An Encyclopedia of the History of Technology part 75 potx

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to record the singing voice. However, until the commercial pressing industry
began around 1900, multiple copies could only be made by using a bank of
machines, or copying from one machine to another.
Magnetic and optical recording and reproduction
Edison in 1878 and Tainter in 1885 had proposed magnetic recording, but it
was not until 1898 that Valdemar Poulsen invented a system for recording
on a steel wire: the telegraphone. One of the biggest advantages of a
magnetic-recording medium was its erasability, so that it could be used again
and again, particularly important in business applications such as dictating.
Poulsen also suggested magnetically coated tapes and discs in his patents, but
exploitation of these media had to wait until plastics were discovered and a
coating industry in place. In 1920 an Austrian, Pfleumer, developed a plastic
magnetic tape, but it was not until 1934 that magnetic recording tape was
first manufactured by BASF in Germany. After the war, largely due to the
enthusiasm of Bing Crosby, tape became the preferred medium for pre-
recording radio programmes. Tape became standard in recording studios
soon afterwards.
Another means of sound recording is optical, and it would not have been
surprising if Edison, one of the inventors of the motion picture, had hit upon
this means of adding sound. In fact Edison’s laboratory had been able to
synchronize film and discs in 1889, and Joseph Poliakoff, a Russian, patented a
Figure 15.3: Cylinder phonograph for recording and transcribing dictation; the
governor regulated the speed of the weight-driven ‘motor’.
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photoelectric system in 1900. Augustus Rosenberg patented a stereophonic
talking film system in 1911. However, none of these systems were
commercialized. In 1926, Warner Brothers tried to stimulate lagging interest in
its films by making synchronized-sound motion picture—‘talkies’. They chose

to use a sound-ondisc system, and contracts were awarded to Western Electric
and the Victor Talking Machine Company. The first picture to be released
under this system was Don Juan, but the big success—which spelled the end of
the silent film era—was The Jazz Singer (1927), starring Al Jolson. Warner
Brothers then installed disc-recording equipment in their studios, naming the
system Vita-phone. Also in 1927, the first commercially successful sound-on-
film system was marketed by Fox Movietone News. This used a variable
intensity method of modulating a light beam (the Aeo-light) to expose a track
on the side of the film negative.
Stereophonic sound and the long-playing record
In 1931, Alan D.Blumlein at EMI in the UK and the Bell Telephone
Laboratories in the US almost simultaneously brought out the first complete
stereophonic sound systems. Blumlein produced a reel of test film, but it was
not until 1942 that Walt Disney’s feature-length cartoon Fantasia brought stereo
to the public. In 1948, RCA and others developed a system for coating a strip
of magnetic oxide on 35mm film, which provided a higher dynamic range and
permitted re-recording. This became the standard method for providing sound
on amateur films—16mm, and later Super-8.
Also in 1948, Peter Goldmark, working at CBS Laboratories in the US,
invented the long-playing record (LP). This was a radical improvement of disc
recording. Previously, discs had been made of a rigid, composite material and
coated with shellac—if one was dropped, it cracked or broke—and even a 12-
inch-diameter disc could hold only four minutes of sound. The LP was
thinner, lighter and was made out of flexible vinyl plastic, which provided
much lower surface noise. Also, LPs could play almost thirty minutes of high-
fidelity music on a side, thanks to the invention of microgroove recording (100
grooves per cm instead of 36), and the slowing down of the rotational speed
(33 1/3rpm instead of 78). Almost at the same time, RCA brought out a rival
microgroove system using a smaller, 45rpm disc. However, its playing time was
about the same as the 12-inch 785—only long enough for singles of hit songs.

Even though the two incompatible systems confused the public, LP became a
success and in a few years 78rpm production was stopped forever.
In 1958, the 45–45 cutting system for stereo recording, originally invented
by Blumlein, became a world standard. This puts both channels in a single
micro-groove. The introduction of stereo recordings required the audiophile to
replace much of his equipment; he had to have a new, more compliant stylus,
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two matched amplifiers, and two loudspeakers. Despite this additional
complexity and expense, stereo hi-fi caught on quickly with the public.
Magnetic tape recording and reproduction
Also about this time, stereophonic reel-to-reel recorders using 1/4in-wide
magnetic tape became popular, because owners could record selections off
the air, and tape could play for hours without interruption. However, a
certain amount of manual dexterity was required to thread the tape through
the magnetic heads and drive mechanism (similar to the skill needed to
thread the film through an amateur movie projector). In the early 1960s,
RCA tried to market a cartridge tape, but it was not until 1963 that Philips
in the Netherlands hit upon the right production and marketing strategies to
make their compact cassette a worldwide standard for audio recording. It
took only a moment to snap a cassette into a recorder, and both were
miniaturized to such an extent that using batteries, they could be carried
about. One innovative marketing technique of Philips was to offer
manufacturing details and working drawings of their design free of charge to
all others willing to adhere to the standard. This was unheard-of in a world
where most firms tried to ensure that potential competitors were licensed
under their patents or locked out of the market. However, the great
advantage to customers of being certain that any cassette would work in any
recorder led to the explosive growth of the cassette industry.
A compact cassette is only 10×6.4×1.2cm (3.9×2.5×0.5in), yet, because its

tape speed is one-half or one-quarter that of 1/4in reel-to-reel, it can play up to
an hour on each side. Great improvements in the formulation of the tape
coating have been made, the original iron oxide being supplemented by
chromium dioxide and, recently, metal; and in 1967, Ray Dolby in the US
brought out his patented noise-reduction system. All these developments have
meant that cassette audio reproduction, in terms of extended frequency and
dynamic range, high signal-to-noise ratio and low distortion, approaches the
best of the older reel-to-reel systems. The compact cassette is a two-hub system,
a miniaturized version of reel-to reel; the tape never leaves the enclosure, but is
exposed only as it passes by the recording or playing heads.
A rival system, the Lear Jet Pack endless-loop tape cartridge, a one-hub
system, makes ingenious use of the principle of the Moebius strip; both
surfaces of the tape may be recorded and played without rewinding. Also,
instead of the four tracks of the compact cassette (which provide two stereo or
four monaural channels, but require turning the cassette over to use the other
side), the Lear Jet cartridge had eight tracks providing four parallel stereo
channels. It had its best market in automobiles during the 1960s and early
1970s, but the greater fidelity and reliability of the cassette players, and the
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advantages of a single system for both home and car use, proved decisive.
Then in 1979, Sony introduced its Walkman, play-only cassette machines
which were half the weight and a fifth the size of older cassette recorders. The
idea was to bring cassette listening through earphones to stroller and jogger;
not only would the earphones blot out noise and distraction, but the sound
would not disturb others. The Walkman was an immediate success, and much
imitated; by the mid-1980s, high-quality players were available only slightly
larger than the cassettes themselves.
Even this technology is now being challenged by another, even more
revolutionary audio system, the Compact Disc or CD (see p. 755).

RADIO AND RADAR
Radio waves
The notion of transmitting information without the use of wires must have
seemed to our ancestors only a hundred years ago to be magic. In England,
during the 1860s, James Clerk Maxwell developed analogies between Faraday’s
conception of electric and magnetic lines of force, and incompressible fluid flow.
In a brilliant series of papers published in 1861 and 1862, he presented a fully
developed theory of electromagnetism, based on Faraday’s field concept. In his
theory, Maxwell was able to explain all existing electromagnetic phenomena, and
to predict the transmission of electromagnetic waves.
Heinrich Hertz in Germany proved the existence of these waves in 1887,
using what was probably the first antenna, two metallic plates each attached to
a 30cm (12in) rod. The two rods were placed in line and balls attached to their
nearer ends, separated by a 7mm (1/4in) gap. When a spark crossed the gap, a
similar spark was generated in the microscopic gap of a 70cm (27.5in) diameter
loop of wire at the other side of the room.
In the 1890s, Edouard Branly in France observed an effect of Hertzian
waves on metal filings in a tube. The normally nonconducting filings became
conductive only when the waves were being generated. Branly called the tube
of filings a coherer; it was what is called today a rectifier, and became the first
practical detector of electromagnetic waves. In 1893, J.J.Thompson in the UK
published a book intended to be a sequel to Maxwell’s. In it he made the first
suggestion of propagating electromagnetic waves through hollow tubes. It is
interesting that Hertz’s original experiment and Thompson’s idea both dealt
with what has come to be called microwave radiation, the basis of radar,
satellite telecommunications, diathermy and the microwave oven.
Wilhelm Röntgen, a German, experimenting with a tube invented by W.
Crookes in 1878, discovered in 1895 what he called X-ray (X standing for the
unknown, as in algebra). A current passed through the Crookes tube caused a
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piece of paper coated with barium platinocyanide to fluoresce. Röntgen soon
started using photographic plates in his experiments, and in 1895 the first X-
ray of a human hand was made, clearly showing the underlying bone
structure; a year later, the first X-ray of a human skull was made.
Thus, before the turn of the century, the means to generate and detect a
large portion of the electromagnetic spectrum had been found, even if not well
understood (Röntgen eventually died from the effects of his X-rays). Micro-
waves were centimetres long, light waves a fraction of a micrometre, and X-
rays one ten-thousandth of a micrometre—a range of about eight orders of
magnitude (10
8
). The waves we call radio are longer than microwaves, ranging
over another seven orders of magnitude, from ultra-high frequency (UHF)
which are about 30cm (1ft) in wavelength, to extremely low frequency (ELF)
waves thousands of kilometres long.
Wireless telegraphy
In 1896 the first patent for wireless telegraphy, that is the transmission of
messages without wires, was granted to Guglielmo Marconi in the United
Kingdom. By the following year the Wireless Telegraph Company had been
formed to exploit the invention, and in 1899 the Marconi Wireless Company
of America was set up. American Marconi, as it was called for short, soon
began the manufacture of wireless equipment for commercial and military
markets. In 1904, Alexander Fleming patented a two-electrode valve in the
United Kingdom. The invention was based on his observations of the 1884
Edison effect, in which a one-way flow of electricity (rectification of alternating
current) occurred when a metal plate was sealed inside a carbon-filament lamp.
Although Marconi’s original invention was designed for fixed (point-to-
point) and ship-to-shore message communication, the idea of wireless as a one-
way medium to transmit speech to many people—broadcasting—was quick to

follow. On Christman Eve 1906, Reginald Fessenden made the first
documented broadcast of speech and music from Brant Rock, Massachusetts.
His transmitter was a 1kW, 50Hz alternator built by the General Electric
Company in Schenectady, NY, under the direction of E.F.W.Alexanderson.
The signal was received clearly in many locations and even on ships at sea.
Lee de Forest made some experimental broadcasts from New York in 1907
and from Paris in 1910, but his 500W arc transmitters were inherently noisy.
However in 1906 one of his associates, General Henry H.C.Dunwoody,
patented a solid-state detector using the newly invented material
carborundum. These crystal detectors soon became the heart of early radio
receivers. Used with headphones which drew very little power, crystal sets
had the great advantage of not requiring any external source of electricity. In
1906, de Forest applied for a patent for a 3-electrode tube which he named
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the Audion. It was first though of as a device to amplify weak currents, but
de Forest soon extended the patent application to include detection. The
additional electrode greatly extended applications of what came to be called,
generically, thermionic valves; unfortunately, like many other inventions of
commercial importance, the triode patent led to extensive and bitter litigation
between de Forest and Fleming.
Early radio receivers were mostly constructed by amateurs who could make
their own components. They required large outdoor antennas (aerials) and the
use of headphones; in operation, locating and retaining the signal of a
broadcasting station (tuning in) demanded skill and patience. In 1917, Lucien
Lévy in France patented a superheterodyne circuit, which made tuning much
easier, reduced power requirements and simplified receiver construction.
Radio broadcasting
Marconi’s Wireless Telegraph Company first broadcast daily concerts from
Chelmsford, Essex, between 23 February and 6 March 1920. The transmitter

had a power of 15kW, and used an antenna strung between two 137m (450ft)
masts; programmes were picked up as far away as 2400km (1500 miles). On
15 June 1920 a concert by the celebrated Dame Nellie Melba was broadcast on
2800 metres (equivalent to 107kHz), with a power of 15kW; and on 14
November 1922 the British Broadcasting Company began a daily programme.
Educational broadcasting also was pioneered in the UK, beginning on 4 April
1924. Fifty years later, the British Broadcasting Corporation (BBC) was
providing more than 3100 broadcasts a year to schools, and 500 for further
education.
Broadcasting has a unique advantage over other communication media—its
messages are carried without any physical link between sender and receivers.
Unlike newspapers, magazines and the post, no rails, roads or vehicles are
needed to carry messages, resulting in large savings of time and expense.
Unlike the telegraph or telephone, no wires need be laid, so radio messages
can reach the remotest and most inaccessible locations, including ship at sea
and aircraft.
In the United States, the first organization to receive a radio licence
specifically for broadcasting was KDKA, a Westinghouse station in Pittsburgh.
Their first broadcast, on 2 November 1920, announced the results of the
Harding-Cox election. The first radio advertisement was bought by American
Telephone and Telegraph and broadcast over WEAF, New York, on 28 August
1922; the following year, the first radio network was created, between New
York and Boston.
Without government involvement, the spread of radio broadcasting in the
United States was unconstrained during the 1920s. Whereas in 1921 there
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were only two stations officially on the air, by 1925 there were more than 500
(not including thousands of very low-power, unauthorized do-it-yourself
stations). The first frequency assignment in the US was on 830kHz; by 1925

the spectrum from 550 to 1,350kHz was allocated exclusively to AM
(amplitude modulation) broadcasting, which is also called medium wave
(MW). In 1922, George Front in the US installed a radio in his Model T Ford;
and in 1927 the first product designed for automobile use, the Philco
Transitone, was introduced. Today probably more radio listening is done in
cars than in all other locations.
Radio stations added more and more power to reach larger audiences, with
some stations exceeding a million watts before government regulation brought
some order to the scene. For example, broadcasts of one Cleveland station
electrified nearby fences and provided free lighting for many households in the
neighbourhood; and some people who had tooth fillings even claimed that
they could hear (but could not turn off) the broadcasts—the filling acting as a
rectifier, and the programmes being heard by bone conduction, apparently.
Stations even interfered with each other on opposite sides of the continent, and
frequency and power regulation became essential. In any case, advances in
technology made unlimited power unnecessary to reach vast audiences: radio
stations became linked into networks via leased telephone lines.
In 1933, Edwin Armstrong in the US patented his FM (frequency modulation)
radio system and in 1938, General Electric installed the first FM broadcasting
station. In contrast to AM, FM is noise-free and uses a much greater band width,
so it became the preferred method for broadcasting high-fidelity music and
eventually stereophonic sound; on the other hand, because the channels assigned
to FM are in the very high frequency (VHF) band, signal reception is limited to
line-of-sight. Whereas listeners with ordinary AM sets often picked up stations
from overseas, particularly at night when their signals bounced off an expanded
ionosphere, FM waves penetrated and were lost in space.
Many other improvements were made in radio broadcasting and receiver
construction, but not until after the Second World War did components
became small enough to make truly portable radios. The invention of the
transistor in 1948 made such miniaturization possible, and the first transistor

radio appeared in 1955. During the next decades, prices dropped from
hundred of dollars to about $10 for the simplest sets, and ‘transistors’, as they
are called for short, have become ubiquitous, perhaps the product owned by
more individuals than any other in the world.
Radar
In 1924, Sir Edward Appleton and M.F.Barnett in the UK found that they
could bounce radio waves off the ionosphere, the existence of which had been
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hypothesized by Oliver Heaviside in the UK and Arthur Kennelly in the US
in 1901. A year later, Gregory Breit and Merle A. Tuve were the first to use a
pulse technique in similar experiments. During the next ten years, the US and
several European countries experimented with radio waves to detect aircraft
and ships at sea. In 1933, A.H.Taylor, L.C.Young and L.A.Hyland in the US
applied for a patent for a radio detection system, as did Henri Guton in France
the next year. However, for the next decade, research became shrouded in
wartime secrecy.
In 1935 in the UK, a committee headed by Sir Henry Tizard was set up to
investigate military applications of radio waves, and in that year Sir Robert
Watson-Watt with six assistants developed the first practical radar (Radio
Detection and Ranging) equipment for the detection of aircraft. Both the Allies
and the Axis powers had radar during the Second World War, but its most
dramatic role was during the Battle of Britain in 1940, when early-warning
radar gave the Royal Air Force a critical tactical advantage. Since the war, it
has become essential not only for a host of military purposes, but also for
civilian air traffic control.
Radar operates by sending out pulses of radio energy, a tiny portion of
which is reflected by objects in its path and picked up by highly directional
antennas. The range of such objects can be calculated automatically from the
difference in time between transmitted and received pulses. Microwave

frequencies work best; early-warning radars use 10m wavelengths, positional
radars 1.5m, and high-re solution systems wavelengths down to 10cm.
In 1933, Karl G.Jansky of the Bell Telephone Laboratories discovered that
radio waves were being generated by stars. He used a 30m (100ft) long
rotatable short-wave antenna. This began a new era in astronomy—radio
astronomy—which has greatly expanded our knowledge of star creation and
life processes, and has detected many stars invisible to light telescopes.
Immense dishes are used for this purpose, the largest being one in Puerto Rico,
with a diameter of 3km (1 3/4 miles), which is capable of detecting phenomena
out to 15,000 million light-years away.
PHOTOGRAPHY
In 1725, Johann Heinrich Schultz, a German physician and professor, was
trying to make a phosphorescent material by mixing chalk with nitric acid
containing dissolved silver. He observed that sunlight turned the mixture
black, and realized that he had a photosensitive material (even though he did
not use this term). He made photographic impressions of words and shapes cut
out of paper and placed against a bottle of the solution, but although he
published his discovery in 1727, he never made the image permanent—one
shake of the solution and it was gone forever.
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Tiphaigne de la Roche, in his sceince-fiction novel Giphantie (1760),
prophesied the ‘sun picture’: a canvas could be coated with ‘a most subtle
matter, very viscous and proper to harden and dry’, which when held before
an object to be painted would retain its image. He even had the notion of
present-day snapshot photography: ‘This impression…is made the first
instant… [and the canvas] is immediately carried away into some dark place an
hour after the subtle matter dries, and you have a picture… [which] cannot
be…damaged by time.’
Optics

Alhazen of Basra, a tenth-century Arab mathematician and scientist, observed
the inverted image of a sunny landscape on the wall of a darkened tent. He
realized that the critical element was a small hole in the tent material, and
made use of the discovery to observe eclipses of the sun. This was the first
recorded instance of what came to be called the camera obscura (dark room).
It might be thought that lenses, and especially the convergent (or convex)
lens and its focusing properties, would have been discovered far back in
antiquity. Glass vessels have come down to us from civilizations which
flourished several thousand years BC, such as the Egyptians. However, the
earliest recorded use of glass globes (probably filled with water) to kindle fires
is that of Lactantius, about AD 300. Lenses may be made out of many
substances as long as they are clear, that is, do not absorb much light: Arctic
explorers have astonished their Eskimo hosts by using blocks of clear ice cut in
the form of lenses to start fires. More recently, cast ice lenses have been used in
place of glass lenses in cameras, and provide a good, if soft-focus, image.
All the lenses so far described are simple convex ones. Only with the
development of optical science, and in particular the compound lens, have we
been able to approach the theoretical limits of optical magnification. It was
found that by using different curvatures and types of glass, and in particular by
setting several lenses a distance apart in blackened tubes, magnification could
be increased without worsening distortion. Almost all modern optical
instruments except simple magnifiers and spectacle lenses use such compound
lenses. Apparently, Johannes (or Hans) Lippershey in the Netherlands made a
crude telescope using two lenses in 1608, and Galileo constructed his own
upon hearing about it the following year. These devices were actually opera
glasses, using a convex objective and concave eyepiece, but with such
instruments Galileo made observations which revolutionized astronomy. Dutch
spectacle-makers are also supposed to have made the first microscopes, about
1590. An ton von Leeuwenhoek brought the single-lens magnifier to such
perfection that he was able to observe single-celled organisms for the first time.

However, the use of two lenses for microscopy seems not to have been
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accomplished until the mid-1600s, when Robert Hooke in England built the
first compound microscope.
Another precursor of photography was psychological; men began to see the
natural world as it really is, and not filtered through the mind of Aristotle. In
Italy and the Low Countries, artists studied the interplay of light with objects,
but up until the fifteenth century, drawings of three-dimensional objects looked
flat. About 1420, Filippo Brunelleschi discovered perspective. Brunelleschi
assumed that objects are perceived as a cone of rays proceeding from the eye;
he imagined a plane just in front of and at right angles to the eye on which he
could ‘project’ an image. The camera obscura, which essentially does this
projection optically for the artist, did not come into use as a drawing aid until
late in the sixteenth century. The Dutch mathematician Rainer Gemma-Frisius
published an illustration of a camera obscura used to register the solar eclipse
of 24 January 1544, and Girolamo Cardano of Milan reported that a convex
lens placed in an opening of a darkened room would produce a bright, sharp
image. Up until that time, the clearest images had been produced by a hole of
small diameter, which gives a dim, somewhat soft, but wide-angle view.
Attempts to brighten the image by widening the aperture blurred the image
severely; only a convex lens—probably invented in Europe around the
thirteenth century—can provide images which are both sharp and bright.
The development of optics flourished in the sixteenth century with Kepler
and Galileo, and the artist’s camera obscura was soon reduced in size to a table,
and then to a box. Johann Zahn invented the reflex camera obscura in 1685,
using a mirror angled at 45° to reflect and invert the image on to a horizontal
sheet of frosted glass. It was a great convenience to artists to be able to observe
and trace an image which was right side up and in a horizontal plane.
In 1796, Tom Wedgwood, a son of the potter Josiah Wedgwood, was

experimenting with silver salts to record images of botanical and insect
specimens. However, he had no means to fix the images, which grew blacker
at each examination until soon they were gone. If he had learned to fix them
with ammonia or salt, he might have been the inventor of photography, but
this achievement had to wait until the following century.
The invention of photography
Nicéphore Niepce made the world’s first true photograph of a scene in 1826,
in St-Loup-de-Varennes, France. (However, a monument put up by the town
claims 1822.) His original interest was in improving lithography, which had
been invented in 1796 by Alois Senefelder (see p. 678). In 1814 Niepce
substituted a tin sheet for the heavy limestone from which lithography took its
name. He wanted light to do the work of transferring an existing engraving,
made transparent with oil, to the sheet. He tried a varnish made of bitumen of