488 



NATURE 



March 26, 1896 



remove a misapprehension under which, it seems to me, that he 

 was labouring, after perusing my report, with regard to the 

 limit to which I suggest volumetric sizing. He seems to think 

 I advocate that the grading of the sand, which has been 

 separated, as far as feasible, from the slimes (which are to be 

 subsequently classified separately in four Spitz-Kasten), should 

 be effected through very fine sieves — 6o-mesh screens, or under. 

 I quite agree that to attempt to do so would fail. Such, how- 

 ever, is not the meaning, or, I think, the construction which 

 can be placed on the context of my report. A glance at the 

 diagram illustrating the sequence of the methods of reduction, 

 clearly shows, I submit, that it is only the coarser sands issuing 

 from the bottom of the slime separator, that are subjected to 

 " volumetric sizing *' in a trommel, which classifies them into 

 three grades, the finest being through a 40-mesh sieve, which is, 

 I apprehend, practically, the most suitable grade for the 

 Frue-vanners to do close work ; the overflow from the con- 

 centrates flowing into the Spitz-Kasten. 



I trust that these observations will dispel the misapprehension 

 which your correspondent entertained on this point at the time 

 when he wrote his article, as I respect his opinion, and would 

 regret to be misunderstood by him. Henry Rosai.es. 



I REGRET to have misunderstood Mr. Rosales, whose report 

 is certainly entitled to most respectful and careful consideration- 

 My mistake (a natural one, I think) arose from a statement 

 made on p. 13 of the report. Here Mr. Rosales says, in speaking 

 of the Johnson's Reef Gold Mines Company, Eaglehawk, that 

 "the battery sand should previously be classified into different 

 grades by ' sizing '. . . . Such could be accomplished by delivering 

 it into trommels fitted with screens of different meshes. The 

 mantel of the first trommel might be a sieve of 40 to 50 holes to 

 the lineal inch, and the second trommel might be covered with 

 a screen of 64 holes to the lineal inch. . . . This system of 

 sizing would certainly be applicable." (The italics are my own.) 

 On p. 50, where Mr. Rosales recurs to the subject of trommels, 

 he does not mention any screen finer than 40-mesh, but, on the 

 other hand, does not state that this is the finest that should be used, 

 and refers to it merely in the following words : — " Supposing it 

 {i.e. the trommel] to be covered with •j'.j or -^-^ wire gauze." Mr. 

 Resales' explanation will, I feel sure, be gladly received by 

 others, besides myself, who have read his valuable report. 



T. K. Rose. 



Crush-Conglomerates in Ireland. 



In your issue of March 5 there is a letter from Mr. McHenry, 

 in which he mentions the occurrence at Portraine and Lambay 

 Islands, Co. Dublin, of conglomerates which he considers to be 

 of the nature of crush-conglomerates. During the past two 

 summers we have been examining these sections, and can 

 corroborate Mr. McHenry's statements with regard to the 

 presence of crush-conglomerates ; but our investigations have not 

 led us to conclusions altogether similar to his, with regard to the 

 igneous rocks of the district. We hope to publish our results 

 before very long. S. H. Reynolds. 



C. I. Gardiner. 



CLAUDIUS PTOLEMY AND HIS WORKS. 



pLAUDIUS PTOLEMY I What reader of the most 

 ^—^ elementary science is not familiar with his name, 

 at least in adjectival form, in connection with the Ptolemaic 

 system, and yet how little is known of him as a personality. 

 That he lived in Egypt during the reigns of Hadrian and 

 Antoninus Pius, and made astronomical observations chiefly 

 on a terrace in Alexandria, sums up nearly the whole. 

 But his works (addressed to Syrus, of whom also nothing 

 is known) were the standards of authority in geography 

 and astronomy for many centuries after his death ; and 

 though the tide of science has left them far behind, they 

 can never be quite forgotten or cease to be of high in- 

 terest in scientific history. His great astronomical work 

 was translated into Arabic (changing its name in the 

 process), and on the revival of learning in Europe was 

 translated from that language into Latin, as it afterwards 

 was from the original Greek. A French version was 



NO. 1378, VOL. 53] 



published by Halma at Paris in 18 13- 16, but no English 

 rendering (except of small portions) has ever appeared. 

 The British Museum Catalogue shows that our national 

 collection contains a large number of Greek editions and 

 Latin translations of the Almagest (as the MadrjuariKTi 

 2vvTa^is is always called, from the Greek for "greatest," 

 with the Arabic definite article prefixed) and Geography 

 of Ptolemy, as well as of most of his smaller works ;, 

 Halma's editions of the Greek of the Almagest and Geo- 

 graphy, with French translation in parallel columns ; 

 and Italian translations of the latter and of the Optics. 

 Every student of Ptolemy must be under so much obliga- 

 tion to Halma, that it may be of interest to state that he 

 was born at Sedan in 1755, and after being Principal of 

 the college of his native town, became Professor of 

 Mathematics at the Prytande at Paris, where he held at 

 various times other offices, one of them being that of 

 librarian to the Empress Josephine. Besides his version 

 of Ptolemy and of the not very lucid Commentary of 

 Theon (father of the ill-fated Hypatia) on part of the 

 Almagest, he published a French translation of the 

 Phenomena of Aratus, and died in 1828. His edition of 

 the Almagest is preceded by an elaborate and interesting 

 preface, and has appended to it some Notes by Delambre. 

 Two of Ptolemy's minor works, the Planispha^rium and 

 the De Speculis, appear to be extant only in Latin 

 versions ; the chronological table, however, of reigns up 

 to his own time still exists in the original, whilst of the 

 astrological work called " Tetrabiblos " or "Quadripar- 

 titum," we have not only the Greek, but Latin, French, 

 and English translations. 



The Almagest was so exhaustively examined and com- 

 mented on by Delambre, that little can be added to his 

 conclusions.^ It is evident that Ptolemy's work is founded 

 chiefly upon the observations of Hipparchus, which were 

 made at Rhodes about three centuries before. Lord 

 Macaulay's omniscient schoolboy probably beheved that 

 Ptolemy founded the system by which sun, moon, planets, 

 and stars all moved round the earth, though the thought 

 may have crossed his mind that this view was held before 

 the appearance of the Alexandrian astronomer. This is, 

 in fact, somewhat akin to the extensively-believed idea 

 that Newton discovered the fact that external bodies are 

 drawn or attracted to the earth. What is really due to 

 Ptolemy as the author of the Ptolemaic system, is the 

 reducing into a systematic form for explaining the 

 planetary motions the ingenious imaginative machinery 

 of epicycles and deferents. This is now so generally 

 understood that we need not enlarge upon it here. It is 

 almost remarkable that his discussion of the motions of 

 the inferior planets, Mercury and Venus, did not 

 lead him to the elaboration of the Tychonic system, 

 something akin to which Vitruvius and Pliny seem to 

 have had in mind, and which would in that case have 

 held its ground for centuries ; when actually started by 

 the Danish astronomer, it was behind the age and soon 

 stranded by the advance of science, his own con- 

 temporaries seeing that its cause was hopeless from the 

 first. More credit is due to Ptolemy for his investigations 

 respecting the motions of the moon, which led him to the 

 discovery of the inequality known as the lunar evection. 

 The inequalities he endeavoured to explain by epicycles, 

 but for the latter he introduced in addition an eccentric, 

 the centre of which turned about the earth in a direction 

 contrary to that of the motion of the epicycle. A not in- 

 considerable portion of the Almagest is devoted to 

 eclipses and their prediction ; and we are indebted to 

 Ptolemy for an account of three eclipses of the moon 

 which were observed at Babylon in the years B.C. 721 

 and 720 under a king whom he called Mardokempados, 

 but whose real name was Merodach-Baladan, and who, 

 after a long contest, was completely crushed and de- 



1 A very able though shorter discussion is given in Narrien's " Historical 

 Account of the Origin and Progress of Astronomy." 



