# How Infrared Radiation Was Discovered--Range of This Discovery and Detailed, Unknown Information
## 5 Interesting Facts  
The whole of his works, [PERSON] with truly metrological care and diligence published on over 500 pages in the journal \"Philosophical Transactions of The Royal Society of London for the Year MDCCC\", published in 1800 in three volumes. The journal was, then, a publication of the then British Academy of Sciences and was of a quatrain. In these publications, he described about 50 different measurement stands he built to study the properties of infrared radiation. This article contains only a small part of the description of his very carefully conducted experiments. It is interesting to note that in his articles he did not name the temperature scale he used. At that time there were 6 different types of thermometric scales in use. The most commonly used were the Fahrenheit scale (invented in 1724, \({}^{\circ}\)F) and the Celsius scale (invented in 1742, \({}^{\circ}\)C). There were also the Newtonian (invented in 1700, \({}^{\circ}\)N), Romer (invented in 1701, \({}^{\circ}\)Ro), Reaumur (invented in 1731, \({}^{\circ}\)Re) and Delisle (invented in 1732, \({}^{\circ}\)D) scales. The relationships that exist between these scales, together with the Kelvin (invented in 1848, K) and Rankine (invented in 1859, \({}^{\circ}\)R) scales created at a later date, are shown in Figure 9 [14]. The Celsius scale is part of the metric system of measurement established as an international standard of measurement in 1875 and became the official form of standardised measurement for most European countries and their colonies in the late 19 th century. Because the Celsius scale was the primary temperature scale of the metric system, it became the official temperature scale for most of the world. The only countries that abstained from adopting it were English-speaking countries such as Britain, India and South Africa. In these countries, the Fahrenheit scale was used. It was not until the middle of the 20 th century that English-speaking countries began to adopt the metric scale expressed in degrees Celsius. Currently, only three countries use the Fahrenheit scale. These are the United States, Liberia and Burma. Figure 8: Measurement stand for infrared radiation transmission test—original drawing of the measurement stand [12]. Considering the above, it can be assumed with high probability that [PERSON] used the Fahrenheit scale in his measurements. Additionally, the analysis of the shape of the curve, prepared by him, containing the distribution of the spectrum of visible light and thermal radiation (Figure 10), indicates that the experiments were conducted at the end of February or the beginning of March. Therefore, the ambient temperatures measured by [PERSON] at about 50\({}^{\circ}\) may indicate that he used the Fahrenheit scale in which the equivalent of 50 \({}^{\circ}\)F is about 10 \({}^{\circ}\)C (Figure 9) [14]. Figure 10: Spectral distribution of visible light and thermal radiation—thermal radiation on the left (A, S, Q, A represents the spectrum of heat), visible light distribution on the right (G, R, Q, G represents the spectrum of visible light)—original drawing from [PERSON]’s article [10]. Figure 9: Conversion of temperature scales [14]. It should be noted, however, that it is not essential here what temperature scale [PERSON] used, since in all his experiments, he operated with temperature increments rather than absolute values of the temperature. [PERSON]'s law makes it possible to calculate the radiant intensity of blackbody \(M(\lambda,T)\) for a given temperature \(T\) and wavelength \(\lambda\):  
\[M(\lambda,T)=\frac{c_{1}}{\lambda^{5}\cdot\left[\exp(\frac{c_{2}}{\lambda\cdot T })-1\right]}\ W/\,\mathrm{m}^{2} \tag{1}\]  
where:  
\(c_{1}=2\cdot\pi\cdot h\cdot c^{2}=(3.741832\pm 0.000020)\cdot 10^{-16}\ W \cdot\mathrm{m}^{2}\)--the so-called first radiation constant,  
\(c_{2}=h\cdot c/k=(1.438786\pm 0.000045)\cdot 10^{-2}\ \mathrm{m}\cdot\mathrm{K}\)--the so-called second radiation constant.