262 OF SENSATION, AND THE ORGANS OF THE SENSES. 



original sound, so as greatly to increase its intensity ; and the same sound- 

 board will act equally well for tuning-forl^s of several different degrees of 

 pitch. When a smaller body is used for resonance, however, it is essential 

 that there should be a relation between its fundamental note and that of the 

 sonorous body; otherwise no distinct resonance is produced. Thus, if a 

 tunino-fork in vibration be held over a column of air in a tube, of such a 

 length that the same note would be given by its vibration, its sound will be 

 reciprocated. And if it be held over a pipe, the column of air in which is a 

 multiple of this, the column will divide itself into that number of shorter parts 

 each of which will reciprocate the original sound, and the total action will be 

 one of resonance. But if the length of the pipe bear no such correspondence 

 with the note sounded by the tuning-fork, no resonance is given by the column 

 of air it contains. 3. Vibrations of conduction are the only ones by which 

 sounds can strictly be said to be propagated. These are distinguishable into 

 various kinds, into which it is not requisite here to inquire. It should be 

 remarked, however, that all media, fluid, liquid, or solid, are capable of trans- 

 mitting sound in this manner, a vacuum being the only space through which 

 it cannot pass. The transmission is usually much more rapid through solid 

 bodies than through liquid ; and through liquid than through gaseous. The 

 greatest diminution in the intensity of sound is usually perceived, when a 

 change takes place in the medium through which it is propagated, especially 

 from the aeriform to the liquid. 



354. The detailed application of these principles has been most elaborately 

 worked out by Miiller; and the following statement of what may be regarded 

 as the present condition of our knowledge of the subject, is little more than an 

 abstract o his results. Considering it desirable, in the first place, to establish 

 the conditions under which those animals hear, that are constantly immersed 

 in water, he made a series of experiments, from which he draws the following 

 conclusions : i. Sonorous vibrations, excited in water, are imparted with con- 

 siderable intensity to solid bodies. n. Sonorous vibrations of solid bodies are 

 communicated with greater intensity to other solid bodies brought in contact 

 with them than to water ; but with much greater intensity to water than to 

 atmospheric air. in. Sonorous vibrations are communicated from air to water 

 with great difficulty, with very much greater difficulty than they are pro- 

 pagated from one part of the air to another ; but their transition from air to 

 water is much facilitated by the intervention of a membrane extended between 

 them. iv. Sonorous vibrations are not only imparted from water to solid 

 bodies with definite surfaces, which are in contact with the water, but are also 

 returned with increased intensity by these bodies to the water ; so that the 

 sound is heard loudly in the vicinity of those bodies, in situations where, if it 

 had its origin in the conducting power of the water alone, it would be faint. 

 v. Sonorous undulations, propagated through water, are partially reflected by 

 the surfaces of solid bodies. vi. Thin membranes conduct sound in water 

 without any loss of its intensity, whether they be tense or lax. From m., iv., 

 and vi., we learn the mode in which the sound is conducted to the ear, in 

 aquatic animals not breathing atmospheric air. The labyrinth of such is 

 either entirely enclosed within the bones of the head, as in the Cephalopoda, 

 and in the Cyclostome and Osseous Fishes ; or, its cavity being prolonged to 

 the surface of the body, it is there brought into communication with the con- 

 ducting medium, by means of a membrane, besides receiving the vibrations 

 through the medium of the solids of the body, as is the case in Cartilaginous 

 Fishes and Crustacea. It would seem as if, in the Osseous Fishes, the reso- 

 nance of the cranial bones, in which the labyrinth is imkrdded, were sufficient 

 to give the requisite increase of intensity to the sound ; whilst in the Cartila- 

 ginous orders, the softness of these bones renders some other means necessary. 



