Wednesday, February 22, 2017

Hertz and his radio waves

‘Before lunch I went to an optician to find out the price of a battery and an electromagnet; but he said he did not stock the inferior sort and those he had were too expensive for me. Therefore I went to Prof. Boettger after luncheon to ask him whether I might be allowed to use the instruments of the Physical Society. He told me to write to the president, which I did that evening. I have not yet received an answer. Perhaps I shall not get one, or only a refusal; then I shall wait till I am home for Christmas.’ This is from the diaries of the German physicist, Heinrich Hertz, then only 18 years old, but demonstrating a precocious enthusiasm for his subject. Hertz, born 160 years ago today, was the first to demonstrate the existence of radio waves and that they could be broadcast and received, but he died tragically young in his mid-30s.
Hertz was born on 22 February 1857 in Hamburg, the oldest of five children of a weatlhy and prominent family. He showed an early aptitude for maths and science, and started to study civil engineering. However, after time in Frankfurt and then Dresden, he left to do military service in Berlin. Subsequently, he continued to study in Munich though concentrating more on a physics research career. In 1878, he returned to Berlin, to work under Gustav Kirchhoff and Hermann Helmholtz, where he received his doctorate in 1880. After, as Helmholtz’s assistant he focused on properties of mechanical hardness and stress, and produced a number of important research papers.

In 1883, Hertz moved to the University of Kiel as a lecturer, and directed his research more towards electromagnetism. In 1885, he accepted a full professorship at Karlsruhe’s Technische Hochschule. In the following year, he married Elizabeth, daughter of a colleague, and they had two daughters. By the end of the decade, Hertz’s research had overturned the existing paradigms for understanding electrical and magnetic phenomena: he demonstrated that electromagnetic effects take place in time, not instantaneously, and discovered the existence of radio waves, and that they behave like light. By doing so, he validated pre-existing theories put forward by the British scientist James Clerk Maxwell.

Hertz’s work on electromagnetic waves was first published in 1888 and elevated him to be counted among the leading physicists of the day. It also led to him moving, in 1889, to the University of Bonn where he continued research on the discharge of electricity in rarefied gases. His scientific papers were translated into English and published in three volumes, two of them posthumously - Electric Waves (1893), Miscellaneous Papers (1896) and Principles of Mechanics (1899). In 1892, he was diagnosed with an infection and underwent several operations, but he died in 1894 aged only 36. The unit of frequency - cycle per second –-was named the ‘hertz’ in his honour. Further information is available from Wikipedia, Engineering and Technology History, Magnet Academy, and MacTutor.

A first edition of Hertz’s memoirs, letters and diaries was arranged by his daughter Johanna Hertz and published in 1927. A second bilingual edition, revised and extended, was published in 1977 at the behest of Hertz’s youngest daughter, Dr. Mathilde Hertz - 
Heinrich Hertz: Memoirs, Letters, Diaries. This was translated by Dr Hertz herself, Lisa Brinner and Charles Susskind and published by Physik Verlag in the Federal Republic of Germany and by San Francisco Press in the US. A review can be read at the website of the University of Chicago Press Journals (Isis 70, no. 2 - June 1979). Although, as a younger man, Hertz wrote some longer entries in his diaries, later in life the entries were mostly very short and factual (see photo). Here are several extracts.

3 January 1867
‘I have a new satchel and a new pen case that I have already used at school, Mama hopes I shall bring home only good reports in the new satchel. I hope so too, but I do not believe it. Yet I will try hard.’

24 October 1875
‘The weather was so bad I could not go out. I read, mostly Wüllner’s Physics, and since I had previously known little about hydrostatics, I found it very interesting.’

8 November 1875
‘Before lunch I went to an optician to find out the price of a battery and an electromagnet; but he said he did not stock the inferior sort and those he had were too expensive for me. Therefore I went to Prof. Boettger after luncheon to ask him whether I might be allowed to use the instruments of the Physical Society. He told me to write to the president, which I did that evening. I have not yet received an answer. Perhaps I shall not get one, or only a refusal; then I shall wait till I am home for Christmas. There was a very interesting lecture by Prof. Boettger this evening. He talked about sulfur and phosphorus.’

11 December 1875
‘In the meantime the business with the Physics Club has been brought to conclusion, and I feel ashamed of my own rashness. For after receiving a letter on November 29, I went to the Senckenberg library and found Dingler’s Journal there; I leafed through it and soon found all sorts of articles about telegraphy, in fact I came to wonder whether my idea might not have been executed long ago. Therefore I did not go to Dr. Mappoldt right away, as I had intended, but decided first to return to the library on Tuesday. There I realized that it would be folly to set up experiments on something of which I knew as little as I did, and in the end I had to admit it was just as well that there had been some doubts about the propriety of my working in the laboratory, and I therefore withdrew my request. But from then on I went to the library almost every day, and I found a book listed there: Zetzsche, Development of Automatic Telegraphy. I ordered it and on receiving it yesterday I discovered that my idea was the fundamental concept of the entire field of automatic telegraphy; of course no part of it was executed as I had imagined, and the system that came closest to mine, that of Chauvassaigne et Lambrigot, was already obsolete. However, it seemed to me that even they did not formulate the idea that everybody could write his telegram at home on a paper strip supplied by the post office, which ought to have tremendous advantages. After leafing quickly through the periodicals in the reading room, I concentrated on The Development of the Chemical Industry from the Reports on the Vienna World Fair. At home I mostly read Tyndall, Heat as a Form of Motion. At the office I am occupied with copying the plans for the new stock exchange building in reproducing ink. Yesterday I had a new idea which I will perhaps test at home, at Christmastime; namely, to construct large-size lenses by introducing a liquid between two (if possible circular) glass plates of great elasticity and subjecting it to pressure, which will cause the glass plates to bulge out, and the central part of the bulge will probably come close to satisfying the conditions of a lens of large focal distance, at least close enough to collect a quantity of rays even if a clear image is not obtained. The question is only whether the glass is sufficiently elastic to withstand such deformation. To be sure, such a lens would lead to further difficulties in use.’

22 December 1875
‘This evening I am going to Hamburg for the holidays. Since my last entry I have had a very busy time at the office as the stock exchange roof neared completion, which entailed strenuous calculations, as did the new bridge across the Upper Main in the past few days. On the other hand, I did practically no work at home, because I did not want to start anything big before Christmas. Joyful anticipation of Christmas has been my main feeling. I have made so many plans of what to make on the lathe and in the laboratory while I am at home, that I fear very little of it will come to fruition. Yesterday and today were still full of interest. An unusually interesting lecture was held at the Physics Club, in which Prof. Boettger demonstrated a new piece of apparatus, in which a set of rotating vanes in vacuum is set in motion by light alone (radiometer).’

29 April 1885
‘Set the generator going and wanted to undertake some measurements with it, but the gas motor was not quite up to it.’

21 May 1885
‘Considered a current regulator for the generator.’

27 May 1885
‘Constructed a battery of 230 Planté cells and thought about electrodynamic experiments.’

22 December 1887
‘Experimented. Phase effect in the wire. Radical experiments on the velocity of propagation of the electrical effects.’

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