Why is it that despite inventors' numerous enthusiastic marketing attempts, "Smell-O-Vision" remains a footnote curiosity? Could it be the olfactory sense is simply too intimate an intrusion for audiences to comfortably enjoy? No one has yet created a truly practical, easy-to-use (and thoroughly convincing) prototype, but the idea of a machine that can "play" scents the way a loudspeaker plays music has fascinated people for years. Ray Bradbury referred to "odorophonics" in "The Veldt," a short story from his 1951 book The Illustrated Man:

Now the hidden odorophonics were beginning to blow a wind of odor at the two people in the middle of the baked veldtland. The hot straw smell of lion grass, the cool green smell of the hidden water hole, the great rusty smell of animals, the smell of dust like a red paprika in the hot air...

The concept of odor-players has fascinated other futurists as well; Dune author Frank Herbert described an "odalarm" device in The Dosadi Experiment. Today's inventors are still trying to create a workable aroma player: Japanese firm K Opticom last July announced an Internet-based aroma delivery device called Kaori Web.

Trial units of the "Kaori Web" system will be placed at K Opticom's internet cafes in Japan until the end of September. But what is the "Kaori Web," you ask? See a picture of a flower, smell a flower. See a picture of waffles, smell waffles. The "Kaori Web" helps some realize their dream of having computers produce scents, to immerse them into a new environment finally covering all five senses. Or hackers will just use it to make some websites smell like a dog exploded.

Another company, Trisenx, has a series of sophisticated computerized odor-players, like the $369 Scent Dome™ which releases controlled blends of dozens of primary fragrances to generate a palette of virtual aromas - Technovelgy.com describes the Scent Dome™ as a kind of "printer for smells". It's an apt analogy, since unlike audio speakers and television screens that use transducers to convert electricity to sound or light, a smell-player, like a printer, would require reloadable cartidges of dispersable scents.

However, the main technical difficulty in creating a real odor-player comes from the fact that smell is likely the least-understood sensory modality. Various theories have tried to explain the mechanics of how the brain perceives and categorizes aromas. One of these, the "primary smells" concept, believes there are a small number of basic aromas that combine like primary colors to create the fragrance spectrum. Some recent research suggests that like sight and hearing, the vibrational frequency of molecules we sniff may be an important clue in unlocking the mysteries of smell.

The remote-identification value of one's personal aromas hasn't been lost on our government, either, as DARPA [Defense Advanced Research Projects Agency] claims to be developing a device that can identify individuals by their scents:

Researchers have shown that mice release a urinary odor that is genetically unique, DARPA says. It's based on the combination of acids found in varying concentrations. So if it's possible to detect an individual mouse, why not a human by the smell of his or her urine or sweat?

If scientists can prove that it works within two and a half years, DARPA wants to build a prototype within six years, spokeswoman Jan Walker said. Such a detector would essentially allow on-the-fly DNA identification, measuring and collecting yet another biometric, or identifying characteristic of the human body, Walker said.

Steven Aftergood of the Federation of American Scientists, a Washington group that circulated news of DARPA's proposal, warns that such a detector ? if it were ever built ? might be confused by myriad and changing odors that people exude.

Maybe Smell-o-Vision hasn't caught on because unlike sight and hearing, which rely on relatively "impersonal" electromagnetic radiation or air pressure waves impinging on the body's sense receptors, smell and taste require actual mucous membrane contact with molecules of the substance to be detected. Try not to think of that next time you're in a crowded public restroom.

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