being effected without changing the position of the head, and with only a very little motion of the fingers. The contrast is readily made, and the difference, if any, with facility discovered. If both limbs of the instrument be simultaneously employed, and if the difference in the amount of the same sound conveyed to the instrument be material, an absolute test is procured at once; for, as has been already explained, no sound will be heard in one ear, and a full sound will be heard in the other. For example, a musical box placed upon the banks of the Serpentine is heard in that ear which is supplied with that limb of the stethophone (an elongated one) whose cup is immersed in the river, and not at all in that connected with that limb whose cup is held upon the ground. In the same way this test of restriction of hearing to one ear, or of uno-aural hearing, is available for deciding upon the comparative acoustic value of different arrangements. If we desire for instance to know whether surrounding a glass with water and another with air both filled with water and previously being equal in communicating sound to the stethophone, gives a difference of sound, the fact is immediately made known. The ear connected with the limb of the stethoscope immersed in the glass surrounded with water hears nothing, while the ear connected with the glass surrounded with air has a distinct sensation. S. S. A. THE EMPLOYMENT OF WATER IN AUSCULTATION. [From the Medical Times and Gazette, July 2, 1859.] WHEN lately engaged in performing experiments upon the propagation of sound, I ascertained that water placed between the aperture of a hearing-tube and a solid sounding body, gave an increase to the sound conveyed to the ear without it, and that a sound so near as to be inaudible without water so interposed was made audible by the addition of this medium of communication. For example, a watch placed upon a table would be moderately well heard when listened to through a hearing-tube with its aperture placed immediately upon that table; but would be better heard when the aperture of the hearing-tube was placed in water lying upon the table; and the sound of a watch removed to some distance upon the table, though not heard by means of the EMPLOYMENT OF WATER IN AUSCULTATION. 415 aperture of the hearing tube placed directly upon this body, would be rendered audible by interposing water. The amount of increase of sound thus procured by the interposition of water is very considerable, and is such as very materially to add to the value of hearing tubes when employed upon the sounds of solid bodies. The increase of sound is very striking; an impression is made upon the mind as if the sound were proceeding from a body greatly larger than it really is; the sound is louder; it is also fuller and softer. If the sounding body be listened to through a double stethoscope, such as my differential stethophone or phonoscope, which has two apertures for conveying sounds separately to both ears; and if in the case of one of these apertures water be interposed, such is the increase of sound so produced, that the mind becomes conscious of the sound in that ear only, having the advantage of the interposed water. The mind now becomes unconscious of any sound in the other ear; although, previous to the employment of the water, the mind was perfectly sensible of it. This phenomenon forms a good test of the water having produced a stronger auditory sensation; for I have ascertained that the same sound conveyed in a major intensity to one ear sensorially nullifies a minor impression from the same sounding body conveyed to the other ear. This is the test of restriction of hearing to one ear, or of uno-aural hearing. The quantity of water which will give an increase of sound need not be more than a fine film under the hearing tube, and extensive enough to connect the entire circumference of the aperture with the solid sounding body. When water in such small quantity is employed, the increase of sound is made more obvious by holding the aperture of the hearing tube very lightly upon the solid body, and the result may be made still more remarkable by raising the edges of the aperture a very little from the solid body, taking care to preserve the water in contact with its entire circumference, and also in contact with the solid body, the water, in fact, being preserved in the shape of a ring, with one edge in contact with the hearing tube and with the other in contact with the solid body. In the case of sounds, such as those of a watch, a greater increase of sound is obtained by employing a large quantity of water, such as a tumblerful or a bowlful; but if a very great amount of water be employed, such as that in a large cistern, and the hearing tube be placed at one extremity and the sounding body at the other, no increase may be obtained, and indeed the sound may be rendered inaudible, for it is well remembered that sound diminishes in the ratio of the square of the distance, and water gives no exception to E.W.SC this law. For an increase of sound to be procured the diminution from distance must be less than the augmentation from the intensifying property of water. In the case of sounds, such as are produced by striking one large stone upon another upon the dry ground, an intensification of sound may be procured, although the water intervening may be many feet in extent. The increase of sound procured by the interposition of water varies much with the material of which the hearing tube is formed. Wooden and metallic plate tubes, such as are firm or non-flexible, receive no advantage from water; tubes such as the flexible stethoscope and ordinary hearing or speaking tubes acquire a material reinforcement from water, while tubes made of india-rubber gain a very great advantage from the interposition of this medium. It may be stated, as a general rule, that the more a hearing tube becomes a mere air instrument, and departs from the character of a solid conducting instrument, the more water adds to its acoustic value. When a tube, by means of firm solid walls, becomes more of a solid conductor of sound, water becomes less useful, till at last, as in the case of a wooden stethoscope with only a fine bore, it diminishes sound, and acts as a damper The construction of hearing tubes materially affects the results obtained from the employment of water. A tube which is provided with an ear-piece that enters the meatus externus serves to show the augmenting property of water EMPLOYMENT OF WATER IN AUSCULTATION. 417 more than one having a circular disc to cover the external ear. A cup or expanded extremity, for the collection of sound, serves likewise to increase the reinforcing power of water. The contraction of the tube beyond the cup to the uniform size of the external meatus favours the same result. Whatever interferes with the free undulations of the air contained in the tube reduces the property of water under consideration. If a piece of membrane of the greatest tenuity be stretched across the tube or bore of the instrument, between the cup or aperture and the aural extremity, the result is materially reduced. If a tube be converted into a solid body by closing up the hollow part, water far from increasing the sound heard, materially reduces it. A solid rod of wood, such as a ruler or a solid stethoscope, is deteriorated by water employed in the manner under consideration. The evenness or unevenness of the surface of sounding bodies materially affects the result obtainable from water when hearing tubes are employed. The augmentation of sound is much greater when the surface is rough and uneven, and thus prevents the exact fitting of the cup of the hearing tube upon it. The consistence of solid bodies naturally affects the result of the employment of water. The effect is greater in the case of hard resisting bodies, such as wood or stone, than of softer bodies, such as leather. The freedom or constrained position of the cup or the tube, in respect of capability of vibrating, very materially influences the action of water. If the cup be held firmly by the fingers the result is greatly deteriorated. If the cup be pressed to the bottom of a vessel containing water, the sound heard is greatly less when it is kept free in media aqua. In order that water shall augment sound in the manner under consideration, viz., from solid bodies through hearing tubes, it is necessary that the water come in immediate contact with the aperture of the tube, or be separated from it only by some thin movable or vibrating body, such as thin india-rubber, gutta-percha, or other membrane or other solid body which, in reference to the strength of the sound, shall be small and vibratory. A thin membrane offers little impediment in the case even of a fine delicate sound, but a thin layer of wood, the one fiftieth part of an inch in thickness, will materially counteract the augmenting power of water in the case of a fine sound, such as that of a watch or even of a tuning-fork. The more the intervening solid body is E E indisposed to vibrate, the more it interferes with the soundaugmenting property of water. For a layer of wood one twelfth of an inch thick, placed between the water and the hearing tube, to admit of the advantage of water being even in some degree manifested, the sound proceeding from the solid body beyond the water must be very loud and capable of violently agitating the water, and the wood placed between it and the hearing tube. Layers of india-rubber offer much less impediment to the augmenting power of water; these, in fact, act as membranes. Thin membranes offer no sensible impediment whatever. When hearing tubes are to be employed lower than the mere surface of water, and we desire to have the fullest possible amount of sound, it is necessary to close the lower aperture of the tube, so that the water shall not enter into the interior of the instrument. If this be not done no sensible increase of the sound is obtained by carrying the instrument lower in the case of a hearing tube of uniform diameter, or a simple cylinder, and a great reduction of the sound is observed in the case of a hearing tube which is provided with an expanded bell-shaped or other widened aperture, such as the cup extremity of the stethoscope. It is very different with tubes, whether cylindrical or expanding at the apertures, closed with membranes; for the more these instruments are sunk the greater is the amount of sound procured. The increase of sound procured by sinking such an instrument is very great, provided the solid sounding body be not far distant. In the experiments of M. Collodon, in the Lake of Geneva, in 1826, a cylinder of uniform diameter was employed, and it was closed at the bottom with tin, the same material of which the walls were constructed. It was three yards long and eight inches in diameter. This hearing tube was provided neither with a fine tube to pass into the ear, nor with an expanded extremity for the better collection of sound, so that as a hearing tube instrument it was very defective, having, besides, the disadvantage of a solid bottom. But in some of my experiments upon sound in water proceeding from solid bodies, I have employed an instrument having all the advantages of construction possessed by an ordinary hearing tube, viz., a cup, or expanded extremity or aperture, for collecting the diverging pulses, so to speak, of sound, and to converge them together; a narrow tube to carry these converged pulses, and an open extremity to pass into the external canal of the ear, so that the sonorous pulses, without suffering diminution by escape into the external air, should |