An electronic cigarette seems to be based on the old fashioned cigarette holders seen in old movies. The e cigarette comes equipped with a battery on one end and a cartridge holder on the other. The cartridge contains all the nicotine that you crave without the ash of a conventional cigarette.
Not only does the cartridge come in different nicotene strengths but they are, of course,replaceable. With an e cigarette, a smoker can get his dose of nicotene or of another non nicotene herb without violating the no smoking laws found in public places. There is also the added advantage of not having to worry about ashes as the cartridges are not conventional cigarettes but cigarette substitutes.
Another advantage of the e cigarette is in the health hazard that is claimed by advocates of banning cigarettes in public due to second hand smoke caused by the emitted carbon of burning tobacco. With an e cigarette there is no carbon emission as the electronic cartridge is pure nicotene or other product that burns safely without ash and without carbon emission which also, by the way, is healthier on the cigarette smokers lungs. The smoker gets to even try to wean himself off of nicotene with the cartridges available in different nicotene strengths while protecting his lungs from accumulating carbon from burning tobacco ash.