As part of my thesis, I have a short excerpt on EEG instrumentation history. I cited, for example, Hans Berger's original work using his own paper. However, Pat had a really good point, what I should cite is not Berger's paper but a paper or book which says that Hans Berger first reported human EEG in 1929. This has led me on a search for a definitive historical account of what happened. It appears to be Mary Brazier's "A history of the electrical activity of the brain; the first half-century" .
Fortunately, the book can be found in Lane Medical Library (lookup "Brazier history"). Unfortunately, it is checked out till the end of the year.
Mary Brazier (1961) has described the work of the German psychiatrist Hans Berger as the triumph of a man working with equipment that was inadequate even by the standards of his day. Like Caton, Berger attempted to record electrical responses to sensory stimuli in animals, although it seems that the work he did between 1902 and 1910 was in general unsuccessful. In 1924 he turned to the measurement of human electrical potentials but delayed publication of his results until 1929, when the first recorded electroencephalogram (of his young son) appeared in Archiv forschung Psychiatrie.Another useful source of information is the section entitled "Electrophysiological Recordings" in Stanley Finger's "Origin of Neuroscience: A History of Explorations into Brain Function" . Some useful excerpts appear below:
Berger discovered alpha rhythm, running at 10 cycles per second (hertz or Hz). He found that this disappeared if the eyes were opened, with mental effort such as doing mental arithmetic (with the eyes closed) and with loud noises or painful stimuli. Berger's work was disregarded by physiologists partly ecause it was published in psychiatric journals, and perhaps because of his reputation for eccentricity, seclusiveness and his outstanding belief in psychic phenomena such as telepathy. Only after his work was replicated by Adrian and Matthews in Cambridge did he get the credit he deserved for laying the foundations of human electroencephalography. Brazier's (1961) history of the EEG cannot be recommended too highly for readers interested in a full and authoritative account of the early days. 
Richard Caton (1842-1926) was probably the first to record the spontaneous electrical activity of the brain.I found some more useful comments on instrumentation in Hobson , e.g.,
Caton's first report was a presentation before the British Medical Association in Edinburgh in July 1875 and was summarized in the British Medical Journal later that year. Caton told his audience that the electrical changes taking place in the brain varied in location with the specific peripheral stumli he was using:In every brain hitherto examined, the galvanometer has indicated the existence of electric currents. The external surface of the grey matter is usually positive in relation to the surface of a section through it. Feeble currents of varying direction pass through the multiplier when the electrodes are placed on two points of the external surface of the skull. The electric currents of the grey matter appear to have a relation to its functions. When any part of the grey matter is in a state of functional activity, its electric current usually exhibits negative variation. For example, on the areas shown by Dr. Ferrier to be related to rotation of the head and to mastication, negative variation of the current was observed to occur whenever those two acts respectively were performed. Impressions through the senses were found to influence the currents of certain areas, e.g., the currents of that part of the rabbit's brain which Dr. Ferrier has shown to be related to movements of the eyelids, were found to be markedly influcenced by stimulation of the opposite retina by light. (1875, 278)Electrophysiological recordings became much more fashionable after Hans Berger (1873-1941) published his electroencephalograph (EEG) work on humans in 1929. Unlike almost everyone else, Berger cited Caton's valuable contribution to the field. In 1929, he wrote:Caton has already (1874) published experiments on the brains of dogs and apes in which bare unipolar electrodes were placed either on the cereral cortex and the other on the surface of the skull. The currents were measured by a sensitive galvanometer. There were found distinct variations in current, which increased during sleep and with the onset of death strengthened, and after death became weaker and then completely disappeared. Caton could show that strong current variations resulted in brain from light shone into the eyes, and he speaks already of the conjecture that under the circumstances these cortical currents could be applied to localization within the cortex of the brain. (Translated by Cohen, 1959, 258) 
Hans Berger used Einthoven's string galvanometer to record the electrical activity of the brain in human subjects .and
The rest of the world began to fall in line after 1933 when two English physiologists, Edgar Adrian and Brain Matthews, were able to confirm Berger's observation by recording their own brainwaves using their cathode-ray oscilloscope. This instrument substituted an electron beam for the lightweight string in Einthoven's galvanomter. Adrian and Matthews took advantage of the virtually weightless state of electrons. When a beam of electrons was moved back and forth across a phosphorescent screen, the external voltages were visualized as deviations of the beam's path. These distinguished English investigators gained for Berger's discovery the scientific support it needed. Ok, that last reference was a bit casual... but the comments about the cathode-ray oscilloscope are useful. I suspect that all this comes from Brazier's text, but confirming that will have to wait. Searching for more information on the string gavanomter I discovered Robert Bud's "Instruments of Science: An Historical Encyclopedia" . It gives a short but insightful treatment on EEG instrumentation.
The EEG evolved from research among physiologists in the 1800s on the electrical properties of animals. In 1875, Richard Caton of Liverpool, England, published reports on his detection of electrical activity in animal brains. Fifteen years later, a Polish physiologists, Adolf Beck, detected regular electrical patterns in the cerebral cortexes of dogs and rabbits.Note that the last statement is not quite right - since EEG is used in a lot of other fields. It was the authors conclusion to the use of EEG to decide on clinical death. The important quote I wanted was that EEG has changed little.
The successful introduction of Einthoven's electrocardiograph (EKG) in 1902 for disease diagnosis inspired further research on the brain. Investigators working on the brain quickly adopted the highly sensitive Einthoven string galvanometer. In 1914 Napoleon Cybulski and S. Jelenska-Macieszyna at the University of Crakow published their tracings taken with an Einthoven galvanometer from a dog during an epileptic seizure. The development of the triode amplifier for small voltages in radio signaling during World War I made it even easier to record the very small electrical signals in the brain.
The EEG has changed little since its first human applications in 1920s, but its function has reversed completely, from providing a characteristic tracing of life to demonstrating its absence. 
 M.A.B. Brazier, A history of the electrical activity of the brain; the first half-century, New York: Macmillan, 1961.
 J. Empson and M.B. Wang, Sleep and dreaming, Houndmills, Basingstoke, Hampshire ; New York, N.Y.: Palgrave, 2002.
 S. Finger, Origins of neuroscience : a history of explorations into brain function, New York: Oxford University Press, 1994, pp. 41-42.
 J.A. Hobson, The dreaming brain, New York: Basic Books, 1988, pp. 115-116.
 R. Bud and D.J. Warner, Instruments of science : an historical encyclopedia, New York: Science Museum, London, and National Museum of American History, Smithsonian Institution, in association with Garland Pub., 1998, pp. 207-208.