millions of people make regular pilgrimages debating legion mountain peaks and other places especially favored by the sun seeking its health giving back in ancient times people reverence the in this bit of sculpture over thirty three hundred years old our king and his family seated in the sun to demonstrate the vital power of the sun's rays the sculptor carved the word life at the ends of some of the be prize the healing power of the son they build as part of their houses the solarium where some balance could be taken regular who was sure that there was more to sunlight than meets the eye so he tracked the sun baked and passed it through a prism and there were the colors of the rainbow the component parts of white li that was way back in sixteen hundred sixty six those things and sun worshippers must have seen many rainbows but they never associated this are inspiring display with the breakdown of sunlight but the spectrum which newton unfolded the red orange yellow green blue and violet were not all of the rays of sunlight they were only the v that portion of sunlight which the human eye can see in one thousand nine hundred the great english astronomer herschel discovered the long invisible red rays which transferred more heat  in the following year the noted german physician rather discovered the shorter and mark chemically powerful ultraviolet rays at the other end of the spectrum infra red ultra violent we can see them how do we know they exist well here for instance as a whistle not just an ordinary whistle it's a dog whistle which creates sound waves pitched to hide to be heard by the human  the length of a wave being the distance from the crest of one wave to the crest of the next wave ocean waves are the longest which we see in nature these little ripples are also waves but there wavelengths are much smaller than the giant ocean waves but even these tiny waves are tremendous in size compared to the wavelengths of light which are so small that an entirely from the unit of measurement have to be developed the accepted unit of measurement of light visible light extends from seventy seven hundred angstrom units for the visible red down to thirty nine hundred for the visible violet but the invisible infrared raids go up into the hundreds of thousands while the invisible ultraviolet rays drop down to about one hundred angstrom units the existence of these raids had been known to science for more than one hundred fifty years but it wasn't until eight hundred seventy seven that a sensational discovery was made by two english scientists their discovery was the start of the great modern development of ultraviolet therapy these men exposed  tool but microscopic organisms to the sun they had them wrapped a second two containing organisms in black paper and placed it next to the first after several hours of strong sunlight they found that the covered two was alive with microscopic organisms while the exposed to was free of them this experiment plus others proved that it was the shark ultraviolet rays and only the ultraviolet ra which killed bacteria that is they were bactericidal but the ultraviolet rays of the sun could not be depended upon for unfortunately ultra via that's life as offered by nature is very changeable and unreliable it varies in different parts of the world different seasons of the year and different times of the day in addition and even more important most of the valuable rays are soaked up by the earth's atmosphere infrared heat rays get through the earth's atmosphere is early but only the few ultraviolet rays near the visible part of the spectrum reach the earth's surface and those few that do get through are further dissipated by the haze and smoke of modern industrial life even the glass in our homes and our modern clothes prevent us from getting any of the benefits of the sun's valuable ultraviolet rays in  a system of quartz lenses used courts because it is one of the very few unknowns substances which permits the transmission of all the ultraviolet rays he concentrated strong ultraviolet rays on small sections of disease skin and was able to clear up the horrible disfiguring lesions of lupus vulgaris a tubercular infection of the skin another great advance and ultraviolet therapy came at the end of world war one lacking cod liver oil dr hudgins ki a berlin physician exposed children's suffering from records to artificial ultraviolet rays in a few months these miserable little creatures with what bones flabby muscles and inflated bellies were changed back into fun loving children after this discovery ultraviolet therapy became standard treatment for records even at this late date however it was not yet known just why ultraviolet rays accomplish such remarkable results but in one hundred twenty four came the discovery of the important clue where john valle the mystery of the cure of records doctor's ha park working independently found that certain foods including milk became abby ricketty when irradiated that means exposed to ultraviolet light now it was known that cod liver oil irradiated skin and irradiated foods all cured records the question was what did these three charolais different methods have in common the answer came soon after it was vitamin d the vitamin which promotes the absorption of calcium and phosphorus so necessary for the building of strong bones and teeth by them and d is produced in plant and animal life by exposure to certain ultraviolet rays we know that green plant pigment chlorophyll is produced in plants only when they are exposed to sunlight keep a plant in the dark and the leaves lose that rich green color they become pale and the plant slowly dies did i sunshine to human beings and they also lose their healthy skin color they become pale listless and fall easy prey to disease what did sunlight do to keep plants and human beings healthy it was found that ultraviolet rays act on a substance in the leaves of plants and in the skins of animals this substance known as sterile is changed to vitamin d the vitamin d is picked up by the capillaries in the lower layer of the skin the ultraviolet rays also swell the capillaries so that the blood flows faster and more freely and carries the vitamin d throughout the body although these ultraviolet rays are absorbed only by the outer skin they affect the metabolism of our bodies the blood formation the digestive system the bone structure and the whole nervous system further experimentation and stablished the fact that the ultraviolet rays necessary to produce the reddening of the skin or area thema kill bacteria and your records fall in that light wave band between thirty one hundred m twenty three hundred angstrom units and this is the band of rays that became the goal for inventors of ultraviolet rays generators while the carbon are the first of these generators was useful for therapeutic purposes it had too many drawbacks to create the arc the electrodes had to be made to touch pulled apart to form the proper gap the formation of sparks and ash the high running expense due to its operation that's very high temperature and the nuisance of replacing burned out carbons pointed to the need for a better life the early quartz mercury arc was an improvement over the carbon arc its value diminished however with u c as the fused in metal electrodes deteriorated and formed a fine deposit on the inside of the courts too it was this deadly increasing deposit which gradually reduced the ultraviolet rays output through the courts until the electrodes eventually burned out entirely