Description of a Totally Reflecting Prism. 277 



instrument exhibited for medical examinations, but the reverse; 

 and of this I speak from sufficient experiment. 



The Society will understand that whilst this instrument is 

 constructed so as to afford the utmost amount of light which 

 the dimensions of the passage of the ear can admit, it is not 

 intended to supersede the use of the speculum which generally 

 bears Dr Kramer's name, the utility of which, in so far as 

 that extends, is established by the concurrent experience of 

 the profession ; neither in th« other applications of prismatic 

 illumination which present themselves to me, would I be un- 

 derstood to depreciate existing apparatus, when I suggest 

 such modifications as may increase or extend their efficiency. 

 Indeed, it has been my aim, in constructing the other adapta- 

 tions of the prism, to frame these so as to be a ready appen- 

 dage of all the different forms of specula in the hands of the 

 profession. The importance attached by professional persons 

 to the existing very imperfect methods of illuminating the 

 ear may be estimated by a reference to Dr Kramer's Treatise 

 on the Ear, translated by Dr Bennet, which describes his in- 

 genious efforts to effect this end in these terms. " In order 

 to obviate the above objections (to all other forms of illumina- 

 tion) as far as possible, 1 have constructed the following appa- 

 ratus. The principal part is an argand lamp, with a thick 

 cylindrical wick, the reservoir of oil being placed behind the 

 box next to be described. This box is constructed of tin- 

 plate, the inner surface of which is painted black in order to 

 prevent any reflection of the light. It covers the lamp so as 

 completely to enclose the flame, the lamp-glass passing through 

 an opening in the top. At a convenient distance from the 

 flame, and behind it, against the inside of the back of the box, 

 there is a plated concave mirror. In the anterior face of the 

 box there is inserted a tin tube fourteen inches in length, which 

 is likewise blackened inside, and each extremity is provided 

 with a double convex lens two inches and a half in diameter. 

 The argand lamp throws its powerful mass of light against the 

 concave mirror, whence the rays are reflected through the 

 first convex lens, along the tube and through the second con- 

 vex lens. The luminous rays are thus collected into an in- 

 tensely bright focus of the size of a shilling, at a distance from 



