416 



THE INDIA RUBBER WOk1.D 



March 1, 1921 



Glare may be caused by direct reflection from shiny surfaces, 

 as well as by direct rays from light-sources. 



SCATTERED LIGHT IN THE EYE 



Let us once more return to our photographic analogy. If the 

 camera bellows leaks light a foggy negative is the result. Scat- 

 tered light in the eye interferes with clear vision also. This' 

 trouble is often confused with glare. The shutter of the eye- 

 camera, the eyelid, is very dilTerent from the photo camera shutter, 

 as we have before remarked, in being highly translucent, and 

 thereby admitting a considerable volume of diffused light when 

 closed. It is as if the camera shutter were made of ground 

 glass. Light-sources anywhere in front of the eye therefore 

 produce some extraneous light within, regardless of the direction 

 in which eye is looking. 



The final object of industrial lighting is to facilitate labor. 

 The individual capacity for performing any given labor depends 

 upon .skill, which may be defined as the ability to coordinate 

 muscular movement with the mental processes of perception and 

 judgment; to a certain degree upon muscular strength; upon what 

 the p.sychologist calls the "attitude," and upon the state of 

 fatigue, muscular and mental. The most efficient lighting is 

 therefore the kind that afTords the quickest and clearest per- 

 ception, and produces the least muscular and mental fatigue. 

 The subject of fatigue as related to illumination is mostly un- 

 explored territory as yet. There has been much loose tak about 

 "eye strain," as there has about "glare"— the two bugbears of 

 "illuminating engineering." Eye strain is muscular strain, and 

 has nothing to do with retinal fatigue. There are two important 

 sets of muscles connected with the eyes, one that does the focus- 

 sing, and the other that keeps the two eyes so aimed that the stereo- 

 scopic effect, i. e., binocular vision, is produced. When these are 

 overworked, more or less serious results follow, ranging all the 

 way from slight discomfort to nervous indigestion, and insanity. 

 Optical defects uncorrected by glasses are the most common 

 and serious in results; but defects in illumination may produce 

 marked discomfort. Optical defects in the eye, uncorrected by 

 glasses, are the most common cause of this complaint. The grow- 

 ing practice of industrial establishments of maintaining a regular 

 optical department, and examining and prescribing for the eyes of 

 all employes, is not a piece of philanthropy, but a most profitable 

 business investment like a good lighting installation. That light- 

 ing conditions which interfere with the normal action of the 

 visual organs induce a degree of general fatigue that plainly 

 reduces the output of labor, there is ample proof ; the exact 

 scientific relation of cause and effect needs much further experi- 

 mental research to reduce it to definite laws. 



SUlVtMARY 



The organs of vision consist of the eye (eye-ball), the optic 

 nerve, connecting the eye with the brain, and certain portions 

 of the brain in which the effects of light are translated into 

 sensations of vision. The mutual actions of these organs belong 

 to the science of psychophysics. 



The eye is an optical instrument similar to a photographic 

 camera, consisting of lens, stop, shutter, dark-box, and sensitive 

 film. The lens forms an image on the sensitive film (retina). 



The image on the retina is "developed" into the sensation we 

 call "seeing" by a mental process in the brain. 



The retinal image is the thing we actually see ; and vision can 

 be no clearer than this image. 



The lens of the eye is incapable of focussing different colors 

 sharply at the same time, i. e., is not an achromatic lens. It 

 can therefore produce a perfectly sharp image only by light of 

 one color (monochromatic light). The nearer light comes to 

 this quality the sharper the image. 



Mercury-vapor light is the only light in commercial use that 

 is approximately monochromatic, and hence gives greater acuity, 

 or sharpness, of vision than ordinary light. 



The retina, or sensitive film of the eye, has two kinds of 

 sensitive surface, one that sees colors and gives sharp vision, 

 the other that does not give colors but is used for seeing in dim 

 light. It requires a period of time up to a half-hour for the eye 

 to adjust itself for differences of light from very bright to 

 very dim. 



The eye can see by green light of miuii lower intensity than 

 with any other or all colors. 



Glare is the effect of discomfort and blurred vision resulting 

 from excessive contrast in brightness between different parts 

 of the field. It increases with the quantity of light entering the 

 eye and diminishes with the size of the bright spot. It is greatest 

 when the bright spot is looked at directly and is said to cease 

 when the spot is at an angle of more than 26 degrees from 

 the axis of vision. 



Scattered light within the eye interferes with clear vision 

 and may result from bright light-sources anywhere in the field. 



Eye strain is the result of overtaxing the muscles of accommo- 

 dation (focussing) and the muscles of fixation (those which hold 

 the eye in position to see the desired object). 



In the next issue we shall take up the application of the 

 theory to practical cases of lighting in rubber factories. 



RUBBER TRADE INQUIRIES 



nrriE inquiries that follow have already been aiistvered: never- 

 ■• theless they are of interest not only in sho'mng the needs 

 of the trade, but because of the f'ossibiliiy that additional in~ 

 formation may be furnished by those zvho read them. The Editor 

 is therefore glad to hare those interested communicate Zi-ith him. 



(847) A reader asks for the addresses of manufacturers of the 

 following: Rubber plugs for pencil tip erasers; metal sleeves to 

 hold plugs ; machine for clamping on metal sleeves. 



(848) A manufacturer requests the name of the manufac- 

 turer of the rubber substitute known as "Rubberaid." 



(849) .^n inquiry has been received for "rubber glass." a wire 

 mesh covered with several thicknesses of rubber, used extensively 

 by mining companies. 



(850) A concern with salesmen calling on the drug and hard- 

 ware stores, having 15,000 dealers handling its nationally adver- 

 tised product, desires to secure the selling rights or manufacturing 

 and selling rights on an additional meritorious specialty that can 

 be merchandised to the drug and hardware trade, preferably on a 

 royalty basis. 



TRADE OPPORTUNITIES FROM CONSULAR REPORTS 



.Addresses may be obtained from the Bureau of Foreign and 

 Domestic Commerce, Jp'ashington, D. C, or from the folloiving 

 district or cooperative offices. Requests for each address should 

 he on a separate sheet, and state number. 



District Offices. Cooperative Offices. 



New York; 734 Customhouse. ("leveland: Chamber of Commerce. 



Uoston: 1801 Customhouse. Cincinnati; Chamber of Commerce; 



Chicago: 504 Federal BuildinR. < General FreiRht Apent. Snuthcrn 



St. Louis: 402 Third National Bank Railway. 96 Ingalls CniKlini;. 



Building. Daytt-n. Ohio: Dayton Chamber of 



New Orleans: 1020 Tlibernia Bank Commerce. 



liuildinp. Los .^nKeles: Chamber of Commerce. 



San Francisco: 307 Customhouse. Philadelphia: Chamber of Commerce. 



Seattle: 848 Henry Building. Portland, Oregon: Chamber of Com- 

 merce. 



(34,367) A commercial agent in Egypt is planning to open 

 show rooms for the exhibition and sale of tractors, trucks, tires, 

 etc., and desires to secure the representation of firms with a view 

 to advertising and selling American goods. 



(34,409) A commercial agency in Ceylon desires to .secure the 

 representation of manufacturers for the sale of insulated wire. 



(34,433) A mercantile company in the Straits Settlements de- 

 sires to secure an agency for the purchase of rubber. 



