346 ANNUAL OF SCIENTIFIC DISCOVERT. 



execute it, after a certain time of life, without the assistance of glasses suited 

 to correct the gradual change of focus which the eye itself undergoes. Some 

 persons even in early life in childhood who have very acute sight for distant 

 objects, require the aid of slightly convex glasses, to enable them to sustain, 

 for any considerable time, the effort of observing minute objects which are near 

 them. This assistance is still more frequently necessary in adults who have 

 passed the age of fifty. "With convex glasses, accurately adapted to their 

 peculiar focus, such persons are frequently able for many hours to follow their 

 occupation of needlework, when, without such aid, their sight would wholly 

 fail after a few minutes' application. In a like manner, short-sighted persons 

 suffer from attempting to work without suitable concave glasses. 



Dr. Caplin, of Manchester, says : If we take the trouble to investigate the 

 effect of light on the eye, we shall find that it is not so injurious as it is gene- 

 rally thought. An organ, whatsoever rt may be, is not injured so long as it 

 can perform its functions with facility. The stress on the eyes results from 

 want of light, and whenever the light falls on the object we want to see, and 

 not on the eyes themselves, it does not prove hurtful. I have known many 

 persons accustomed all their lives to most minute work, such as engraving, 

 whose eyes were neither affected nor impaired. This fact is in accordance 

 with the law of physiology, by which the strength of an organ is in propor- 

 tion to its activity. Oblique and bad light are the cause of affection. But it 

 may be remedied by altering the window, or changing the place or position 

 of the worker. The question whether the eye or any of the other organs of 

 sense, is capable* of improvement in proportion to its use, or whether like a 

 human mechanical contrivance it wears out by employment, is a very serious 

 one. A great deal of our conduct in daily life depends on the way we answer 

 it to ourselves. It is probable that the " wearing out" contrasted in the 

 popular saying, with "rusting out,' is often falsely attributed to the human 

 body, and that perfectly healthy organs are made more efficient by use pro- 

 vided that such use does not diminish the nutrition of the system ; but at the 

 same time local injury is certainly experienced in many parts of the body, 

 especially the eye, by working too long hours. The explanation appears to be 

 this, viz., that after the body has been long employed, sufficient vigor does 

 not remain in each separate organ to enable it to do its duty it can not be 

 called healthy after the general strength is exhausted. Overworking the eyes, 

 means working with the eyes in an unnatural condition. 



In using artificial light, the light should be above the level of the face, so 

 as to allow, as in nature, the brow, the lashes and the iris to shelter the pupil, 

 and thereby the expansion of the optic nerve from the direct rays. Neglect 

 of this precaution is injurious in two ways : first, the influx of such rays con- 

 tinued for a considerable period tends to exhaust the normal susceptibility of 

 the retina ; and, secondly, by eclipsing the brilliancy of the rays reflected from 

 the work, so that the Avorkman is induced to increase the light to a degree 

 otherwise superfluous, dazzling and pernicious. 



The following suggestions have been made in regard to the prevention from 

 injury of the eyes from artificial light. 1. Color of the light. To fully under- 

 stand the olij set !> be attained, it is luc-wary to bear iu vnir.d that, duyii :..; it 



