372 



Lieut. -Col, A. Strange on a new Theodolite 



to certain delicate cells which are attached to the under surface of the 

 membrana reticularis. From this circumstance alone it appears very 

 evident that these investigators had not suspected, much less discovered, 

 the fact that the rods are most exquisitely graduated, for otherwise they 

 could surely never have doubted that so beautiful and suitable an appa- 

 ratus could have any other ostensible purpose than that of appreciating 

 the various sounds. I consider, indeed, that the cochlea represents a 

 musical instrument, similar in nature to a harp or musical box, the strings 

 of the one and the teeth of the other being represented by the rods of 

 Corti. The spiral bony lamina is simply a sounding-board ; around the 

 rods are placed the various nerve-cells and nerve-fibres, and from these 

 cells the impressions are conveyed by the fibres to the brain itself. 



It is possible, therefore, to trace very completely the course of sounds 

 or vibrations from a musical instrument or any other source to the brain, 

 through the medium of the ear. First the vibrations are caught and col- 

 lected by the auricle, and transmitted through the external' meatus to 

 the drum of the ear, next across the middle to the internal ear. Here the 

 sound is appreciated, merely as a sound, by the vestibule ; the direction is 

 discovered by means of the semicircular canals ; but to distinguish the 

 note of the sound, it must pass on to the cochlea. The vibration there- 

 fore passes through the fluid of the cochlea and strikes the lamina spiralis, 

 which intensifies and transmits the vibration to the system of rods. There 

 is doubtless a rod not only for each tone or semitone, but even for much 

 more minute subdivisions of the same ; so that every sound causes its own 

 particular rod to vibrate, and this rod vibrating, causes the nerve-cells in 

 connexion with it to send a nerve-current to the brain. 



In conclusion, I feel it my duty to mention that I am greatly indebted 

 to Professor Rutherford, of King's College, for suggesting the investigations 

 which led to these results, as also for much valuable advice while pro- 

 secuting them in his laboratory at King's College. 



Addition to Lieut. -Col. A. Strangers paper " On a new Great 

 Theodolite to be used on the Great Trigonometrical Survey of 

 India, with a short Note on the performance of a Zenith- Sector 

 employed on the same work." (See p. 317.) 



(Received June 15, 1872.) 



Since my paper with the above title was read, it has occurred to me 

 that some particulars as to the weight of the instrument might interest 

 those engaged practically in Geodesical work. The following are the weights 

 of the main parts as separated for carriage : — 



