Gross matter, as the possibility of sensation, has been divided into five classes, according to their relative grossness, corresponding to the relative grossness of the senses. Some modern investigators have tried to understand the five bhūtas, viz. ākāśa, marut, tejas, ap and kshiti as ether, gaseous heat and light, liquids and solids. But I cannot venture to agree when I reflect that solidity, liquidity and gaseousness represent only an impermanent aspect of matter. The division of matter from the standpoint of the possibility of our sensations, has a firm root in our nature as cognising beings and has therefore a better rational footing than the modern chemical division into elements and compounds, which are being daily threatened by the gradual advance of scientific culture. This carries with it no fixed and consistent rational conception as do the definitions of the ancients, but is a mere makeshift for understanding or representing certain chemical changes of matter and has therefore a merely relative value. There are five aspects from which gross matter can be viewed. These are (1) sthūla (gross), (2) svarūpa (substantive), (3) sūkshma (subtle), (4) anvaya (conjunction), (5) arthavattva (purpose for use). The sthūla or gross physical characteristics of the bhūtas are described as follows:— Qualities of Earth—Form, heaviness, roughness, obstruction, stability, manifestation (vṛtti), difference, support, turbidity, hardness and enjoyability. Ap—Smoothness, subtlety, clearness, whiteness, softness, heaviness, coolness, conservation, purity, cementation. Tejas—Going upwards, cooking, burning, light, shining, dissipating, energising. Vāyu—Transverse motion, purity, throwing, pushing, strength, movability, want of shadow. Ākāśa—Motion in all directions, non-agglomeration, non-obstruction. These physical characteristics are distinguished from the aspects by which they appeal to the senses, which are called their svarūpas. Earth is characterised by gandha or smell, ap by rasa or taste, tejas by rūpa, etc. Looked at from this point of view, we see that smell arises by the contact of the nasal organ with the hard particles of matter; so this hardness or solidity which can so generate the sensibility of gandha, is said to be the svarūpa of kshiti. Taste can originate only in connection with liquidity, so this liquidity or sneha is the svarūpa or nature of ap. Light—the quality of visibility—manifests itself in connection with heat, so heat is the svarūpa of fire. The sensibility of touch is generated in connection with the vibration of air on the epidermal surface; so this vibratory nature is the svarūpa of air. The sensibility to sound proceeds from the nature of obstructionlessness, which belongs to ākāśa, so this obstructionlessness is the svarūpa of ākāśa.