Prof. De Morgan on the earliest Trigonometrical Canon, 517 



white shining plates. It contains neither cyanic acid nor 

 aniline. It may be heated with hydrochloric acid or potash 

 without decomposition. It is a kind of urea, in which the am- 

 monia is replaced by aniline. I was in hopes that this body 

 would possess basic properties, and like urea form crystalline 

 salts with nitric and oxalic acid ; its properties are however 

 totally different. 



I shall in a separate memoir return more fully to this pro- 

 duct of the decomposition of aniline. 



LXXIII. On the almost total Disappearance of the earliest 

 Trigonometrical Canon. By A. De Morgan, Esq."^ 



I LATELY found in a second-hand book-shop a trigono- 

 metrical canon, by the celebrated Rheticus, which was 

 totally new to me, and, as I afterwards found, would have been 

 just as new to any of the historians of astronomy and mathe- 

 matics. I am therefore induced to make a communication on 

 the subject to the Astronomical Society, which, more than any 

 other, has a right to take interest in the history of tables for 

 the facilitation of the appUcation of arithmetic to geometry. 



The paper which I now read is a remote consequence of 

 the proscription of Copernican opinions by the Inquisition. 

 No follower of Copernicus was more zealous or more plain- 

 spoken than Rheticus or George Joachim of Rhaetia. The 

 master, whether from conviction or policy, called his theory 

 no more than an hypothesis for the explanation of the pla- 

 netary motions : the pupil strongly insisted on the absolute 

 physical truth of the motion of the earth. Both were gathered 

 to their fathers long before the storm arose : but long before 

 that time arrived there was a distinction drawn between the 

 treatment of the two. In the Index Expurgatorius, it is not 

 Copernicus who is forbidden to be read generally ; the pro- 

 hibition only extends to the work De Revolutionibus^ and is 

 accompanied with a nisi corrigatur. But Rheticus is wholly 

 forbidden to be read in any of his works : nay, in Sotomaier's 

 folio edition of the Index (Madrid, 1667), even the Opus Pa- 

 latinumf though all but the very table is the work of Valen- 

 tine Otho, is an unlawful book, unless on the condition that 

 the praises of Rheticus in the preface be erased or passed over. 

 And Riccioli tells us that the condemnation of the books of 

 Rheticus took place in 1550, which is the year before the ca- 

 non I intend to describe was published. The extreme severity 

 with which his writings were treated will appear less remark- 

 * From the Monthly Notices of the Royal Astronomical Society, vol. vi. 

 p. 221 (having been read before the Society April 11, 1845); with aa 

 addition by the Author. 



