History of the telephone

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Actor portraying Alexander Graham Bell in a 1926 silent film. The single-port design required the user to alternately speak into and then listen through the same hole.

This history of the telephone chronicles the development of the electrical telephone, and includes a brief review of its earlier predecessors.

Telephone prehistory[edit]

Mechanical devices[edit]

A 19th century acoustic 'tin can', or 'lover's' telephone

Before the invention of electromagnetic telephones, mechanical acoustic devices existed for transmitting speech and music over a distance greater than that of normal direct speech. The earliest mechanical telephones were based on sound transmission through pipes or other physical media.[1] The highly similar acoustic tin can telephone, or lover's phone, has been known for centuries. It connects two diaphragms with a taut string or wire, which transmits sound by mechanical vibrations from one to the other along the wire (and not by a modulated electrical current). The classic example is the children's toy made by connecting the bottoms of two paper cups, metal cans, or plastic bottles with tautly held string.[1][2]

Among the earliest known experiments were those conducted by the British physicist and polymath Robert Hooke from 1664 to 1685.[1][3] An acoustic string phone made in 1667 is attributed to him.[4]

For a short period of time acoustic telephones were marketed commercially as a niche competitor to the electrical telephone, as they preceded the latter's invention and didn't fall within the scope of its patent protection. When Alexander Graham Bell's telephone patent expired and many new telephone manufacturers began competing for customers, acoustic telephone makers quickly went out of business. Their maximum range was very limited, but hundreds of technical innovations, resulting in about 300 patents, increased their range to approximately a half mile (800 m) or more under ideal conditions.[2] An example of one such company was the Pulsion Telephone Supply Company created by Lemuel Mellett in Massachusetts, which designed its version in 1888 and deployed it on railroad right-of-ways.

Additionally, speaking tubes have long remained common, including a lengthy history within buildings and aboard ships, and can still be found in use today.[5]

Electrical devices[edit]

Main article: Electrical telegraph

The telephone emerged from the creation and successive improvements of the electrical telegraph. In 1804 Catalan polymath and scientist Francisco Salva Campillo constructed an electrochemical telegraph.[6] An electromagnetic telegraph was created by Baron Schilling in 1832. Carl Friedrich Gauß and Wilhelm Weber built another electromagnetic telegraph in 1833 in Göttingen.

Bell prototype telephone stamp
Centennial Issue of 1976

The first commercial electrical telegraph was constructed by Sir William Fothergill Cooke and entered use on the Great Western Railway in England. It ran for 13 mi (21 km) from Paddington station to West Drayton and came into operation on April 9, 1839.

Another electrical telegraph was independently developed and patented in the United States in 1837 by Samuel Morse. His assistant, Alfred Vail, developed the Morse code signaling alphabet with Morse. America's first telegram was sent by Morse on January 6, 1838, across 2 miles (3 km) of wiring.

During the second half of the 19th century inventors tried to find ways of sending multiple telegraph messages simultaneously over a single telegraph wire by using different modulated audio frequencies for each message. These inventors included Charles Bourseul, Thomas Edison, Elisha Gray, and Alexander Graham Bell. Their efforts to develop acoustic telegraphy in order to significantly reduce the cost of telegraph messages led directly to the invention of the telephone, the speaking telegraph.

Invention of the telephone[edit]

Credit for the invention of the electric telephone is frequently disputed, and new controversies over the issue have arisen from time-to-time. Charles Bourseul, Antonio Meucci, Johann Philipp Reis, Alexander Graham Bell, and Elisha Gray, amongst others, have all been credited with the telephone's invention. The early history of the telephone became and still remains a confusing morass of claims and counterclaims, which were not clarified by the huge mass of lawsuits to resolve the patent claims of many individuals and commercial competitors. The Bell and Edison patents, however, were commercially decisive, because they dominated telephone technology and were upheld by court decisions in the United States.

The modern telephone is the result of work of many people.[7] Alexander Graham Bell was, however, the first to patent the telephone, as an "apparatus for transmitting vocal or other sounds telegraphically". Bell has most often been credited as the inventor of the first practical telephone. However, in Germany Johann Philipp Reis is seen as a leading telephone pioneer who stopped only just short of a successful device, and as well the Italian-American inventor and businessman Antonio Meucci has been recognized by the U.S. House of Representatives for his contributory work on the telephone.[8] Several other controversies also surround the question of priority of invention for the telephone.

The Elisha Gray and Alexander Bell telephone controversy considers the question of whether Bell and Gray invented the telephone independently and, if not, whether Bell stole the invention from Gray. This controversy is narrower than the broader question of who deserves credit for inventing the telephone, for which there are several claimants.

The Canadian Parliamentary Motion on Alexander Graham Bell article reviews the controversial June 2002 United States House of Representatives resolution recognizing Meucci's contributions 'in' the invention of the telephone (not 'for' the invention of the telephone). The same resolution was not passed in the U.S. Senate. thus labeling the House resolution as "political rhetoric". A subsequent counter-motion was unanimously passed in Canada's Parliament 10 days later which declared Bell its inventor. This webpage examines critical aspects of both the parliamentary motion and the congressional resolution.

Invention of the telephone exchange[edit]

In the era of the electrical telegraph, post offices, railway stations, the more important governmental centers (ministries), stock exchanges, very few nationally distributed newspapers, the largest internationally important corporations and wealthy individuals were the principle users of such telegraphs.[9] Despite the fact that telephone devices existed before the invention of the telephone exchange, their success and economical operation would have been impossible on the same schema and structure of the contemporary telegraph. Prior to the invention of the telephone exchange switchboard, early telephones were hardwired to and communicated with only a single other telephone (such as from an individual's home to the person's business).

A telephone exchange is a telephone system located at service centers (central offices) responsible for a small geographic area that provided the switching or interconnection of two or more individual subscriber lines for calls made between them, rather than requiring direct lines between subscriber stations. This made it possible for subscribers to call each other at homes, businesses, or public spaces. These made telephony an available and comfortable communication tool for everyday use, and it gave the impetus for the creation of a whole new industrial sector.

The telephone exchange was an idea of the Hungarian engineer Tivadar Puskás (1844 - 1893) in 1876, while he was working for Thomas Edison on a telegraph exchange.[10][11][12][13] The first commercial telephone exchange in the world was opened at New Haven, Connecticut with 21 subscribers on January 28, 1878,[14] in a storefront of the Boardman Building in New Haven, Connecticut. George W. Coy designed and built the world's first switchboard for commercial use. Coy was inspired by Alexander Graham Bell's lecture at the Skiff Opera House in New Haven on April 27, 1877.[14]

In Bell's lecture, during which a three-way telephone connection with Hartford and Middletown was demonstrated, he first discussed the idea of a telephone exchange for the conduct of business and trade. On November 3, 1877, Coy applied for and received a franchise from the Bell Telephone Company for New Haven and Middlesex Counties. Coy, along with Herrick P. Frost and Walter Lewis, who provided the capital, established the District Telephone Company of New Haven on January 15, 1878.[14]

The switchboard built by Coy was, according to one source, constructed of "carriage bolts, handles from teapot lids and bustle wire." According to the company records, all the furnishings of the office, including the switchboard, were worth less than forty dollars. While the switchboard could connect as many as sixty-four customers, only two conversations could be handled simultaneously and six connections had to be made for each call.[14]

The District Telephone Company of New Haven went into operation with only twenty-one subscribers, who paid $1.50 per month. By February 21, 1878, however, when the first telephone directory was published by the company, fifty subscribers were listed. Most of these businesses and listings such as physicians, the police, and the post office; only eleven residences were listed, four of which were for persons associated with the company.[14]

The New Haven District Telephone Company grew quickly and was reorganized several times in its first years. By 1880, the company had the right from the Bell Telephone Company to service all of Connecticut and western Massachusetts. As it expanded, the company was first renamed Connecticut Telephone, and then Southern New England Telephone in 1882.[14] The site of the first telephone exchange was granted a designation as a National Historic Landmark on April 23, 1965. However it was withdrawn in 1973 in order to demolish the building and construct a parking garage.[14] In 1887 Puskás introduced the multiplex switchboard, that had an epochal significance in the further development of telephone exchange.[15]

Early telephone developments[edit]

The following is a brief summary of the history of the development of the telephone:

A French Gower telephone of 1912 at the Musée des Arts et Métiers in Paris
  • 1667: Robert Hooke invented a string telephone that conveyed sounds over an extended wire by mechanical vibrations. It was to be termed an 'acoustic' or 'mechanical' (non-electrical) telephone.
  • 1753: Charles Morrison proposes the idea that electricity can be used to transmit messages, by using different wires for each letter.[16]
  • 1844: Innocenzo Manzetti first mooted the idea of a “speaking telegraph” (telephone).
  • 1854: Charles Bourseul writes a memorandum on the principles of the telephone. (See the article: "Transmission électrique de la parole", L'Illustration, Paris, 26 August 1854.)
  • 1854: Antonio Meucci demonstrates an electric voice-operated device in New York; it is not clear what kind of device he demonstrated.
  • 1861: Philipp Reis constructs the first speech-transmitting telephone
  • December 28, 1871: Antonio Meucci files a patent caveat (No. 3353, a notice of intent to invent, but not a formal patent application) at the U.S. Patent Office for a device he named "Sound Telegraph".[17]
  • 1872: Elisha Gray establishes Western Electric Manufacturing Company.
  • July 1, 1875: Bell uses a bi-directional "gallows" telephone that was able to transmit "voicelike sounds", but not clear speech. Both the transmitter and the receiver were identical membrane electromagnet instruments.
  • 1875: Thomas Edison experiments with acoustic telegraphy and in November builds an electro-dynamic receiver, but does not exploit it.
  • 1875: Hungarian Tivadar Puskas (the inventor of telephone exchange) arrived in the USA.
  • April 6, 1875: Bell's U.S. Patent 161,739 "Transmitters and Receivers for Electric Telegraphs" is granted. This uses multiple vibrating steel reeds in make-break circuits, and the concept of multiplexed frequencies.
  • January 20, 1876: Bell signs and notarizes his patent application for the telephone.
  • February 11, 1876: Elisha Gray designs a liquid transmitter for use with a telephone, but does not build one.
  • March 7, 1876: Bell's U.S. patent No. 174,465 for the telephone is granted.
  • March 10, 1876: Bell transmits the sentence: "Mr. Watson, come here! I want to see you!" using a liquid transmitter and an electromagnetic receiver.
  • January 30, 1877: Bell's U.S. patent No. 186,787 is granted for an electromagnetic telephone using permanent magnets, iron diaphragms, and a call bell.
  • April 27, 1877: Edison files for a patent on a carbon (graphite) transmitter. Patent No. 474,230 was granted on May 3, 1892, after a 15-year delay because of litigation. Edison was granted patent No. 222,390 for a carbon granules transmitter in 1879.
  • 1877: The first experimental Telephone Exchange in Boston.
  • 1877: First long-distance telephone line
  • January 28, 1878: The first commercial telephone exchange opened in New Haven, Connecticut.
  • 1887: Tivadar Puskás introduced the multiplex switchboard.
  • 1915: First U.S. coast-to-coast long-distance telephone call, ceremonially inaugurated by A.G. Bell in New York City and his former assistant Thomas Augustus Watson in San Francisco, California.

Early commercial instruments[edit]

Early telephones were technically diverse. Some used liquid transmitters which soon went out of use. Some were dynamic: their diaphragms vibrated a coil of wire in the field of a permanent magnet or vice versa. This kind survived in small numbers through the 20th century in military and maritime applications where its ability to create its own electrical power was crucial. Most, however, used Edison/Berliner carbon transmitters, which were much louder than the other kinds, even though they required induction coils, actually acting as impedance matching transformers to make it compatible to the line impedance. The Edison patents kept the Bell monopoly viable into the 20th century, by which time telephone networks were more important than the instrument.

Early telephones were locally powered, using a dynamic transmitter or else powering the transmitter with a local battery. One of the jobs of outside plant personnel was to visit each telephone periodically to inspect the battery. During the 20th century, "common battery" operation came to dominate, powered by "talk battery" from the telephone exchange over the same wires that carried the voice signals. Late in the century, wireless handsets brought a revival of local battery power.

The earliest telephones had only one wire for both transmitting and receiving of audio, and used a ground return path, as was found in telegraph systems. The earliest dynamic telephones also had only one opening for sound, and the user alternately listened and spoke (rather, shouted) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but also more expensive.

Historical marker commemorating the first telephone central office in New York State (1878)

At first, the benefits of a switchboard exchange were not exploited. Instead, telephones were leased in pairs to the subscriber, for example one for his home and one for his shop, who must arrange with telegraph contractors to construct a line between them. Users who wanted the ability to speak to three or four different shops, suppliers etc. would obtain and set up three or four pairs of telephones. Western Union, already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco, and Bell was not slow in appreciating the potential.

Signaling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator, by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell, first operated over a second wire and later with the same wire using a condenser. Telephones connected to the earliest Strowger automatic exchanges had seven wires, one for the knife switch, one for each telegraph key, one for the bell, one for the push button and two for speaking.

Rural and other telephones that were not on a common battery exchange had hand cranked "magneto" generator to produce an alternating current to ring the bells of other telephones on the line and to alert the exchange operator.

In 1877 and 1878, Edison invented and developed the carbon microphone used in all telephones along with the Bell receiver until the 1980s. After protracted patent litigation, a federal court ruled in 1892 that Edison and not Emile Berliner was the inventor of the carbon microphone. The carbon microphone was also used in radio broadcasting and public address work through the 1920s.

1896 Telephone (Sweden)

In the 1890s a new smaller style of telephone was introduced, the candlestick telephone, packaged in three parts. The transmitter stood on a stand, known as a "candlestick" for its shape, hence the name. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook." Previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user was less likely to leave the phone "off the hook". In phones connected to magneto exchanges, the bell, induction coil, battery, and magneto were in a separate bell box called a "ringer box." In phones connected to common battery exchanges, the ringer box was installed under a desk, or other out of the way place, since it did not need a battery or magneto.

Cradle designs were also used at this time, having a handle with the receiver and transmitter attached, separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular.

Disadvantages of single wire operation such as crosstalk and hum from nearby AC power wires had already led to the use of twisted pairs and, for long distance telephones, four-wire circuits. Users at the beginning of the 20th century did not place long distance calls from their own telephones but made an appointment to use a special sound proofed long distance telephone booth furnished with the latest technology.

Around 1893, the country leading the world in telephones per 100 persons (teledensity) was Sweden with 0.55 in the whole country but 4 in Stockholm (10,000 out of a total of 27,658 subscribers).[18] This compares with 0.4 in USA for that year.[19] Telephone service in Sweden developed through a variety of institutional forms: the International Bell Telephone Company (a U.S. multinational), town and village co-operatives, the General Telephone Company of Stockholm (a Swedish private company), and the Swedish Telegraph Department (part of the Swedish government). Since Stockholm consists of islands, telephone service offered relatively large advantages, but had to use submarine cables extensively. Competition between Bell Telephone and General Telephone, and later between General Telephone and the Swedish Telegraph Dept., was intense.

In 1893, the U.S. was considerably behind Sweden, New Zealand, Switzerland, and Norway in teledensity. The U.S. rose to world leadership in teledensity with the rise of many independent telephone companies after the Bell patents expired in 1893 and 1894.

20th century developments[edit]

Old Receiver schematic, c.1906
A German rotary telephone, the W48
Top of cellular telephone tower

By 1904 over three million phones in the U.S.[20] were connected by manual switchboard exchanges. By 1914, the U.S. was the world leader in telephone density and had more than twice the teledensity of Sweden, New Zealand, Switzerland, and Norway. The relatively good performance of the U.S. occurred despite competing telephone networks not interconnecting.[21]

What turned out to be the most popular and longest lasting physical style of telephone was introduced in the early 20th century, including Bell's model 102 telephone. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use were placed in a cradle in the base unit. The circuit diagram[22] of the model 102 shows the direct connection of the receiver to the line, while the transmitter was induction coupled, with energy supplied by a local battery. The coupling transformer, battery, and ringer were in a separate enclosure from the desk set. The rotary dial in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1 to 10 times for each digit, and the hook switch (in the center of the circuit diagram) permanently disconnected the line and the transmitter battery while the handset was on the cradle.

Starting in the 1930s, the base of the telephone also enclosed its bell and induction coil, obviating a separate ringer box. Power was supplied to each subscriber line by central office batteries instead of the user's local battery which required periodic service. For the next half century, the network behind the telephone grew progressively larger and much more efficient, and after the rotary dial was added the instrument itself changed little until Touch-Tone signaling started replacing the rotary dial in the 1960s.

The history of mobile phones can be traced back to two-way radios permanently installed in vehicles such as taxicabs, police cruisers, railroad trains, and the like. Later versions such as the so-called transportables or "bag phones" were equipped with a cigarette lighter plug so that they could also be carried, and thus could be used as either mobile two-way radios or as portable phones by being patched into the telephone network.

In December 1947, Bell Labs engineers Douglas H. Ring and W. Rae Young proposed hexagonal cell transmissions for mobile phones.[23] Philip T. Porter, also of Bell Labs, proposed that the cell towers be at the corners of the hexagons rather than the centers and have directional antennas that would transmit/receive in 3 directions (see picture at right) into 3 adjacent hexagon cells.[24][25] The technology did not exist then and the radio frequencies had not yet been allocated. Cellular technology was undeveloped until the 1960s, when Richard H. Frenkiel and Joel S. Engel of Bell Labs developed the electronics.

On April 3, 1973 Motorola manager Martin Cooper placed a cellular phone call (in front of reporters) to Dr. Joel S. Engel, head of research at AT&T's Bell Labs. This began the era of the handheld cellular mobile phone.

Meanwhile the 1956 inauguration of the TAT-1 cable and later international direct dialing were important steps in knitting together the various continental telephone networks into a global network.

Cable television companies began to use their fast-developing cable networks, with ducting under the streets of the United Kingdom, in the late 1980s, to provide telephony services in association with major telephone companies. One of the early cable operators in the UK, Cable London, connected its first cable telephone customer in about 1990.

Women's usage in the 20th century[edit]

The telephone was instrumental to modernization and labour. It aided in the development of suburbs and the separation of homes and businesses, but also became the reason for the separation between women occupying the private sphere and men in the public sphere.[26] This would continue to isolate women and the home.

Women were regarded as the most frequent users of the telephone. As a means of liberation, it enabled women to work in the telecommunications sector as receptionists and operators. The autonomy was celebrated as women were able to develop new relationships and nurture pre-existing ones in their private lives. Social relations are essential in the access and usage of telephone networks.

Both historically and presently, women are predominantly responsible for the phone calls that bridge the public and private sphere, such as calls regarding doctor’s appointments and meetings.[27] This emphasizes the telephone’s impact on the social lives of women in the domestic sphere, reducing both isolation and insecurity.

21st century developments[edit]

See also: IP telephony

Internet Protocol (IP) telephony, also known as Internet telephony or Voice over Internet Protocol (VoIP), is a disruptive technology that is rapidly gaining ground against traditional telephone network technologies. In Japan and South Korea up to 10% of subscribers switched to this type of telephone service as of January 2005.

IP telephony uses a broadband Internet service to transmit conversations as data packets. In addition to replacing the traditional plain old telephone service (POTS) systems, IP telephony also competes with mobile phone networks by offering free or lower cost service via WiFi hotspots. VoIP is also used on private wireless networks which may or may not have a connection to the outside telephone network.

See also[edit]

References[edit]

This article includes text from Withdrawal of National Historic Landmark Designation: Site of the First Telephone Exchange, New Haven, New Haven County, Connecticut[dead link], by the United States National Park Service, a work in the public domain.
  1. ^ a b c McVeigh, Daniel P. An Early History of the Telephone: 1664-1866: Robert Hooke's Acoustic Experiments and Acoustic Inventions, Columbia University website. Retrieved January 15, 2013. This work in turn cites:
    • Richard Waller and edited by R.T. Gunther. "The Postthumous Works of Robert Hooke, M.D., S.R.S. 1705. Reprinted in R.T. Gunther's "Early Science In Oxford", Vol. 6, p. 185, 25
  2. ^ a b Jacobs, Bill. Acoustic Telephones, TelefoonMuseum.com website. Retrieved January 15, 2013. This article in turn cites:
    • Kolger, Jon. "Mechanical or String Telephones", ATCA Newsletter, June 1986; and
    • "Lancaster, Pennsylvania Agricultural Almanac for the Year 1879: How to Construct a Farmer's Telephone", John Bater's Sons.; and
    • "Telephone Experiences of Harry J. Curl as told by him to E. T. Mahood, During the summer of 1933 at Kansas City, Missouri: First Telephone Experience."
  3. ^ Grigonis, Richard. A Telephone in 1665?, TMCNet Technews website, December 29, 2008.
  4. ^ Giles, Arthur (editor). County Directory of Scotland (for 1901-1904): Twelfth Issue: Telephone (Scottish Post Office Directories), Edinburgh: R. Grant & Son, 1902, p. 28.
  5. ^ "Voicepipes and Speaking-Tubes". The Museum of Retro-Technology. March 15, 2010. Retrieved October 17, 2012. 
  6. ^ Jones, R. Victor Samuel Thomas von Sömmering's "Space Multiplexed" Electrochemical Telegraph (1808-10), Harvard University website. Attributed to "Semaphore to Satellite" , International Telecommunication Union, Geneva 1965. Retrieved 2009-05-01
  7. ^ Lewis Coe (1995), "The Telephone and Its Several Inventors"
  8. ^ "H.Res.269 - Expressing the sense of the House of Representatives to honor the life and achievements of 19th Century Italian-American inventor Antonio Meucci, and his work in the invention of the telephone. 107th Congress (2001-2002)". U.S. House of Representatives. Retrieved 7 February 2014. 
  9. ^ Private Telegraphs, The Sydney Morning Herald, credited to The Times, April 19, 1878, p. 6.
  10. ^ Puskás Tivadar (1844 - 1893) (short biography), Hungarian History website. Retrieved from Archive.org, February 2013.
  11. ^ "Puskás Tivadar (1844 - 1893)". Mszh.hu. Retrieved 2012-07-01. 
  12. ^ "Puskás, Tivadar". Omikk.bme.hu. Retrieved 2012-07-01. 
  13. ^ "Welcome hunreal.com - BlueHost.com". Hunreal.com. Archived from the original on 2012-03-16. Retrieved 2012-07-01. 
  14. ^ a b c d e f g Withdrawal of National Historic Landmark Designation: Site of the First Telephone Exchange, New Haven, New Haven County, Connecticut[dead link], United States National Park Service, United States Department of the Interior, April 13, 2006.
  15. ^ Francis S. Wagner: Hungarian Contributions to World Civilization - Page 68
  16. ^ "History Of The Invention Of Telephone". The Reverse Phone. 9 June 2011. Retrieved 22 April 2012. 
  17. ^ "Antonio Meucci - Questions and Answers". Chezbasilio.org. Retrieved 2012-08-30. 
  18. ^ Bennett, Alfred Roslin (1895). Telephone Systems of the Continent of Europe. p. 337. Retrieved 14 June 2012. 
  19. ^ "Early U.S. Telephone Industry Data". Retrieved 15 June 2012. 
  20. ^ "AT&T: History: Origins". Corp.att.com. Retrieved 2012-08-30. 
  21. ^ "Leaders in the early spread of telephone service". Purplemotes.net. March 21, 2010. 
  22. ^ http://www.porticus.org/bell/images/we-102.jpg
  23. ^ "1947 memo by Douglas H. Ring proposing hexagonal cells" (PDF). Retrieved 2012-08-30. 
  24. ^ Farley, Tom; van der Hoek, Mark (1 January 2006). "Cellular Telephone Basics". PrivateLine. Retrieved 22 April 2012. 
  25. ^ interview of Joel S. Engel[dead link], page 17 (image 18)
  26. ^ Kramarae, edited by Cheris; Lana F. Rakow (1988). Technology and women's voices : keeping in touch (1. publ. ed.). New York: Routledge & Kegan Paul. p. 209. ISBN 0710206798. Retrieved 9 February 2014. 
  27. ^ Kramarae, edited by Cheris; Lana F. Rakow (1988). Technology and women's voices : keeping in touch (1. publ. ed.). New York: Routledge & Kegan Paul. p. 217. ISBN 978-0710206794. 

Further reading[edit]

External links[edit]