الموضوع: هل تولد الحياة من رحم الموت؟؟؟ دراسة بحثية
عرض مشاركة واحدة
قديم 11-08-2013, 11:55 PM
المشاركة 1643
الصورة الرمزية ايوب صابر
ايوب صابر
مراقب عام سابقا

اوسمتي

  • غير موجود
افتراضي
50-المسجل فلاديمير بولسون دنماركي

- مجهول الطفولة
- كان طالبا سيئا
- كان يكره الرياضيات ويحب الرسم والفيزياء
- رفض طلب والده دراسة الطب وعمل في ورش للماكنات
- ترك دراسة الطب وعمل في شركة الهواتف وهو في سن 24


Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer who developed a magnetic wire recorder in 1899.

He was born on 23 November 1869 in Copenhagen.
The magnetic recording was demonstrated in principle as early as 1898 by Valdemar Poulsen in his telegraphone. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A playback head (which may be the same as the recording head) can then pick up the changes in the magnetic field from the tape and convert them into an electrical signal.


Poulsen's US patent for a magnetic wire recorder.
Poulsen obtained a Telegraphone Patent in 1898, and with his assistant, Peder O. Pedersen, later developed other magnetic recorders that recorded on steel wire, tape, or disks. None of these devices had electronic amplification, but the recorded signal was easily strong enough to be heard through a headset or even transmitted on telephone wires. At the 1900 World's Fair in Paris, Poulsen had the chance to record the voice of Emperor Franz Josef of Austria which is believed to be the oldest surviving magnetic audio recording today.[1]
Poulsen developed an arc converter in 1908, referred to as the "Poulsen Arc Transmitter", which was widely used in radio before the advent of vacuum tube technology.
He died on 23 July 1942.
Legacy[edit]

---
Valdemar Poulsen, son of a Danish High Court judge was born 23rd November 1869 in Copenhagen. Valdemar was not a good scholar; the only subjects he was interested in were physics and drawing. He had no interest in mathematics, a trait he shared with many other great inventors. His father wanted him to become a doctor but after an unsuccessful time at medical school at the University of Copenhagen, 1889-93, at the age of 24, he obtained a position in the technical section of the Copenhagen Telephone Company. His work was mainly troubleshooting which allowed him a fair amount of time for experimenting.
*

While working there, Poulsen became interested in magnetic recording of sound. There seems to be no record of what gave Poulsen the idea of magnetising steel wire to make sound recordings. Maybe he had read an article written in 1888 by American scientist Oberlin Smith for the magazine Electrical World. In his article Smith discussed the possibility of permanent magnetic impressions for recording sound and suggested, as a medium, cotton or silk thread, in which steel dust was suspended. Smith also considered steel wire but didn't think it would be possible 'that it would divide itself up properly into a number of short magnets" to establish a magnetic pattern as a replica of currents produced by a microphone. Smith never built a machine or proved his theory practically.
Valdemar Poulsen, 1900

*

In an early experiment Poulsen stretched a steel wire between two parallel walls, inclined at such an angle that a small electromagnet suitably attached to the wire could, assisted by gravity, slide down the wire at a uniform speed. Wires attached to the electromagnet energised it from the voltage of a battery modulated by a microphone. For replay the battery was disconnected, and the microphone replaced by a telephone earpiece, the electromagnet returned to the top and let go. The experiment worked and Poulsen set about putting magnetic recording to use in the shape of a telephone answering machine.
Valdemar Poulsen, ca. 1898

*

On 1st December 1898, he filed a patent in Denmark for the Telegraphone (or in Danish, Telegrafoon), the first device in history to use magnetic sound recording. An extract from this patent reads: "The invention based upon the fact that when a body made of magnetisable material is touched at different points and at different times by an electromagnet included in a telephonic or telegraphic circuit, its parts are subject to such varied magnetic influences that conversely by the action of the magnetisable body upon the electromagnet the same sounds or signals are subsequently given out in the telephone or recording instrument as those which previously caused the magnetic action upon the magnetisable body."