Consider the following statements regarding cams :

1. A cam in which the follower moves radially from the centre of rotation of the cam is known as a disc cam.

2. A globoidal cam is a double-disc cam, the two discs being keyed together and are in constant touch with the two rollers of a follower.

3. A conjugate cam can have two types of surfaces, convex or concave.

4. In a spherical cam the follower oscillates about an axis perpendicular to the cam, the axis of rotation of the cam.

Which of the above statements are correct?