VOL. LI.] I'HILOSOPHICAL TRANSACTIONS. 421 



more particularly in the island of Ceylon, where it is called by the natives tour- 

 namal. 



The first account we have had, of late years at least, of this extraordinary 

 stone, was in the History of the Royal Academy of Sciences of Paris, for the 

 year 1717; where we are told, that Mr. Lemery exhibited a stone, which he 

 said was not common, and came from Ceylon. This stone attracted and repelled 

 little light bodies, such as ashes, filings of iron, bits of paper, and such like. 

 The publisher of that history then proceeds to give some reasons for these phe- 

 nomena. Linneus, in his preface to the Flora Zeylanica, mentions this stone 

 under the name of lapis electricus; and takes notice of Lemery's experiments 

 before-mentioned. Notwithstanding this, no further mention was made of this 

 stone, and its eflfects, till very lately. The Duke de Noya, in his letter to M. 

 de Buffon, informs us, that when at Naples in the year 1743, the late Count 

 Pichetti, secretary to the king, assured him, that during his stay at Constanti- 

 nople, he had seen a small stone, called a tourmaline, which attracted and re- 

 pelled ashes. This account the Duke de Noya had quite forgot; but, being last 

 year in Holland, he saw and purchased two of these stones, which are there 

 called aschentrikker. The making experiments with these called to his remem- 

 brance what formerly had been told him by Count Pichetti. With these stones 

 he made, in company with Messrs. Daubenton and Adanson, a great number 

 of experiments, of which the duke has favoured the public with a particular 

 account. 



In the year 1757, there were two accounts published on this subject: the one 

 is a memoir of M. ^pinus, read to the Royal Academy at Berlin, intitled, De 

 Quibusdam Experimentis Electricis Notabilioribus. The other is a treatise in 

 quarto, printed at Rostock, intitled, Disputatio de Electricitatibus Contrariis. 

 Auctore Joanne Carolo Wilke. Since which time. Dr. Heberden, having pro- 

 cured some of these stones from Holland, a great number and variety of expe- 

 riments with them have been made here, particularly by Mr. Wilson ; an account 

 of which he has very lately communicated to the Royal Society. 



XXXVUI. An /Jttem.pt to Account for the Regular Diurnal Variation of the 

 Horizontal Magnetic Needle ; and also for its Irregular Variation at the 

 Time of an Aurora Borealis, By John Canton, M. A., F. R. S. p. SQS. 



The late Mr. George Graham made many observations on the diurnal varia- 

 tion of the magnetic needle, in the years 1722 and 1723 : but declared himself 

 ignorant of the cause of that variation, in N° 383 of the Philosophical Trans, 

 actions, where many of those observations are to be found. About the year 

 1750, Mr. Wargentin, secretary of the Royal Academy of Sciences in Sweden, 

 took notice both of the regular diurnal variation of the needle, and also of its 



