Micah --
> How did we know to come up with a device to detect things > we're not aware of? That's an excellent question, Micah, and I suspect that you're raising it to support what seems to be your "subjectivist" view of reality. Craig has provided a good reference to the types of phenomena detectors and measuring instruments are used for and how they work. But this tells only part of the story, since what you're asking is: How do we know such phenomena exist? Let me try to answer this from the objectivist viewpoint. It is true that most electromagnetic radiation is undetectable to humans, except of course for the narrow band of relatively large waves that are visible to the eye as light, and a wider band of shorter wavelengths that are felt as heat. In fact, it is the effects of electromagnetic energy that led scientists to devise the various means of monitoring it. For example, you remember the Curies who used pitchblend to generate Röntgen radiation (x-rays) and won Madame Curie the Nobel prize for experiments that led to the development of medical radiography. Pitchblend is the ore from which uranium is extracted, yet was more radioactive than the uranium. By 1898 they deduced that the pitchblend contained traces of an unknown radioactive substance far more radioactive than uranium. Curie named this substance radium, and her death from aplastic anemia in 1934 was almost certainly the effect of her exposure to this substance. Since monitoring radiation exposure was critical, subsequent research led to the invention of scintillation counters which "convert" x-ray photons to visible photons and the Geiger Counter which measures the ionization rate of gases exposed to radiation. Since the 1970s, new semiconductor detectors have been developed that convert x-ray photons to electron-hole pairs in the semiconductor which are then collected to detect the X-rays. Practical application in Medical Imaging didn't occur until the 1990's. Amorphous selenium is now used in commercial large area flat panel x-ray detectors for chest radiography and mammography. Another observed effect of radiation that was applied to a whole new technology is electro-fluorescence. In the early 1900s it was discovered that cathode rays (a stream of electrons produced by a negative electrode) cause phosphors on the glass wall of a vacuum tube to fluoresce, an effect which eventually made possible the CRT now used to display television images. Similar histories can be cited for spectroscopy, the oscilloscope, x-ray astronomy, x-ray microscopy, and laser technology. In all of these developments, it was the observed "effect" of an unknown source of energy that initially led to a suitable detecting device (to identify the source), and eventually to an invention that could put it to practical use. The same could be said for the invention of the barometer to measure air pressure, the thermometer (temperature), photometer, (light), spectrograph (color), audiometer (sound), voltmeter (EMF), ammeter (electric current), etc. I think one could safely say that all "detecting" instruments are designed to measure and/or identify a phenomenon whose effects we are sensibly aware of. Now that I've explained the objective view, perhaps you'll tell us how the "subjective" view is different. Essentially yours, Ham, moq_discuss mailing list Listinfo, Unsubscribing etc. http://lists.moqtalk.org/listinfo.cgi/moq_discuss-moqtalk.org Archives: http://lists.moqtalk.org/pipermail/moq_discuss-moqtalk.org/ http://moq.org.uk/pipermail/moq_discuss_archive/
