Name given to a model for the structure of the atom proposed by Sir Joseph John Thompson in the late 19th century in which atoms were invisaged as a spherical mass of positive charge with specs of negative charge - that is electrons. As such the electrons were considered to be like raisins embedded in the "pudding" that consisted of the rest of the atom. This model was soon shown to be innaccurate and improved upon by Ernest Rutherford although Thompson's discovery is still notable for being the first to establish that an atom is not, as by definition, indivisible but has separable sub-atomic structure.