DISCOVERIES IN THE CELESTIAL SPACES. 337 



ined empirically the position of the magnetic south pole ; aud 

 since my honored friend, the great mathematician, Frederic 

 Gauss, has succeeded in establishing the first general theory 

 of terrestrial magnetism, we need not renounce the hope that 

 the many requirements of science and navigation will lead to 

 the realization of the plan I have already proposed. May 

 the year 1850 be marked as the first normal epoch in which 

 the materials for a magnetic chart shall be collected ; and 

 may permanent scientific institutions (academies) impose upon 

 themselves the practice of reminding, every twenty-five or 

 thirty years, governments favorable to the advance of naviga- 

 tion, of the importance of an undertaking whose great cosmic- 

 al importance depends on its long-continued repetition. 



The invention of instruments for measuring temperature 

 (Galileo's thermoscopes of 1593 and 1602,* depending simul- 

 taneously on the changes in the temperature and the external 

 pressure of the atmosphere) gave origin to the idea of determ- 

 ining the modifications of the atmosphere by a series of con- 

 nected and successive observations. We learn from the D> 

 ario dell' Accademia del Cimento,' 'which exercised so happy 

 au influence on the taste for experiments, conducted in a reg- 

 ular and systematic method during the brief term of its activity, 

 that observations of the temperature were made with spirit 

 thermometers similar to our own at a great number of sta- 

 tions, among others at Florence, in the Convent Degli Angeli, 

 in the plains of Lombardy, on the mountains near Pistoja, and 

 even in the elevated plain of Innspruck, as early as 1641, an 

 five times daily .t The Grand-duke Ferdinand II. employed 

 the monks in many of the monasteries of his states to perform 

 this task.J The temperature of mineral springs was also de- 

 termined at that period, and thus gave occasion to many ques- 



* On the oldest thermometers, see Nelli, Vita e Commercio Letter aria 

 di Galilei (Losanna, 1793). vol. i., p. 68-94 ; Opere di Galilei (Pudovo, 

 1744), t. i., p. lv. ; Libri, Histoire des Sciences Mathema/iques en Italie, 

 t. iv. (1841), p. 185-197. As evidences of first comparative observa- 

 tions on temperature, we may instance the letters of Gianfrancesco Sa- 

 gredo ;md Benedetto Castelli in 1613, 1615, and 1633. given in Venturi, 

 Memorie e Lettere inedite di Galilei, Part i., 1818, p. 20. 



t Vincenzio Antiuori, in the Saggi di Naturali Esperienze, fatte nelV 

 Accademia del Cimento, 1841, p. 30-44. 



X On the determination of the thermometric scale of the Accademia 

 del Cimento, and on the meteorological observations continued for six- 

 teen years by a pupil of Galileo, Father Raineri, see Libri, in the An- 

 nales de C'himieet de Physique, t. xlv., 1830, p. 354 ; and a more recent 

 similar work by Schouvv, in his Tableau du Climat et de la Visitation 

 de. V Italie, 1839, p. 99-106. 



Vol. II P 



