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A bicycle is a two wheeled vehicle driven by the riders feet pushing on cranks or pedals. A common misconception is that the earliest form of bicycle was the dandy-horse, which was pushed along by the rider's feet. However, while both the dandy-horse and the later bicycle are both velocipedes, the dandy-horse is not propelled by cranks.
The first bicycle was introduced to England from France in 1868, and comprised two solid wheels of equal size fitted to a frame, much like a modern bicycle in appearance, with a saddle fitted in the centre and propelled by cranks attached to the front wheel. This vehicle provided such a bumpy ride to the rider that it became popularly known as 'the bone-shaker'. Later came the Penny-Farthing with pedals fixed to the large front wheel which was made large to achieve high speeds. Later still, around 1895, came the safety bicycle with pedals driving the rear wheel by way of a chain, and the rider sitting upon a saddle set back from the front wheel so as to reduce the chances of falling forwards over the handlebars, from this developed the Raleigh bicycle design of 1900 which forms the basis of the modern bicycle. In 1888 the two-person tandem bicycle was invented.
In 1906 it was reported that speeds of 50 mph were attained on a bicycle. Around the same time, slightly earlier, the motorised bicycle (motorcycle or motorbike) was invented.
A typical bicycle is comprised of several parts. The principal and essential being: the frame, front forks, wheels, pedals, saddle, handlebars, chain and brakes. The largest part of the bicycle is the frame, and these vary in design depending upon the specialised intention of the bicycle.
A frame for a BMX bicycle being small, heavily braced and made of aluminium. The frame for BMX xyxling needs to be strong so as to endure the stresses of the bumpy ride, and the saddle low as competitors never sit down during a competition and as such they need space to sprint and jump with ease.
Cross-Country cycle frames are generally made of aluminium and carbon-fibre so as to be light weight. They are relatively small frames to allow quick and easy mounting and dismounting off road, and strong to endure off-road bumpy conditions. The smaller frames are often compensated for by having a longer seat post to allow a normal height saddle position.
The cycle speedway bicycle frame is designed primarily for strength, and as such is typically made from steel or aluminium.
Road racing bicycle frames are designed to be light and stiff. Traditionally they ewre made of steel, but by the start of the 21st century carbon fibre was being used for the more expensive models as this offered the same stiffness at reduced weight. The design of the tubes also developed over time, tubes becoming of a larger diameter, but thinner walls, to allow the same stiffness with reduced weight.
Bicycles are fitted with various types of brake, the most popular being the calliper, cantilever, hydraulic or disc and the V brake. The most common form of brake found on leisure bicycles, is that form used also on road racing bicycles. The calliper brake. Calliper brakes are a very efficient means of rim braking and basically comprise two blocks of rubber or plastic which are squeezed onto the wheel rim when the brake lever is squeezed by the ride.
Cantilever brakes operate on the same principal as calliper brakes, but are of a slightly different design at the wheel end, offering increased clearance between the tyre and the brake pads and as such are frequently employed for cyclo-cross bicycles and mountain bikes.
The most efficient form of rim brake is the V brake. The V brake also offers the most clearance of any rim braking system, and is most often found on mountain bikes.
Hydraulic or disc brakes are the most efficient and powerful form of bicycle brake. They use the wheel hub to brake, rather than the rim. Disc brakes offer the most clearance, and as such are used on mountain bikes, but are also expensive to fit and maintain.
Bicycle wheels are generally of one of three types. The most common and traitional bicycle wheel is the spoked wheel, comprising a rim connected to the central bub by a series of thin metal rods known as spokes. Spoked wheels are light in weight. Less common than spoked wheels, but offering greater strength and durability at the expense of weight are mag wheels which comprise a rim attached to the hub by a few, thick solid plastic bars. Solid wheels, also known as disc wheels, are made from composite material or carbon fibre are very strong, stiff, aerodynamic and very expensive. They are rarely used except as rear wheels in time-trialing and track racing.
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An eclipse is the interception or obscuration of the light of the sun, moon or other heavenly body by the intervention of another and non-luminous heavenly body. Stars and planets may suffer eclipse, but the principal eclipses are those of the sun and the moon.
An Eclipse of the Moon is an obscuration of the light of the moon occasioned by an interposition of the earth between the sun and the moon; consequently, all eclipses of the moon happen at full moon; for it is only when the moon is on that side of the earth which is turned away from the sun, and directly opposite, that it can come within the earth's shadow. Further, the moon must at that time be in the same plane as the earth's shadow; that is, the plane of the ecliptic in which the latter always moves. But as the moon's orbit makes an angle of more than 5 degrees with the plane of the ecliptic, it frequently happens that though the moon is in opposition it does not come within the shadow of the earth.
An Eclipse of the Sun is an occultation of the whole or part of the face of the sun occasioned by an interposition of the moon between the earth and the sun; thus all eclipses of the sun happen at the time of new moon. As the earth is not always at the same distance from the moon, and as the moon is a comparatively small body, if an eclipse should happen when the earth is so far from the moon that the moon's shadow falls short of the earth, a spectator situated on the earth in a direct line between the centres of the sun and moon, would see a ring of light round the dark body of the moon; such an eclipse is called annular; when this happens there can be no total eclipse anywhere, because the moon's umbra does not reach the earth. An eclipse can never be annular longer than 12 minutes 24 seconds, nor total longer than 7 minutes 58 seconds; nor can the entire duration of an eclipse of the sun ever exceed 2 hours.
An eclipse of the sun begins on the western side of his disc and ends on the eastern; and an eclipse of the moon begins on the eastern side of her disc and ends on the western. The average number of eclipses in a year is four, two of the sun and two of the moon; and as the sun and moon are as long below the horizon of any particular place as they are above it, the average number of visible eclipses in a year is two, one of the sun and one of the moon.
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The Keeway Superlight 125 is a Chinese classic motorcycle manufactured since 2007. The Keeway Superlight 125 is powered by a single cylinder, four stroke, air cooled engine started by both an electric ignition and kisk start, and providing a top speed of 50 mph. The Keeway Superlight 125 has a disc brake on the front wheel and a drum brake on the rear wheel.
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A thaumatrope is a card or disc with two different figures drawn one each side. These images apparently merge when the card or disk is rotated rapidly. Thaumatropes are used to demonstrate the persistence of visual impressions.
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Chamomile (Chamaemelum nobile) is a perennial herb of the family Compositae with a short, much branched creeping rhizome, low-growing, creeping or ascending hairy stems and alternate, finely divided (two or three times pinnate) leaves with inrolled margins. The flowerheads are terminal and solitary and have conical, solid receptacles and either white, ligulate ray-florets and yellow tubular disc-florets or in some cultivated species only ligulate florets. The receptacle bears chaffy scales between the florets.
Chamomile is a mild sedative, and is used as a herbal tea for insomnia and mild pain relief.
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The common seal (Phoca vitulina) is the smaller of the two native British species of seal, about two metres in length, with the females smaller than the males. They have a rather rounded, disc-like face with a short snout and very variable colourings, the coat usually being some shade of grey or white with darker spots. The females give birth to the pups on land, but the pups can swim straight away. The adults dive well for fish, staying submerged for up to ten minutes.
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The daisy is a genus of hardy perennial herbs of the Compositae family. The solitary flowerheads have white to pinkish, ligulate ray-florets and yellow, tubular disc-florets that close in the evening and are very attractive to bees. The fruit is an oval, downy achene without a pappus.
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Echeneis is a genus of fishes, of the mackerel family Scomberidae, having a disc on the head by which the fish can attach itself firmly to a solid object. Echeneis Kemora is abundant in the Mediterranean.
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The Echinus (Sea-Urchins or Sea-Eggs) are a genus of marine animals, the type of an order (Echinoidea) of the class Phylum Echinodermata. The body is more or less globular and covered with a test or shell, often beset with movable spines. Locomotion is effected by a singular system of ainbulacra or 'tube-feet', which are distended with water, protruded through pores, and again retracted. The mouth is situated on the inferior surface, generally in the centre, is armed with calcareous teeth, and opens into a gullet conducting to a distinct stomach. The stomach has issue into a convoluted intestine which winds round the interior of the shell and terminates in a distinct anus. The anus varies in position, being sometimes on the apical disc and sometimes marginal. The Echinus esculentus and some other species are edible.
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The feather-star, (Comatula rosacea) is a beautiful crinoid star-fish occurring on the British coasts, consisting of a central body or disc, from which proceed five radiating arms, each dividing into two secondary branches, so that ultimately there are ten slender rays. Each arm is furnished on both sides with lateral processes so as to assume a feather-like appearance. It is fixed when young by a short stalk, but exists in a free condition in its adult state.
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The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
©1993 - 2009 The Probert Encyclopaedia
Southampton, United Kingdom
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