THIS IS GAS WEEK.

Hokitika Guardian, 2 October 1924, Page 1

THIS IS GAS WEEK.

THE CASK OF THE HUMAN EYE. Since the introduction of the incandescent electric light, aching and fatigue of the eye has become a common complaint; and there can be little doubt that they are intimalcy associated. The question is naturally asked: “What is the best light to read by?” I!y many, perhaps the majoirty, the answer would be the “brightest.” Up to a certain point that would lie true enough. Hut mere intensity of illumination is not everythin". Though one limy compare the human eye with a camera, and say that the retina retina represents the senorti'.'.ed plate, there is this greatest difference between them. Once the plate has been exposed it is used up, nothing further happens. Rut let the sensitive retina be repeatedly over-exposed to intense light, not only does it become exhausted, but, because it i.s a living structure of extreme complexity and delicacy, ‘st.ruetii.ral changes set in. IL will inevitably became congested, and may iillimaloly drift into a condition to actual iiillaininatiuii that may permanently damage the sight. Of coursesuch a response i.s proportional to the degree and duration of the jlluminaiimi.

A brilliant Hash of lightning eatelling liie eye oil a dark liigliL with a widely dilated pupil. Hoods it with so intense a glare as to actually blind tlie person. Between such a ligbL as this, and that of a candle, there are tin immense number of graduations—• ami one lias to select I lie illumiuniiL that will not only exhaust the retina, but furnish it with the soft brilliance that alone can produce clear and coni* fortable vision. Let ns for a moment examine the nature of so-called white light. It i.s found to consist of a combination uf all the colours of the spectrum, associated at the red end of beat rays, and at the violet with actinic. rays, that is rays capable of inducing cliemieal changes nn a photographic plate. Until recently il was thought that these actinic rays were the dangerous rays In the electric light, but investigation lias shown Unit aiming the number of strong i 1 In ini nants enclosed in glass bulbs or tubes, the number of ultra-violet rays issuing was extraordinary few. The glass intercepted them almost entirely in all cases. And the lens of the eye lias a considerable power to do the same. Consequently, it was not altogether ill" aclinic power of these chemical rays that was doing I lie mischief, not the lew In-at rays, hut rather the simple brilliance of the illuminant. A series of photographs of the specha of a number of different varieties of light were taken, and the results proved exceedingly interesting. It was found that, the naked candle (lame emitted no violet or ultra-violet rays, neither did a naked oil llame. And the same result was found with the fish-tailed gas llame. The miked mantle burner showed about one-half violet, but no ultra-violet; the acetylene light much the same. Coining to another class of burner altogether, the electric incandescent, in ils glass bulb, whether Hie carbonised ccllulac filament. the metallic lilameiit in vacuo, or the intensely brilliant Osrnm light in its nitrogen tilled bulb, in mini* were till ra-vlolet l ays delected, and only a varyin ;> number ol violet. And yet tie- latlcr. when looked at direct R i. mm b (li.- one i ill it a t in;;.. It., high

temporal lire and intense brilliance are only possible in the presence ol sueli an inert gas as nitrogen. The unavoidable conclusion than seems to be that the irritating power nl these latter lighls must he due to their hard lirilliaoee only. The ideal illuniinanl should evidently be one that contains a lull quantile of the soft orange yellow of the spectrum. this could be best obtaineii from the oil lamp or gas burnt in a slightly yellow tinted mantle. The heat or diseloratioo power of the former would place it at a disadvanlage. It seems so iliHicult to accurately temper the light of an electric bulb and free it from its irritating and exhausting power, that the gas llame properly protected will eventually prove the safer.

Dull partieiilars as ta gas lighting and appliances for heating, cooking and power purposes may ho obtained from Mr Shannon, Moved Street, where may be obtained on the time payment system.