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## Historical and scientific commentary of Bošković's dissertation De aurora boreali (1738)

Historical and scientific commentary of Bošković's dissertation De aurora boreali (1738)

*// 20. Dani Frane Petrića / 20th Days of Frane Petrić*/ Zagorac, Ivana ; Martinović, Ivica (ur.).

Zagreb: Hrvatsko filozofsko društvo, 2011. str. 183-186 (predavanje, domaća recenzija, sažetak, znanstveni)

**Naslov**

Historical and scientific commentary of Bošković's dissertation De aurora boreali (1738)

(Povijesni i znanstveni komentar uz Boškovićevu raspravu De aurora boreali (1738))

**Autori**

Vujnović, Vladis ; Lisac, Inga ; Martinović, Ivica

**Vrsta, podvrsta i kategorija rada**

Sažeci sa skupova, sažetak, znanstveni

**Izvornik**

20. Dani Frane Petrića / 20th Days of Frane Petrić
/ Zagorac, Ivana ; Martinović, Ivica - Zagreb : Hrvatsko filozofsko društvo, 2011, 183-186

**ISBN**

0-553-67777-8

**Skup**

Od Petrića do Boškovića: Mijene u filozofiji prirode / Petrić to Bošković: Changes in the natural philosophy

**Mjesto i datum**

Cres, Hrvatska, 21-24.09.2011

**Vrsta sudjelovanja**

Predavanje

**Vrsta recenzije**

Domaća recenzija

**Ključne riječi**

Ruđer Bošković; Orazio Borgondio; Isaac Newton; Jean-Jacques Dortous Mairan; Giovanni Poleni; Christian Mayer; Earth’s atmosphere; polar light / aurora borealis

**Sažetak**

Between his studies of philosophy and theology, Ruđer Bošković worked for six years as a magister in the lower classes of the two Jesuit colleges: in Rome and in Fermo, but in addition to his regular teaching duties, from 1736 he embarked upon the research and publishing of the treatises in mathematics, astronomy and meteorology. The fruit of such scientific interest is the treatise De aurora boreali, which Bošković submitted to the academic public on two occasions, first in August 1738 at the Roman Seminary (in Seminario Romano), and at the Roman College (in Collegio Romano) the following month, shortly before he began his studies of theology. Based on Martinović’s translation of the treatise De aurora boreali into Croatian, it is interpreted and commented from the perspective of the history of science (Martinović) and from the standpoint of the physics of the atmosphere (Vujnović and Lisac). In constructing the treatise, young Bošković followed the scientific style of his professor of mathematics Orazio Borgondio, who at the Collegium Romanum published treatises with the same text organisation from 1713 to 1734: division into propositions and corollaries. By that time Bošković zealously read Newton’s Opticks, the latter’s first Latin edition from 1706, for in the treatise he cited Query 20, where Newton concludes that “the density of air is proportional to the force compressing it”. He rightly leaned on Mairan’s famous treatise Traité physique et historique de l’Aurore Boréale, first published in 1731 in the Mémoires de l’Académie Royale des Sciences in Paris, and two years later in a separate book. Bošković used the method that Mairan applied for the calculation of the aurora height which appeared on 19 October 1726, and borrowed also two of his drawings, adapting them to his conclusions and calculations. For the appearance of aurora borealis on 16 December 1737, he drew on the report Observatio Aurorae Borealis, visae nocte insequenti diem XVI. Decembris, Anno 1737 by Giovanni Poleni, professor of mathematics at the University of Padua, published in Venice in 1738 together with four other reports. Bošković’s third valuable source for the topic of aurora borealis was the Moravian astronomer Christian Mayer, because the Ragusan in his treatise also applied Mayer’s method for the determination of the aurora height from a single position. Lastly, young Bošković shaped a scientific instruction “what to observe in these phenomena in future”. (IM) Four of the five propositions of Bošković’s dissertation deserve scientific commentary. In the second proposition Bošković depicts a method for the calaculation of the height of Earth’s atmosphere: taking that first solar rays are seen when the Sun is 18º under the horizon, he constructs the path of light, which, with two “reflections”, leads to atmospheric height of 20 km. Although Bošković’s result is acceptable in comparison with the contemporary measured results, it is rather the fruit of pure chance than of the sound model, since the passage of light through the atmosphere is much more complex than in Bošković’s model. The third proposition contains the main task of Bošković’s dissertation: determination of the aurora height. Based on the data collected by observing the phenomenon in Rome and in Paris on 19 October 1726, and with the help of planimetry and planar trigonometry, Bošković calculated the aurora height as being 1080 km. The fourth proposition solves the same problem of the aurora as observed on 16 December 1738. This time Bošković evaluated its height as being 1220 km. The present results show that polar light appears in the atmospheric layer between 100 and 1000 km. Therefore Bošković’s result can be understood as a slightly exceeded value of the upper limit of the phenomenon. Inaccurate determination of the height for several hundreds of kilometers was obviously possible due to complex structure of the phenomenon. One should bear in mind that the regular geometrical shape of the polar light is actually a crude approximation. By using Mayer’s method, Bošković solved the theoretical problem in the fifth proposition: how to determine the height of auroral oval which is centred on the geographical pole and whose plane is orthogonal to the Earth’s rotation axis. In the sixth, last proposition of his dissertation Bošković adhered to Mairan’s explanation of the physical cause of polar light: Solar rotation, documented by the motion of solar spots, can lead to deformation of the solar atmosphere, which therefore obtains convex shape and is extended to ecliptic and flows into Earth’s atmosphere. By analysis and commentary of the conditions under which rarefied solar atmosphere mixes with the high rarefied layer of Earth’s atmosphere, Bošković elaborated Mairan’s hypothesis and supplemented it by a conclusion acceptable for contemporary explanation of the generation of the phenomenon. (VV, IL)

**Izvorni jezik**

Engleski

**Znanstvena područja**

Fizika

**POVEZANOST RADA**

**Projekt / tema**

191-1911112-1092 - Boškovićeva Theoria philosophiae naturalis i hrvatske filozofske tradicije (Ivica Martinović, )

**Ustanove**

Prirodoslovno-matematički fakultet, Zagreb,

Institut za filozofiju, Zagreb

**Autor s matičnim brojem:**

Vladis Vujnović, (53655)

Inga Lisac, (26034)

Ivica Martinović, (157212)