Development of Knowledge of Radiant Energy as Applied to Medical Uses

Abstract

PRIMITIVE man evidently had some sort of idea of the importance of sunlight—the only form of radiant energy he recognized—in human health and welfare, for all primitive religions contained some element of sun worship. The Greeks and Romans prescribed empirically in many conditions the extensive application of sunlight. However, it is probable that most of their “sun bathing” represented merely a popular fad. Whatever scientific knowledge of the influence of radiant energy that may have been gathered among the ancient peoples was lost sight of during the medieval period, characterized as it was by almost complete disregard of all hygienic principles. The first recorded instance of any attempt to employ any kind of radiation in disease was made by John Gadsden, who treated small-pox patients—among them a son of Edward I—with red light to prevent scarring. This method seems to have been extensively practised by the Chinese and it is probable that Gadsden adopted it as a purely empirical procedure. In 1661, John Evelyn, in his “Fumifugiurn,” uttered a scathing denunciation of the practice of burning “sea coal,” which produced a dense cloud of smoke, However, his diatribe was probably prompted by æsthetic considerations rather than any scientific understanding of the unhygienic exclusion of sunlight. The first really scientific contribution to the problem of radiant energy was made by Newton in his careful study of the spectrum visible when a beam of sunlight was directed through a prism. However, his results were not understood or applied practically until a much later date, and Newton died without knowing that radiations fall into a series differing only in wave length and frequency. Some time later Römer determined that light travels at a finite velocity. In 1678, Huygens propounded the theory of wave propagation of light. In 1777, Scheele noted that chlorine was liberated from silver chloride in the violet region of the spectrum. Two years later Ingenhauss showed that the dissociation of carbon dioxide by green leaves under the influence of sunlight is a chemical effect and not, as previously supposed, due to heat alone. These results were not fully understood until, in 1801, Ritter announced the discovery of the ultra-violet region of the spectrum, basing his conclusions on observations similar to those of Scheele but overlooked by the latter. A year previously Herschel had noted that a thermometer hung just outside the visible limits of the red end of the spectrum was markedly affected, which led to the discovery of the infra-red or dark heat rays. The next few years witnessed the evolution of Grothus' law of photo-chemical absorption: “Only rays absorbed are effective in producing chemical change.”