331 



Moreover, as a general rule, those substances that are most affected 

 in density by heat are the most sensitive. 



6. No sudden change of sensitiveness occurs near the boiling- 

 point ; at least this is true in respect to bisulphide of carbon, ether, 

 and methylic alcohol. 



XVIII. "On the Adaptation of the Human Eye to varying 

 Distances." By CHARLES ARCHER, Esq., Surgeon, Bengal 

 Army. Communicated by Prof. STOKES, Sec. R.S. 

 Received June 17, 1858. 



(Abstract.) 



The following is a summary of the author's views on the question : 



1 . The eye is adapted to varying distances principally by an alter- 

 ation in the fibrous arrangement of the lens itself. Moreover, that 

 when the lens is removed after an operation for cataract, the power 

 of adaptation is nearly lost, and can only be exerted within very 

 confined distances. 



2. That the purpose of focalizing light at short distances is doubt- 

 less assisted, as suggested by Bowman, by the contractions of the 

 ciliary muscle, in its antero-posterior direction, bringing forward the 

 ciliary processes. 



3. That as the posterior hemisphere of the capsule is firmly united 

 to the hyaloid membrane, this portion must always remain quiescent, 

 and therefore the antero-posterior contractions of the ciliary muscle 

 must be very limited as regards the lens. 



4. That the ciliary muscle, being placed around the eye, and its 

 fibres being of a somewhat plexiform character, the contractions of 

 the muscle will relax those yielding portions of the eye placed within 

 its circumference. 



5. That the relaxations of the ciliary processes will deprive the 

 capsule of its firm support. It will be pressed forward by the lens, 



