A scientific gentleman, in a recent conversation, broached to us a theory of taste and smell, which, so far as taste is concerned, is, we think, new. A similar theory in regard to smell has been propounded by Piesse, and is, we think, the true one. The theory of odors hitherto accepted, has been, that invisible particles, emanating from bodies, and coming in contact with the olfactory nerves, produce the sensation of smell. Substances to be odoriferous, need, therefore, to be volatile to a certain extent. Taste, says one author, " is merely a more delicate kind of touch." The nerves of the whole interior of the mouth are the ones supposed by some to be endowed with this " delicate touch," while others limit the nerves of taste to certain parts of the mouth, of which the tongue is chief. In general, sub-Stances insoluble in the fluids of the mouth, are regarded as being destitute of taste* The nerves of special sensation have been a subject of most profound study on the part of physiologists, who have never yet been able to find in their anatomy or composition anything to account for their peculiar functions. Knowledge bearing upon the subject, therefore, relates principally to the external phenomena of special sensation, and it is to these that the theory of which we write entirely pertains. The phenomena of sound have all been referred to vibrations of sonorous bodies, transmitted to the complex mechanism of the ear, by solid, liquid, or gaseous media, or a combination of such media. The phenomena of sight are also referred to vibrations of luminous bodies, transmitted to the eye by a medium called ether. In these sensations actual contact of the body, which is the primary cause of them, is known to be unessential. The new theory of taste and smell brings these sensations also into the category of impressions produced by vibration. In other words, these sensations are attributed to vibratory motions in external bodies, a knowledge of which is communicated to the mind through the nerves oi taste and smell, in a manner analogous to that in which im pressions caused by light and sound, are transmitted to the mind. In the case of taste, it is possible that no medium ex ists that can convey its impressions; the communication o: such impressions must, if this be the case, be immediate, thai is, the tongue must touch, in the popular sense, the thin tasted. There are, however, difficulties connected with this hypothesis, viz.: How are we to account for the absence o: taste when insoluble substances are placed on the tongue' How, if fine division and intimate contact with the nerves o: taste is essential to this sense, are we to account for the ab sence of taste when certain gases are taken into the mouth ? Certainly, in the latter case, we have the minutesjb subdivision ind as perfect contact, as is physically possible to obtain. It becomes evident, then, that there are bodies incapable of affecting this sense, as there are bodies which are non-luminous bo the eye, and others which, to the ear, are deficient in sonor-Dusness. But, supposing no known medium to be able to convey impressions of taste to the nerves of that sense, the theory of vi-Drations does not, on that account, become untenable. We are far from believing, however, that the subject has been studied sufficiently to pronounce with certainty upon this point. The corpuscular theory of light has been discarded as failing wholly to account for optical phenomena. In like manner have the theories of phlogiston and caloric successively given way to more enlightened views. Both light and heat are now considered as modes of motion. If now we retain the corpuscular hypothesis for the sense 3f smell, we suppose that to be the most delicate of all the senses, for by it we may, without artificial help, detect quantities of matter so small that they can be detected by no other sense, even though aided by the most powerful instruments science has been able to devise or art to construct. If we consider the act of smelling as only a more delicate kind of touch, as it has hitherto been thought, we suppose the power of sensation in the olfactory nerves infinitely superior to any others. Some illustrations will make this appear in a stronger Light. A grain of musk exposed for six months in a large room, communicates its odor to all the bodies in the room, witJwut any sensible loss of weigM. If a handkerchief thus perfumed with musk, be exposed to the most critical examination by the microscope, no musk can be detected deposited in its fibers. But, it may be said, the odoriferous principle exists in a gaseous state. If this were so, it might be reasonably supposed that delicate chemical tests would afford a trace of its presence, but they do not. Does not, then, the vibratory theory conflict less with the facts in this case than the theory of emanations ? The only grounds we have upon which to base the hypothesis of emanations is a sensation produced, and we have the same ground for believing that light and heat are emanations. But, it may be asked, how can the smell in the handkerchief be accounted for if the musk be not present ? To this it is answered, in the same way that sensible heat in a body is accounted for, after it is removed from a contact with another heated body, or fluorescence in bodies after exposure to sunlight. These phenomena are referred to the continuance of vibrations in bodies after the exciting cause is removed. It does no violence to analogy to suppose the same cause as con. tinuing the effect of an odor, after the primary cause is removed. A bar of block tin, when rubbed, emits a peculiar smell. No test, however delicate, can demonstrate the presence of metallic particles in the air or of the oxide or salts of tin, in this experiment. Applying the same reasoning adopted in relation to sound, heat, and light, it is extremely difficult to believe that smell, in this case, in produced by actual contact. It is well known that perfumes blend harmoniously when combined according to a scale, which may be represented by a gamut, in which different odors correspond to different musical sounds; and the other analogies between smell and sound are indeed very striking, as is shown by Piesse, in his work on " The Art of Perfumery," second section. A wide field of study and experiment is here opened, and, we have no doubt, that in future works on physics, the subjects of odor and taste are destined to find a place by the side of heat, light, sound, and electricity.