630 PHILOSOPHICAL TRANSACTIONS. [ANNO 1800. 



the impressions of sound, and to proportion them to the powers and expectation of 

 the organ. Mr. P — had lost this power for a considerable period after the de- 

 struction of the membrane ; but in process of time, as the external ear acquired the 

 additional motions I have described, sounds were rendered stronger or weaker by 

 them. When therefore he was addressed in a whisper, the ear was seen immedi- 

 ately to move ; but when the tone of voice was louder, it then remained altogether 

 motionless. 



Some additional Remarks to the foregoing, on the Mode of Hearing in Cases where 

 the Membrana Tympani has been destroyed. By Evd. Home, Esq. p. 159. 



After having communicated to the r. s. the curious facts contained in Mr. 

 Cooper's paper, which prove that the organ of hearing is capable of receiving all the 

 different impressions of sound, when the membrana tympani has been destroyed, it 

 may not be improper to explain, from the observations contained in a former paper 

 on this subject, in what manner this may take place. It is there stated, that any 

 vibrations communicated directly to the bones of the skull, are as accurately im- 

 pressed on the organ, as through the medium of the membrana tympani. The 

 office of that membrane is therefore to afford an extended surface, capable of re- 

 ceiving impressions from the external air, and of communicating them to the small 

 bones of the ear ; which a membrane would be incapable of doing, unless it had a 

 power of varying its tension, to adapt it to different vibrations. 



In the above cases, in which this membrane, the malleus, and the incus, had 

 been destroyed, it would appear that the stapes was acted on by the air received into 

 the cavity of the tympanum, and communicated the impressions immediately to the 

 internal organ. This not happening for some months after the membrane was de- 

 stroyed, probably arose from the inflammation of the tympanum confining the 

 stapes, and rendering its vibrations imperfect. That sounds can be communicated 

 with accuracy by the bones of the skull, to the internal organ, when received from 

 solid or liquid substances, has long been well understood. That the membrana 

 tympani is incapable of perfectly answering this purpose, when sounds are propa- 

 gated through air, has been a generally received opinion ; to refute which, was the 

 object of my former paper. That in cases in which the membrana tympani has 

 been destroyed, the air is capable of acting with sufficient force on the stapes to 

 communicate vibrations to it, and to produce on the internal organ the necessary 

 effect for perfect hearing, is completely ascertained by Mr. Cooper's observations. 



IX. Experiments and Observations on the Light which is Spontaneously emitted, ivith 

 some Degree of Permanency, from various Bodies. By Nath. Hulme,* M. D., 

 F.R.S. and A.S. p. 161. 



The discoveries which have been made with respect to light, as it proceeds im- 

 * Dr. Hulme was a native of Yorkshire, where he was born, in 1732 j and he died in the Charter- 



