Originally Posted by
hirch_duckfinder
As I understand it sillage is a product of volatility. Longevity (persistence) is determined more by the density, though the two are related.
Lighter, more volatile molecules will indeed fly off your arm faster and farther which is why they don't last as long on your skin. Heavier molecules will depart the mixture at a slower rate and travel a shorter distance, hence can smelled more near to the site of application. However, they may also hang around in the air in a denser concentration than the more volatile ones once they have left your skin. Sillage translates as "wake" as in the wake of a ship, or a trail.
Most fragrances would have lots of sillage for a very brief period of the top notes, then less but still enough (hopefully, if you want it) as the heart notes warm up from your body heat and develop. the heavier heart notes take longer to warm up with the energy of your body heat. Base notes usually have relatively very low volatility - and this is their function- to hold and slow down the dispersal of the top and heart (while adding to the fragrance of course) so that it lasts longer.