﻿352 Dr. It. E. Dudgeon on Subaqueous Vision. 



a pair of spectacles fitted with lenses of that power we can see 

 near and distant objects when we are below the water (provided 

 it is perfectly clear) as distinctly as we can with the naked eye in 

 the air. 



But such spectacles are attended with the obvious defect that, 

 though they give perfect vision below the water, they completely 

 destroy vision except for objects within half an inch distance 

 above water ; and the swimmer would find it extremely 

 awkward to have to adjust his spectacles to his eyes every time 

 he dived, and remove them whenever he came to the surface. 

 Therefore, for practical purposes, it would be desirable to pos- 

 sess spectacles which, while giving perfect vision below water, 

 would offer no impediment to vision in the air. 



A consideration of the media (air and water) engaged in the 

 case of the anterior lens of the eye lost by immersion led me to 

 the solution of this problem. 



By causing the rays of light to pass through the water com- 

 pelled to assume a convex shape and transmitted through air 

 before reaching the eye, a lens of almost any required power 

 may be constructed. Our object would be attained by a reversed 

 air-meniscus (concavo-convex lens) formed by segments of thin 

 glass globes with radii of curvature corresponding to those of the 

 aqueous humour. But such a lens would be troublesome to 

 construct and too small for use; and the same object can be 

 attained by employing air-lenses of larger dimensions. I found 

 that two segments of a glass globe of somewhat less than 2 inches 

 diameter, arranged with their concavities outwards and united 

 round their edges by a ring so as to form a double concave air- 

 lens, when immersed in water, forced the water into the convexity 

 required for refracting the light to a focus of 1*8 inch. The con- 

 vergence of the rays thus produced is equal to that caused by 

 the aqueous-humour lens in air, and suffices to effect the short- 

 ening of the focus of the crystalline required to bring the image 

 to the retina, thus supplying the place of the extinguished lens 

 of the aqueous humour and restoring perfect vision below water. 



A pair of spectacles fitted with lenses of this description does 

 not materially interfere with vision in the air, and gives perfect 

 vision when we plunge below the water. I have constructed 

 air-lenses of similar power by arranging together segments of glass 

 globes of different diameters, as 1J inch with 2 J inches diameter, 

 If inch with 2 inches, and so on. I likewise found that good 

 vision below water is obtained by lenses of various powers ranging 

 between 1^ inch and 2 inches focal length, though probably the 

 best vision for both near and distant objects below water is ob- 

 tained by lenses of the power indicated above. With these, 

 small type may be read easily and distant objects distinctly per- 



