Having ascertained the reduction of the crush- 
ing weight required by the length, the total per- 
manent weight borne should be only about one- 
tenth of this for wood, and between one-fourth 
and one-fifth for forged or for cast-iron. “The 
rule that is generally followed by practical men,” 
says Millington, “for determining the necessary 
strength and dimensions of a pillar or vertical 
support, is to take such of the experiments as 
have been before detailed as may suit the case, 
and to multiply the result given until it reaches 
the sought-for power, and then to take only one- 
fourth or one-fifth of that quantity to work upon. 
Thus, if a single square inch of brick is capable 
of supporting 562 lbs., two inches should support 
twice that weight, or 1,124 Ibs., and ten inches 
should support 5,620 Ibs., and so on; but instead 
of trusting the ten inches of brick to bear the 
5,620 lbs., only one-fourth or one-fifth of that 
load should be placed upon it; or if the whole 
load must be carried, the surface of brickwork 
should be extended to four or five times ten 
inches. This has always been deemed a safe 
rule, because it is merely making the strength to 
increase as the area, and then only using about 
a quarter of the strength given by thetrial. The 
reason for making so large a deduction is two- 
fold; first, to guard against imperfect workman- 
ship, and, secondly, against natural decay. By 
imperfect workmanship is meant the almost im- 
possibility, in practice, of getting heavy beams or 
pieces of stone to bear equally upon every part of 
the surface that is prepared to support them, 
arising from the difficulty in moving and placing 
heavy bodies, or from the support settling or 
sinking to a greater distance than was contem- 
plated, in consequence of receiving the new load, 
or its settling unequally in different parts. Thus 
a pier of brickwork containing 180 square inches 
of surface, might be built to support a burden of 
many thousand pounds, which it would be fully 
competent to bear, provided the weight was 
equally distributed over the whole surface. But 
in placing it, it might happen that the whole 
would rest upon three or four square inches, 
which, being incompetent to the load, would fail, 
and transfer it to another small part, equally in- 
competent to bear it, and thus the whole might 
fail.” 
BEAN,—botanically Haba. A well-known cul- 
tivated plant, of the vetch division of the legumi- 
nous family. It is cultivated in both the garden 
and the field, for the sake of its large, nutritious, 
dicotyledonous seeds; and is so universally known 
to our population, both urban and rural, as not 
to require any description. , Its flowers are of 
the butterfly kind, large, beautiful, and grate- 
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