Milestone-Proposal:Sonar, 100th birthday of Paul Langevin Invention 1917-2017

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Docket #:2014-04

This Proposal has been approved, and is now a Milestone

To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:

1915-1918

Title of the proposed milestone:

Invention of Sonar, 1915-1918

Plaque citation summarizing the achievement and its significance; if personal name(s) are included, such name(s) must follow the achievement itself in the citation wording: Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons.

From 1915 to 1918, Paul Langevin demonstrated the feasibility of using piezoelectric quartz crystals to both transmit and receive pulses of ultrasound and thereby detect submerged submarines at ranges up to 1300 metres. The system, later called sonar, validated Constantin Chilowsky's proposal to use ultrasound for this purpose. The technology was used successfully during World War II, and led to other applications including depth sounding and medical echography.

Justification for inclusion of Prof. Paul Langevin’s name in the Milestone Plaque Citation:

The invention strongly relies on the careful design and the experimental skills of Paul Langevin who invested his time and energy in solving the problem. It is to be noted that it was not part of a regular Laboratory work but was only performed upon his own initiative. It is his privileged knowledge of electromagnetism, electricity, wave propagation and piezoelectricity that enabled this invention.

See for instance [2] : p 43-44

Chilowsky’s proposal:

Constantin Chilowsky had originally submitted a patent indicating the « possibility of producing the desired elastic high frequency waves by transforming the electric oscillations of high frequency commonly used in wireless telegraphy. » However Paul Langevin who was made aware of this application immediately realized that the use of magnetic fields was highly problematic. He writes [2]: « To effect this result, M. Chilowsky proposed to utilize the medium of magnetic attraction produced by the current, acting synchronously on all points of the internal face of a plate of soft iron, finely laminated, in contact with the water at its external face, and of a proper size in relation to the wave-length of the elastic vibrations in the water, so as to produce an emission almost entirely confined to a central cone of diffraction, in accordance with the phenomena of the distant diffraction of plane waves through an opening of the same shape as the plate employed. No method of receiving, however, was indicated. »

Paul Langevin will have to reconsider the device and will consider a vibrating capacitor in order to have the necessary power to provide sufficient sensitivity. In his presentation, partially transcripted below, at the Interallied Conference on the search for submarines by the ultrasonic method: History of research carried out in France (19 October1918), Paul Langevin writes : « When this proposition came before me, l was struck by the insurmountable difficulties involved in the magnetic field, and thought that the chances of success, although still small, would be increased by having recourse, in effecting the transformation to the electrostatic attraction between the armatures of a plain condenser, periodically charged by the high-frequency current. The internal armature of this condenser being insulated, and the other armature in contact with the water by its exterior face, the periodic attraction between them is transmitted to the water, giving rise to the emission of elastic waves of a frequency double of the electric frequency and with the maximum of radiation, obtained either by making the external armature sufficiently thin, or by giving it a thickness equal to half the wavelength of the longitudinal elastic vibrations in the metal used. » « I proposed, in March 1915, to the Navy Department that this research work be undertaken, and that it be initiated in my Laboratory at the School of Physics and Chemistry… When the development of the work justified it, the military authorities consented to place at my disposition as collaborators, the services of M. Marcel Tournier, Director of Practical Work at the School of Physics and Chemistry, and of M. Fernand Holweck of the Sorbonne; the former since September 1915, the latter since July 1917. I [Paul Langevin] applied with M. Chilowsky for a patent on the principle of the method, and on the apparatus actually constructed. »

This first patent was filed in May 1916. Procédés et appareils pour la production de signaux sous-marins dirigés et pour la localisation à distance d'obstacles sous-marins, Constantin Chilowsky et Paul Langevin. [P1]

The divergences between Langevin and Chilowsky:

In spring 1916, as a result of disagreements with Langevin, Chilowsky left the research, leaving the French physicist in full charge. (See [1])

In [3], one can find the following text: « Chilowsky’s proposal was forwarded by the under-secretary of state for inventions to Professor Paul Langevin, an early supporter of the theory of relativity and an expert on paramagnetism, diamagnetism, secondary X-rays and the behaviour of ions. Langevin concluded that Chilowsky’s basic idea had merit, but that his means to produce a suitable sound wave was unlikely to succeed. Langevin decided to begin research into developing a practical means to create an intense pulse of high-frequency sound. He asked Chilowsky to join him and a small team of scientists working at his laboratory at the School of Physics and Chemistry in Paris. By April 1916 results were so promising that the French Navy transferred their work to Toulon so that experiments could be undertaken at sea. At about this time, Chilowsky parted ways with Langevin and left to pursue other military research. Although it is reported that Chilowsky’s departure was not cordial, in the years ahead Langevin was careful to give the inventor equal credit for the discovery of sonar. Despite having taken no active part in the post-war legal proceedings, Langevin insisted Chilowsky be treated as an equal partner in the claim for compensation. »

The invention of the SONAR: Paul Langevin and the Quartz transmitter and receiver: If the use of ultrasound was the fundamental principle, the realization through the use of the piezoelectric effect was the real paradigm shift. It enabled both emission and detection.

« In spite of these encouraging results, it was still very difficult to use the apparatus. Beside the disruptive accidents already mentioned in the mica condensers, which l was trying at that time to avoid by substituting heterodyne lamps for the arcs used in the sending apparatus, the microphone gave very irregular results, and required delicate regulations in order to keep the sensibility of the carbon contacts approximately constant against the variations in outside pressure due to the movement of the sea. In order to avoid these difficulties, l thought (February 1917) of utilizing the piezoelectric properties of quartz, first of all for receiving… This success in the use of quartz as a receiver led me to try (April, 1917) if it would not be possible to utilize it as well for sending supersonic waves, thanks to the inverse phenomenon of piezoelectricity »[2]

The SONARs that were then used during WWII and later on, untill nowadays are indeed based on the use of the piezoelectric effect, whose idea, design and practical realization were entirely due to Paul Langevin (with technical and experimental help from M. Tournier and F. Holweck), according to the second patent filed in 1918, under his sole name.

Patent applied in September 1918: Procédé et appareils d'émission et de réception des ondesélastiques sous-marines à l'aide des propriétés piézo-électriques du quartz. Paul Langevin. [P3]

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

In what IEEE section(s) does it reside?

France

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE France
Senior Officer Name: Claire Lajoie-Mazenc

Unit: ESPCI Alumni
Senior Officer Name: Sylvain Gilat

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE France
Senior Officer Name: Claire Lajoie-Mazenc

IEEE section(s) monitoring the plaque(s):

IEEE Section: France
IEEE Section Chair name: Claire Lajoie-Mazenc

Milestone proposer(s):

Proposer name: Brigitte Leridon
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

ESPCI Paris - 10 rue Vauquelin -75005 Paris France

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. Historic site. Paul Langevin was Professor at ESPCI . Sonar has been invented in ESPCI (Ecole Superieure de Physique Chimie Industrielles) in Paris (http://www.espci.fr/en/)

Are the original buildings extant?

Yes; both the Laboratory and the office of Paul Langevin still exist.

Details of the plaque mounting:

On the wall outside of Langevin's laboratory, next to the building where he had his office.

How is the site protected/secured, and in what ways is it accessible to the public?

The plaque site will be on Rue Vauquelin, out of reach of pedestrians but visible by all public. It will be on the outside wall of the laboratory where Paul Langevin worked on the sonar in a sink that is still visible inside the Lab.

Who is the present owner of the site(s)?

ESPCI (http://www.espci.fr/en/)

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include detailed support at the end of this section preceded by "Justification for Inclusion of Name(s)". (see section 6 of Milestone Guidelines)

Historical context:

 In 1912 the Titanic sank after colliding an iceberg. A few months later, an English scientist Lewis Richardson filed a patent for echolocation of icebergs in water. The detection of undermarine objects was also investigated by Alexander Belm in Austria and Reginald Fressenden in the US.

The First World War had created a maritime blockade around Great Britain, that was the allies base for logistics. Aware of this situation, the German Minister von Brettreich declared: "Our submarines will have completed their glorious task in a few months and we will have won the war". The considerable extent of the maritime losses inflicted on the Allies by the German submarines made therefore necessary all scientific and technological efforts to detect them.

The birth of modern ultrasonics: The period beginning around 1916 can be considered as the start of modern ultrasonic development. Indeed , the idea of using high-frequency elastic waves to detect obstacles through echo technique was first proposed by M.L. Fry Richardson in 1912, in an English patent. In 1915, Constantin Chilowski submitted to the French government a project using submarine ultrasound waves to detect submarines and mines. The aim was to use a vibrating antenna of such dimensions that it could, on reception, provide sufficient directional localisation to have usable telemetry. The French Ministry of the Navy commissioned Paul Langevin to examine this proposal. The latter gave up his previous research interests to fully investigate the use of piezoelectric transducers in order to design an ultrasonic detection device able to detect both distance and direction. Two different technologies were then studied: the vibrating capacitor (1916 Chilowski-Langevin patent) and the quartz capacitor (1918 Langevin patent). The latter proved to be the most promising. At this time, E. Rutherford in UK was also working on devices using ultrasound, as well as R.W. Boyle in Canada, who built a quartz ultrasound transducer in 1917. Exchanges of information concerning French work on ultrasonics began in 1917, during which M. Langevin visited England twice. At the end of May 1917, after the successful tests of quartz both in reception and emission, Sir Ernest Rutherford and Commander Bridge came to Paris where M. Langevin informed them of the latest results. Sir Ernest Rutherford and the British officer then joined Professors Abraham and Fabry on a scientific information mission to the USA. In August 1917, the American physicist Wood visited Langevin to show him the effects of high intensity ultrasound on fish. Dr R.W. Boyle of the Admiralty Experimental Station of Harwich came to Toulon in July 1917 and returned in June 1918 at the time when the US equipment with steel quartz triplet and triodes was ready for a first practical implementation. After two convincing official tests in front of the Commission d'Etudes Pratiques des Armes sous-marines in June and July 1918, the results of which are recorded in a report by M. de Broglie on July 10th 1918, the French Navy manufactured 6 ultrasonic devices for submarines search. These will only be ready after the armistice. In October 1918 an inter-allied conference on SONARs met under the presidency of M. Cels. See[4].

Impact of the invention: While these efforts had little effect during the first world war since they were mature only by the end of the conflict, they had a considerable impact during the Second World War. These developments also paved the way for civil applications such as, for instance the use of medical ultrasound to visualize the interior of a non-transparent environment in echography. Developments in this field are still very active, and still noticeably rely on the use of piezoelectric materials. The same technology also contributed to the early development of depth sounding, that was particularly important for the laying of underwater cables by telegraph companies and the establishment of marine charts by military hydrographic services, with an improved patented sounder developed by Langevin and Florisson from 1919 to 1924. See [5]. This work is also pioneering in its use of applied and basic science (and not just empirical approach) to solve military problems. It helped proving that scientific advance can result in military advantage.

The acronym SONAR means « Sound Navigation And Ranging », and was used for the first times during WW2. One can make a distinction between passive SONARs, such as microphonic devices and active SONARs, which emit a sound in the water to detect an echo from the obstacle and determine its direction and distance, of the type that was invented by Langevin and Chilowski. The word SONAR is also used for dolphins and some whales which use an active echolocation technique.

What obstacles (technical, political, geographic) needed to be overcome?

Original idea: In February 1915, Constantin Chilowski submitted to French Minister Paul Painlevé a first project to emit ultrasound using an electromagnetic vibrator powered by high frequency signals similar to those used in wireless telegraphy. The idea was to build on Reginald Fessenden's idea to use sonic echo method for location of icebergs by doing ultrasonic echo detection. Paul Langevin, immediately informed by the French Navy Ministry, decided to work with Chilowski on the device. He retained the idea of ultrasound but preferred to direct the research in another direction: to use electrostatic attraction between the fittings of a capacitor, instead of the magnetic emitter proposed by Chilowski. In June 1915, with the help of Marcel Tournier, a first experiment was carried out in the laboratory of the Ecole de Physique et Chimie de la Ville de Paris to evaluate the power radiated by a device excited at 100 kHz. A second device emitting at 40 kHz was designed to be immersed. An original solution was chosen: the mica sheet, originally inserted between the fittings of a capacitor, was in direct contact with conductive water. Acoustic range measurements were carried out in December 1915 over a distance of 100 m between the banks of the Seine, then over a distance of up to 2000 m off Toulon; a granular microphone was used as a receiver and a very clear echo was obtained for the first time at 100 m on a 2-square meter-shielding plate and then on a 90-cm-diameter mine. A patent was subsequently filed on May, 29th 1916 [P1,P2], acknowledging equal contributions from Chilowski and Langevin. In order to improve the detection of acoustic signals - the sensitivity of the granular microphones was found to vary with hydrostatic pressure, Paul Langevin then considered piezoelectricity.

Technical obstacles: The idea of using piezoelectricity was indeed briefly considered by Ernest Rutherford who was conducting similar research. Rutherford focussed mostly on passive methods for sonic detection of boats (sonic hydrophones). In september 1916 he considered using piezoelectricity for detection of sound waves, and also for emission of supersonic waves (without mention to echo detection). However, during the experimental attempts that he conducted, he simply made use (at finite frequency) of a specific quartz designed by Pierre Curie for his famous piezoelectric balance, that was aimed as a high-sensitivity detector (used by Marie Curie to measure radioactivity) and which exploited transverse piezoelectric effect. This choice prevented Boyle (to whom Rutherford had sent a quartz crystal coming from Paris) to obtain sufficient power for the suitable generation of ultrasounds in water. Langevin on the contrary, designed and cut a specific set of quartz, taking advantage of the longitudinal piezoelectric effect and aimed at producing ultrasound power generation. Is it probably because of the proximity that he had had with Pierre Curie, his mentor at Ecole De Physique et Chimie Industrielle, discoverer of the piezoelectricity effect with his brother Jacques, and theorist of the symmetry principles that describe the relation between cause and effect, that he was able to sufficiently master the piezoelectric effect, understand that the effect could lead to successful wave generation and detection and to conceive and build a suitable device. [1]

Achievements specifically due to Paul Langevin: Paul Langevin was able to invent a sonar device giving both distance and direction with sufficiently sensitivity using tow major ideas: - The detection of wave direction was only possible by using transducer with diameter larger than the wavelength, so about at least 20 cm, which was too large to consider monocrystalline quartz. Langevin had the idea of cutting several crystal quartz along the same cristallographic axes, polishing them to the same thickness and pasting them together side by side, thus creating a large diameter transducer. - Given the performances of the electronics available at the time, Langevin decided to work in resonant mode, in order to improve the sensitivity of the device. One possible option would have been to work with a thick quartz, but this would have been at the expense of the capacitance, thus creating high impedance adaptation issues. Langevin therefore had the idea to create a mechanically resonant structure with several relatively thin quartz separated by steel plates, giving birth to the famous Langevin triplet (or even in some cases Langevin quintuplet).

In February 1917, Paul Langevin used a quartz blade as a receiver for the first time. Four months later, the same quartz was used as a transmitter. The problem of emission-reception switching having been solved by Marcel Tournier of the laboratory of the Ecole de Physique et Chimie de la Ville de Paris, the detection of echoes of an ultrasonic wave was first carried out in February 1918; the reflector was constituted by the gate of the Vauban basin of the Toulon arsenal (France). On May 4th, 1918, the submarine Messidor was detected at 500 m.[P3] Impressed by this invention, the British government delegated the Canadian Richard William Boyle to Paul Langevin. The latter, in charge of coordinating research with the admiralty in this field, went to Toulon. Aware of the importance of underwater acoustics, the Allies met in Paris, just before the armistice, to create the Allied Submarine Detection Investigation Committee (ASDIC). This designation was very successful until the day it was replaced by SONAR (SOund-NAvigation-Ranging), an acronym to which one of the two adjectives "active" or "passive" was added. The latter describes the listening systems that were the only ones used during the conflict, the first being systems based on sound emission followed by detection of the echo returned by a target. See the photograph of a 1925 device File:SondeurLangFlo.pdf.

Performances (from “La Revue maritime n°208. 1964”): An active SONAR consists of three distinct parts: the transducer (vibrating capacitor/quartz triplet), the exciter pulse transmitter and the receiver for the echo coming from the reflection of the sound wave on the obstacle. Concerning the transducer with a vibrating capacitor in June 1915 the acoustic power produced was 0.33 W/cm2 for a voltage of 2500 to 3000 Volts RMS and a frequency of 100 kHz. In December 1915 tests were carried out on the Seine in Paris over a distance of 100 m and exchanges were transmitted from one point to another. In 1916 the tests continued in Toulon. Langevin and two of his collaborators, Marcel Tournier and then Fernand Holweck, increased the range to 500 m, then with a microphone receiver at the focus of a spherical mirror 35 cm in diameter, the range reached 2000 m. The transmitter is a 2.5 kW arc. In May 1916, after the development of an emission-reception switch, a very clear echo was obtained for the first time at 100 m on a 2 m2 shielding plate and then on a 90 cm diameter mine. At the beginning of 1917, the arc was replaced by lamps and 100 W of ultrasound was produced. The decisive turning point was the quartz triplet. In May-June 1917 the emission reached 10 W per cm2 at a voltage of 40,000 to 60,000 volts. In view of these very high voltages, the quartz device was replaced by a paving of quartz single crystals cut in a similar manner. In november 1917 with a 500 W transmitter a transmission range of 3000 m was obtained. On february 26th of 1918, with new triplet steel-quartz-steel and new device emission-reception, very good echoes were obtained at 800 m on a door of the basin Vauban of the arsenal of Toulon and on a ship with 100 W of radiated power. Actually, it was demonstrated that a system of piezoelectric quartz plates mounted to the two sides of a steel disc was able to project a beam of ultrasound waves that had a wave frequency of 150 kHz and a power output of 1 kW. As was noticed by Wood in 1917, when the ultrasound beam was insonated into a water tank, all the small fishes that tried to swim across the beam were immediately killed. Also, an instant painful burning sensation was felt when a person’s hand was held in the vicinity of the ultrasound beam. On May 4th echoes at 400 and 500 m were detected on the submarine Messidor. On May 15th transmissions at 8000 m, echoes at 600-800 m were recorded. The tests ended around July 1918. The official conclusion was: "The method of echo by ultrasound provides a new and efficient procedure which is now applicable for the pursuit and attack of submarines in diving as soon as the depths reach forty meters."

What features set this work apart from similar achievements?

The need to detect an obstacle, such as an iceberg in the case of the Titanic sinking in 1912, had boosted research in the field of radio waves. However in order to detect underwater obstacles, electromagnetic waves were no longer an option, and sound waves were considered. And in this context, Langevin and Chilowski built together the first active SONAR, that was shortly after improved thanks to Langevin’s detailed knowledge of piezoelectricity. In the first patents, the transmitter was a vibrating capacitor associated with a granular carbon microphone [P1, P2]. However the accurate detection of underwater obstacles required the optimization of the transmitter diameter and transmission frequency. This led Paul Langevin to take an interest in piezoelectric quartz and to use it as a receiver [P3]. Since the amplifier associated with quartz in echo reception has a high gain, it was necessary to find a way to avoid blinding it during emission and several "electronic" difficulties had to be solved. The problem of signal recording was solved later on. This achievement was the first realization of an ultrasonic echo detection (active SONAR). It was elaborated in a war context where its inventor, Paul Langevin gave up completely his current research to contribute to this invention. The novelty of this work was to use piezoelectric effect for emission and reception of ultrasounds with sufficient sensitivity and in a way that both distance and direction of the undermarine object could be inferred [P1,P2, P3]. Langevin and Chilowski’s SONAR represented a breakthrough compared to other techniques that were used for submarine detection at that time. Indeed, around 1917, the Royal Navy tried to train sea lions to track German U-boats. They were trained in pools by Joseph Woodward, a famous sea lion trainer at that time, but unfortunately they were not very focussed while in the open water. Once, while supposed to chase a Royal Navy Submarine, they opted for chasing fishes instead and went missing for hours!

Why was the achievement successful and impactful?

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

Langevin Patents :

[P1] Chilowsky CM, Langevin MP. Procédés et appareils pour la production de signaux sous-marins dirigés et pour la localisation à distance d’obstacles sous-marins. French patent #502913, 1916 File:Patents, 1916-17 Chilowsky and Langevin.pdf French version of the following patent.

[P2] Chilowsky CM, Langevin MP. Production of submarine signals and the location of submarine objects. US Patent #1471547, 1917 File:Patents, 1916-17 Chilowsky and Langevin.pdf

[P3] Langevin MP. 1918 ‘Procédé et appareils d’émission et de réception des ondes élastiques sous-marines à l’aide des propriétés piézo-électriques du quartz’ (Brevet francais, No. 505703, 17 Septembre 1918)File:Brevet 505.703 1918.pdf File:Translation Résumé French patent 1918.pdf

[P4]: Langevin, Paul, 'Piezoelectric signaling apparatus', US Patent 22498870, N° 390,542, June 21rst 1920 File:US2248870.pdf

References: [1] Shaul Katzir, Who knew piezoelectricity? Rutherford and Langevin on submarine detection and the invention of sonar, Notes and Records, The Royal Society Journal of The History of Science, March 7, 2012 File:Rsnr.2011.0049.pdf [2] David Zimmerman, Paul Langevin and the Discovery of Active Sonar or Asdic, The Northern Mariner/Le marin du nord, XII, No. 1, pp. 39-52, January 2002 File:Tnm 12 1 39-52.pdf [3] David Zimmerman, “‘A more creditable way’: The discovery of active sonar, the Langevin–Chilowsky patent dispute and the Royal Commission on Awards to Inventors. War in History 2018, Vol. 25(1) p 48–68 [4] Interallied Conference 1918 p13 and its partial translation. File:Text from Interallied conference 1918 P13.pdf [5] Benoit Lelong:"How to coordinate labs and open sea experiments ? Forms of innovation in the French and English navies", in Documents pour l'histoire des techniques (2011) File:Benoit Lelong's paper (translated).pdf

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.

File:Patents, 1916-17 Chilowsky and Langevin.pdf File:US2248870.pdf File:Brevet 505.703 1918.pdf File:Translation Résumé French patent 1918.pdf File:Rsnr.2011.0049.pdf File:Tnm 12 1 39-52.pdf File:Text from Interallied conference 1918 P13.pdf File:Benoit Lelong's paper (translated).pdf

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