Physics of the Terrestrial Environment, Subtle Matter and Height of the Atmosphere: Conceptions of the Atmosphere and the Nature of Air in the Age of Enlightenment

The discovery, in the middle of the 17th century, of both the weight of air and the law governing its elasticity transformed the status of the atmosphere from that of a purely mathematical object to that of a complex and highly variable physical system. In the context of rapidly intensifying experimentation and observation, the nature of the atmosphere was therefore the subject of a host of hypotheses, which 18th century scholars tried to reconcile with a coherent physical approach. In particular, this was achieved by the conceptualization of invisible or “subtle” materials, thought to be closely linked to atmospheric stratification. Subtle matter was introduced, largely to reconcile contradictory results concerning the estimation of the height of the atmosphere. These estimations were based on different methods, mainly using the observation of meteors and the refracted and reflected light of stars. Taking as its common thread the question of the height of the atmosphere, which was omnipresent in the texts at the time, this book traces the history of the discovery of the atmosphere and the many questions it generated.

Table of Contents:
Introduction ix Chapter 1. Words Used to Describe the Atmosphere and Subtle Matter 1 1.1. Introduction 1 1.2. Air and the atmosphere 3 1.3. Vapors and exhalations 13 1.4. Coarse and subtle matters 21 1.5. The triptych of heat, fire and light 25 1.5.1. Heat 25 1.5.2. Fire 29 1.5.3. Light 31 1.6. Ether 35 1.7. Fundamental properties of air 37 Chapter 2. Refractive Matter 41 2.1. Introduction 41 2.2. State of knowledge in the 17th century 42 2.2.1. Representations of the atmosphere in the mid-17th century 42 2.2.2. The atmosphere of mathematicians and refraction in the first half of the 17th century 48 2.2.3. Gravity and elasticity of atmospheric matter in the second half of the 17th century 50 2.3. Arguments for the introduction of a refractive matter other than air 54 2.3.1. Argument based on invalidation by the observation of the theory of refraction by vapors and exhalations 54 2.3.2. Argument based on the high values of horizontal refraction at high latitude 58 2.3.3. Argument based on the too large value of the horizontal refraction predicted by the barometric model 63 2.3.4. Argument based on the gap considered as too large between the refractive height and the heights determined by the other methods 64 2.3.5. Argument based on the judgment that the sine law implies an absurd consequence on the path of light rays 67 2.4. Discussion 69 2.4.1. Observers and refractive matter 70 2.4.2. Cartesians and refractive matter 73 2.4.3. Mathematicians and refractive matter 76 2.5. Conclusion 78 Chapter 3. Solar Matter 81 3.1. Introduction 81 3.2. State of knowledge of the Sun in the 17th century 82 3.2.1. Sunspots and rotation of the Sun on its axis 82 3.2.2. Nature and origin of comets and their tails 87 3.2.3. Zodiacal light and solar atmosphere 95 3.2.4. The example of Hartsoeker’s model merging sunspots, comets and zodiacal light in a single representation 99 3.3. Solar matter and height of the atmosphere 103 3.3.1. Solar atmosphere and effect on the duration of twilight 104 3.3.2. Solar atmosphere and the Northern Lights 106 3.4. Conclusion 118 Chapter 4. Magnetic Matter 121 4.1. Introduction 121 4.2. Main concepts of magnetism in the 17th century 121 4.2.1. Descartes’s magnet theory and Gassendi’s design 121 4.2.2. Knowledge of magnetism at the turn of the 18th century 129 4.3. The explanation of the aurora borealis by magnetic matter 139 4.3.1. The aurora borealis of 1716 and the hypothesis of Edmond Halley 139 4.3.2. The consequences of Halley’s hypothesis 143 4.4. Magnetism in the second half of the 18th century 151 4.5. Conclusion 157 Chapter 5. Electrical Matter 159 5.1. Introduction 159 5.2. Highlighting the link between electricity and thunderstorm activity 162 5.2.1. The first experimental advances 162 5.2.2. Characterization of the natural electricity of the atmosphere 165 5.3. Knowledge of the nature of electricity in the mid-18th century 171 5.4. Precursory work on fiery meteors 173 5.5. Explanation using electricity 177 5.5.1. Early stages 177 5.5.2. Theories based on electricity 181 5.5.3. Controversies about the explanation by electricity 186 5.6. Elucidation of the origin of fiery meteors and falling stars 192 5.7. Conclusion 196 Chapter 6. Subtle Air 199 6.1. Introduction 199 6.2. Difference in mercury heights between different barometers 201 6.3. Suspension of water and mercury from the tops of inverted tubes 203 6.4. Gravity theories and the impulse system 215 6.5. Light barometers 227 6.6. Conclusion 235 Chapter 7. Results and Theories on the Height of the Atmosphere in the 18th Century 237 7.1. Introduction 237 7.2. Representation of the atmosphere inherited from previous centuries 238 7.2.1. Representation of the atmosphere 238 7.2.2. The central question of the height of the atmosphere 241 7.3. Two major paradigms for the composition and vertical extension of the atmosphere in the 18th century 244 7.3.1. A lower atmosphere heavily laden with vapors and exhalations 244 7.3.2. An upper atmosphere extended upwards, but how far up? 248 7.4. The three main inconsistencies between estimates of atmospheric height made by different methods 253 7.4.1. First inconsistency: twilight duration and atmospheric refraction 253 7.4.2. Second inconsistency: atmospheric refraction and air pressure 256 7.4.3. Third inconsistency: air pressure and aurora borealis 259 7.5. Two other methods for estimating the height of the atmosphere 268 7.5.1. Fiery meteors and falling stars 268 7.5.2. Projection of the Earth’s shadow during lunar eclipses 270 7.6. Conclusion 270 Chapter 8. Atmospheres of Earthly Bodies 275 8.1. Introduction 275 8.2. Porosity of bodies 279 8.2.1. Boyle’s founding treaty 279 8.2.2. Musschenbroek’s theory inherited from Newton 282 8.2.3. Nollet’s experiments on porosity 285 8.3. Atmospheres of bodies 290 8.3.1. The atmosphere of solid bodies according to Boyle 290 8.3.2. Mariotte’s aerial matter 291 8.3.3. Nollet’s distillation experiments 295 8.3.4. Atmospheres of liquid bodies and ice formation according to Perrault 297 8.3.5. Béraud’s atmosphere of electric and magnetic etheric matter 299 8.3.6. Marat’s igneous and luminous atmospheres 305 8.4. Conclusion 318 Conclusion 321 References 323 Index 337

About the Author :
Eric Chassefiere is a physicist and member of the SYRTE History of Astronomical Sciences Team, France. As Director of Research at the CNRS, he conducted most of his research on the study of non-terrestrial atmospheres through space observation and modeling. As a Professor at the École Polytechnique, he has led courses on the physics of the Earth and its atmosphere.