28 



ON THE PERIODICITY OF THE AURORA BOREALIS. 



Sept. 5. Mairan and Pilgram. 



" 6. Celsius, Mairan, and Pilgram. 



" 7. Celsius and Mairan. 



" 10. Mairan and Pilgram, 



" 12. Mairan. 



" 16. Lynn. Folkes. 1 Frobes, Mairan, and Pilgram. 



" 17. Berlin. Kirch. Frobes and Mairan. 



" 18. Berlin. Kirch. Frobes and Mairan. 



" 22. Mairan and Short. 



Oct. 3. Berlin. Kirch. 



" 3. Celsius, Mairan, and Pilgram. 



" 7. Berlin. Kirch, Mairan. 



" 8. Celsius and Mairan. 



" 9. Celsius and Mairan. 



" 10. Celsius and Mairan. 



" 14. Lynn. Folkes. Celsius. 



" 14. Frobes, Mairan, and Pilgram. 



" 15. Celsius, Mairan, Pilgram, and Phil. Trans. 



" 19. Frobes and Mairan. 



" 20. Frobes and Mairan. 



" 21. Frobes and Mairan. 



" 25. Frobes and Mairan. 



" 26. Frobes and Mairan. 



Nov. 3. Celsius and Mairan. 



" 9. Mairan and Pilgram. 



" 10. Upsal. Burman. 2 



" 10. Celsius, Frobes, and Mairan. 



" 1 4. Frobes and Mairan. 



" 22. Frobes and Mairan. 



" 23. Frobes and Mairan. 



" 24. Frobes and Mairan. 



Dec. 3. Frobes and Mairan. 



" 4. Celsius and Mairan. 



" 12. Frobes and Mairan. 



" 15. Frobes and Mairan. 



" 31. Ltaly? Manfredi. Frobes and Mairan. 



1723. 



Jan. 1. Lynn. Folkes. Celsius and Mairan. 



" 3. Paris. Mairan. Celsius and Pilgram. 



" 6. Frobes and Mairan. 



" 12. Frobes and Mairan. 



" 14. Frobes and Mairan. 



i Phil. Trans., XXXII. 



2 Acta Lit. Succia, I. 393. 



3 Mairan says (p. 208) it was the first observed in that country. 

 Comm. Acad. Bonon., I. p. 297. This corrects the statement of 

 Musschenbroek, quoted in my former Memoir. Mem. Amer. 

 Acad., IX. 103. The aurora of March 17, 1727, was the first 

 observed by an astronomer. 



1724. 

 Jan. 17. Celsius, Frobes, and Mairan. 

 " 22-3. Upsal. Burman. 2 

 " 29. Celsius, Frobes, and Mairan. 



i Phil. Trans., XXXIV. 255. 

 2 Acta Lit. Suecia;, II. 13. 



