35 



thimble on one of the fingers. This deprived her of sight for ten days, 

 after which, having had a severe hysterical paroxysm, her vision re- 

 turned, but convulsive and hysterical sensations still remained, from 

 which she was not relieved till six weeks after. This case, which the 

 author conceives to be a proof that the electric fluid is capable of sus- 

 pending the functions of the optic nerve without altogether destroy- 

 ing them, suggested the idea of some further experiments, with a 

 view to ascertain whether electricity could be so applied, by artificial 

 means, as to destroy the power of contraction possessed by nerves. 

 The effects seemed to prove the negative ; but it is owned these ex- 

 periments were made under circumstances which did not inspire much 

 confidence. . 



It appears, in general, that these experiments, and the observations 

 deduced from them, materially illustrate an action or power inherent 

 in the nervous chords, capable of producing the symptoms which oc- 

 curred in the cases here related ; and that the once favourite hypo- 

 thesis of a nervous fluid, does not give a satisfactory solution of those 

 nervous agitations, which only proceed for some way in the course 

 of a nerve, and are there arrested without being allowed to proceed 

 to the brain. The disorder known by the name Tic Douloureux, is 

 given as an example of the manner in which spasmodic tremors are 

 propagated along the nerves. And a case of a locked jaw occasioned 

 by an injury to the thumb, is lastly mentioned, which corroborates 

 all that has been said concerning the first case mentioned in this 

 paper. 



The Bakerian Lecture. On the Mechanism of the Eye. By Thomas 

 Young.M.D.F.R.S. ReadNov.27,1800. [Phil.Trans. 180 1,^.23.] 



The copious contents of this lecture relate chiefly to the power pos- 

 sessed by the eye to accommodate itself to the perception of objects 

 at different distances, concerning wliich a variety of opinions have 

 been entertained. 



After some general considerations on the sense of vision, from which 

 it appears that though the extent of the field of perfect vision for each 

 position of the eye be not very great, yet there is reason to believe 

 that its refractive powers are calculated to take in a moderately di- 

 stinct view of a whole hemisphere : the author, aware how essential 

 it is in an inquiry of so delicate a nature to proceed upon solid, and 

 as far as possible incontrovertible grounds, delivers a set of dioptrical 

 propositions (eight in number), each accompanied by some scholia 

 and corollaries, from which he means to deduce the principal infer- 

 ences brought forward in the sequel of the lecture. 



The nature of these can only be here intimated by their different 

 enunciations, some of which may appear elementary, yet lead to 

 results of a less obvious nature. They are as follows; 1. In all 

 refractions the ratio of the sine of the angle of incidence to the sine 

 of the angle of refraction, is constant. 2. If between two refracting 

 mediums a third medium, terminated by parallel surfaces, be inter- 

 D 2 



