520 Prof. De Morgan on the almost total Disajjpearance 



the latter, expresses a great desire to see a certain little book 

 of Rheticus, the title of which he does not mention. In a 

 subsequent letter of 1595, he reports that he has seen this 

 book, that it treats only of plane triangles, and that it strives 

 at {nititur) the canon of triangles which Rheticus afterwards 

 (olini) published. What can this canon of triangles hel At 

 the date of this last letter, the Opus Palatinum was not pub- 

 lished. It can refer to nothing but the work which I now 

 bring forward, and which, it thus appears, was known. The 

 next witness I shall cite is Thomas Digges, who is likely to 

 have taken a particular interest in the writings of his fellow 

 Copernican. In the Ala; seu Scalce Mathematics, published 

 in 1573, during the life of Rheticus, Digges says that those 

 who dislike labour should consult the tables of the proportions 

 of right-angled triangles by Rheticus, of which tables he fur- 

 ther states that they go to every ten minutes. 



Valentine Otho, in the preface to the Opus Palatinum^ says 

 that " when Rheticus gave to the public a specimen of his me- 

 thod of enriching the canon and doctrine of triangles, he ex- 

 cited a wonderful degree of hope and expectation about it in 

 the minds of the learned, especially when in the dialogue 

 which he prefixed to his ten-minute canon, he brought for- 

 ward extraoi'dinary and almost incredible things concerning 

 its use." I produce to the Society the ten-minute canon with 

 the dialogue, which however is not prefixed to the table, but 

 follows it. Otho afterwards mentions this dialogue again, 

 and says that on reading it he was so struck with the preten- 

 sions of its author that he sought out Rheticus in Hungary, 

 and commenced the acquaintance which led to his becoming 

 the editor of his friend's posthumous work. He further adds, 

 that at their first meeting, when he had just stated that he was 

 come to acquire knowledge on the properties of triangles, 

 Rheticus interrupted him with, " You are just as old as I was 

 when I went on the same errand to Copernicus." Thus it 

 appears that this canon was the indirect cause of the publica- 

 tion of the Opus Palatinum. 



But nevertheless, this work is not mentioned in the cata- 

 logues of Lipenius, Dechales, or Murhard ; it is not alluded 

 to either by Riccioli, Clavius, Gassendi, Weidler, Heilbron- 

 ner, Delambre, Montucla, Hutton, or Kastner. Delambre 

 distinctly says he never heard of any canon containing sines, 

 tangents and secants, previous to that of Vieta : though else- 

 where he describes the preceding passage from Otho by saying 

 that Rheticus had published a programme of the Opus Pala- 

 timim, and even an extract for every ten minutes. But he 

 then quotes the account of Lalande, to which I shall immedi- 



