522 Prof. De Morgan on the almost total Disappearance 



not find any date to the reprint, nor do 1 know from whence 

 Miirhard and Lalande got theirs. The copy of the original 

 edition now in my possession probably escaped the Inquisition, 

 from the accident of its being bound up with the cditio prin- 

 ceps of the Greek text of the optical writings of Euclid, pub- 

 lished six years after it. 



We thus see that the existence of a work may be forgotten, 

 and the fair claims of its author reduced in amount, by the 

 neglect of a biographer in stating precisely its title, date, place, 

 and form ; and also that it may be possible, partially at least, 

 to repair the neglect, by collection of scattered notices. We 

 also see that the publication of proper catalogues of our libra- 

 ries would tend to promote historical knowledge. And while 

 on this subject, I trust it is not out of place to make the fol- 

 lowing remark. I very much fear that the publication of a 

 good alphabetical catalogue of the splendid library in the Bri- 

 tish Museum is retarded, by the demand which has often been 

 made for a classed catalogue, or one arranged in order of sub- 

 jects. From much, almost daily, use of catalogues for many 

 years, I am perfectly satisfied that a classed catalogue is more 

 difficult to use than to make. It is one man's theory of the 

 subdivision of knowledge, and the chances are against its 

 suiting any other man. Even if all doubtful works were en- 

 tered under several different heads, the frontier of the dubious 

 region would itself be a mere matter of doubt. I never turn 

 from a classed catalogue to an alphabetical one without a feel- 

 ing of relief and security. With the latter I can always, by 

 taking proper pains, make a library yield its utmost : with the 

 former I can never be satisfied that I have taken proper pains, 

 until I have made it, in fact, as many different catalogues as 

 there are different headings, with separate trouble for each. 

 Those to whom bibliographical research is familiar, know that 

 they have much more frequently to hunt an author than a 

 subject : they know also, that in searching for a subject, it is 

 never safe to take another person's view, however good, of the 

 limits of that subject, with reference to their own particular 

 purposes. 



I now proceed to the description of the canon. 



The title is " Canon doctrinse triangulorum. Nunc pri- 

 mum a Georgio Joachimo Rhetico, in lucem editus, cum pri- 

 vilegio imperiali, Ne quis hasc intra decennium, quacunq; 

 forma ac compositione, edere, neue sibi uendicare aut operibus 

 suis inserere ausit. Lipsiae ex officina Wolphgangi Gunteri. 

 Anno M.D.LI." quarto. The title is followed by one page of 

 verses, fourteen of tables, and six of dialogue. In the title- 

 page is an obelisk, with a man drawing a diagram on the base. 



