Moses Pendleton's whimsical troupe, a hybrid of modern dance, circus and visual spectacle, celebrates its 35th anniversary with a nearly monthlong run of the new work "Alchemia." Like the fusion of science and magic that the title alludes to, Momix mixes physical dexterity, cunning illusions and versatile props and costumes in an 85-minute tribute to the elements: earth, air, fire and water.