Mr. R. Moon on the Structure of the Human Ear. 369 



with which M. Roche's beautiful researches are connected. In 

 any case these drawings, which refer to four days, give the key 

 to a very curious enigma presented by the eclipses observed in 

 South America, in Chili, and in Brazil; I speak of the black 

 protuberances. They seem to me to be due merely to the dark 

 interval which exists for a few minutes either between two adja- 

 cent eruptions the plumes of which join, or between the ascending 

 column of an eruption and its plume falling on the side of it. 



" Thus to observe the protuberances with the spectroscope at 

 any hour of the day, even when the sun is near the horizon, it is 

 sufficient to open slightly the slit of the spectroscope. Perhaps 

 M. Zollner will succeed in seeing them all together as in an 

 eclipse, by using very large prisms and a slit curved as an arc of 

 a circle." 



XLIII. On the Structure of the Human Ear, and on the Mode in 

 which it administers to the Perception of Sound. ifyR. Moon, 

 M.A., Honorary Fellow of Queen's College, Cambridge. 



[Continued from p. 130.] 



IN my last paper I endeavoured to show : — 

 1. That the fact of the tympanal membrane being concave 

 outwards, coupled with its flexibility, adapts it as an agent for 

 the transmission to the sensorium of the motion arising from 

 rarefied waves, while the same concavity^ coupled with the in- 

 elastic and unyielding character of the membrane, forbids the 

 transmission of the motion arising from condensed waves. 



2. That if the ear yields to the impressions which rarefied 

 waves tend to produce upon it, an apparatus will be required by 

 means of which, after exposure to such waves, the membrana 

 tympani may be brought back to its original position, and the 

 organ generally be restored to its normal status; that the 

 muscles acting upon the bones of the ear are calculated to per- 

 form that office ; and that no other adequate function has ever 

 been assigned to them ; whence we may conclude that that por- 

 tion of the auditory apparatus has been contrived with exclusive 

 reference to the action upon the ear of rarefied waves. 



3. That when either the tympanal membrane or the malleus 

 or incus is wanting, or the latter of those bones is disconnected 

 from the other or from the stapes, then, under the influence of 

 rarefied waves, the oscillations between the vestibular and cochlear 

 fenestra? of the fluid in the labyrinth will still be maintained by 

 the alternate action, on the one hand of a difference in the ex- 

 ternal pressures upon the fenestra?, and on the other of the sta- 

 pedius muscle ; and that in this way a considerable power of 



