The Silph scope is a scope created by Silph Co., and is said that you can see ghosts when wearing it.
It is obtained when you beat Giovanni, the leader of Team Rocket, the first time in Rocket Hideout, which is in Celadon City in Kanto.
It is used in Lavender Town, to gain access to the top of Lavender Tower so that you can get the Poke Flute, removing the Snorlax from Route 12.