Abstract: The mechanism of the present invention provides jet sprays of mixed water and air which continuously sweep up and down the spine of the user as he/she sits in the spa. The jets undergo a partial rotation about pivots in arcs of about 1/4 or 1/3 of a circle and then reverse and return. These arcs of spray direct the spray directly against the user's back in their midpoint of rotation and obliquely at the end points. Thus, the pressure of spray as felt by the user is continuously changing. This motion is accomplished by an impeller and worm gear arrangement which converts the energy of the water which is flowing to the jets.