vâyu-atom. The light-and-heat potentials combine with touch-potentials and sound-potentials to produce the tejas-atom. The taste-potentials combine with light-and-heat potentials, touch-potentials and sound-potentials to generate the ap-atom and the smell-potentials combine with the preceding potentials to generate the earth-atom. The âkâs'a-atom possesses penetrability, the vâyu-atom impact or mechanical pressure, the tejas-atom radiant heat and light, the ap-atom viscous attraction and the earth-atom cohesive attraction. The âkâsa we have seen forms the transition link from the bhûtâdi to the tanmâtra and from the tanmâtra to the atomic production; it therefore deserves a special notice at this stage. Sâ@mkhya distinguishes between a kâra@na-âkâs'a and kâryâkâs'a. The kâra@na-âkâs'a (non-atomic and all-pervasive) is the formless tamas--the mass in prak@rti or bhûtâdi; it is indeed all-pervasive, and is not a mere negation, a mere unoccupiedness (_âvara@nâbhâva_) or vacuum [Footnote ref 1]. When energy is first associated with this tamas element it gives rise to the sound-potential; the atomic âkâs'a is the result of the integration of the original mass-units from bhûtâdi with this sound-potential (_s'abda tanmâtra_). Such an âkâs'a-atom is called the kâryâkâs'a; it is formed everywhere and held up in the original kâra@na âkâs'a as the medium for the development of vâyu atoms. Being atomic it occupies limited space. The aha@mkâra and the five tanmâtras are technically called _avis'e@sa_ or indeterminate, for further determinations or differentiations of them for the formation of newer categories of existence are possible. The eleven senses and the five atoms are called _vis'e@sa,_ i.e. determinate, for they cannot further be so determined as to form a new category of existence. It is thus that the course of evolution which started in the prak@rti reaches its furthest limit in the production of the senses on the one side and the atoms on the other. Changes no doubt take place in bodies having atomic constitution, but these changes are changes of quality due to spatial changes in the position of the atoms or to the introduction of new atoms and their re-arrangement. But these are not such that a newer category of existence could be formed by them which was substantially different from the combined atoms. ___________________________________________________________________ [Footnote 1: Dr B.N. Seal in describing this âkâs'a says "Âkâs'a corresponds in some respects to the ether of the physicists and in others to what may be called proto-atom (protyle)." Ray's _History of Hindu Chemistry_, p. 88.] 254 The changes that take place in the atomic constitution of things certainly deserve to be noticed. But before we go on to this, it will be better to enquire about the principle of causation according to which the Sâ@mkhya-Yoga evolution should be comprehended or interpreted. Principle of Causation and Conservation of Energy [Footnote ref 1].