134 



♦ KNOWLEDGE ♦ 



[Feb. 13, 1885. 



goientific world to rights, men with chemical theories that 

 f.ocount for everything, Regenerators of Society by the 

 simple process of plundering the rich to bi ing them to the 

 level of the poor, propounders of bran-new hypotheses on 

 the nature and relations of Mind and Matter, Tiisectors of 

 Angles by Euclidean geometry, itc. Also readers anxious 

 to teach me how to edit. Examinees who want equations 

 solved, or sentences construed for tliem ; beginners who have 

 made a snulT-bjx from directions given in (say) the rarlour 

 Calhietmak'r, and wish me to tell them why the hinges 

 don't work ? — and so on. And woe to me if I even venture 

 to point out the fallacy of any of their assumptions to 

 these genti-y, or to hint that I am not a " crammer," or 

 private tutor or the like, or in fact that I know my own 

 business ; the next week's post brings nie sheets of abuse, 

 which of course go into the was- tepapc-r basket straightway. 

 Another horrible nuisance is the man who will send 

 an exposition of his theory (showing, we will suppose, that 

 the pole star is very much nearer to the earth than the sun 

 is), and requestir-g the Editor to write to him privately and 

 disprove it ! What idea tiich a ] erson can have of the 

 functions of an Editor or of the time at his disposal, it 

 would be ditEcult or impossible to cnnceive : a remark 

 which will equally apply to the writers of letters wanting 

 me to sell to or buy from them numbers of this magazine. 

 Having thus raised the curtain a vtry little way, I may 

 perhaps express a hope that the next time the reader comes 

 across an answer which he may feel tempted to regard as 

 snappish, he will reflect that it has probably been written 

 under circumstances of very strong jirovocation indeed. 



IxfbifUiSf* 



Now, here is an example which has just reached me. 

 The gentleman who favours nie with it, I\Ir. J. Murray, is 

 either the author, dpf'Stle, or jirophft of ■«hat he calls 

 "the P. D. theory.^' Whether "P. D." stands for Pure 

 Delusion, Perfect Drivel — or what, I have not the most 

 distant idea. 



Editor 



Dear, Sir ; Feb 2end 1865 



I cannot make out what the master wants to be at. In the 

 last three years, he has torn up all the Theorys on astronomy both 

 old and new, as he expounded them aijd showed the defect, he cast 

 them all on one side, even his own has gone to the wall. I am 

 pleased to think he has not giving up the P. D. system all together, 

 as it is capable of showing how the planets form those tictitions 

 loops or lines of demarcation, as they roll round there orbits with- 

 out rolling a round the sun. Also, I am pleased to hear my 

 Master speak of the Sun, having an influence over the contraction 

 or over the contracted matter that envelop our earlh: This is all 

 the Sun can do, to expand that which is contracted, just the same 

 as the light of our earth makes the moon form such a par.icentric 

 orbit or showes that our earth's light or influence over the moon 

 must be as strong as the Sun's influence over the Moon. If the 

 moon has no atmosphere how will you get the Sun's expansion to 

 act upon the contraction if there be none, if the moon has little 

 atmosphere it may be highly contracted, therefore, expansion can 

 play a higher part, especially if there is no angles to here the moon 

 on its way. The P. D. system can show all the eccentric motions, 

 tliat appears in the Heavens. Yours truely, J JIvkrat. 



I wonder whether " the P. D. system " can show all the 

 •eccentric motions that appear in the eaith (say, for 

 •example, in the shape of letter-writing) as well ! 



Me. W. August. Carter, of South Norwood, writes us:— I have 

 lately made an analysis of the digestive organs of the Grey Mullet, 

 which species of fish differs in this respect from all its congeners, 

 it being partial to no food that has life. I find that it possesses 

 a gizzard identical with that of a fowl, instead of the ordinary 

 organic structure, which I believe is a unique feature amongst 

 lishes. This peculiarity, however, is concurrent with the station 

 of existence which it is preordained to occupy, and in accord with 

 •the nature of its food, which consists of soft, fat substances, such as 

 4ecomposed refuse and vegetable matter. 



SOME BOOKS OX OUR TABLE. 



A History of Greek ifathernatics. By J. Gow, M.A. 

 (London : C. J. Clay it Son. 1884.) — Not a very attrac- 

 tive title truly, nor one giving promise of anything but the 

 dryest reading ; and yet it prefaces a book of the most 

 curious interest, and an excellent example of scholarly 

 research. The first portion of the work deals with the 

 Aryan numerals and the origin of the Decimal scale ; as 

 also with Egyptian arithmetic, as having contributed to the 

 subsequent development of that of Greece. In Part II. 

 the history of Grtek Aii hmetic is dealt with in detail, and 

 we learn under what disadvantages the Hellenic calculator 

 laboured ; one of the most potent being his imperfect form 

 of notation. The progress of the theory of numbers is 

 tlien described, and here the student will find a kind of 

 precis of the arithmetical books of Euclid's " Elements," 

 now wholly disused. In the succeeding chapters pre- 

 hi.>toric geometi y is traced to the expression of the relations 

 between parts of space in terms of fixed units of length, 

 area, and solidity ; and as Greek geocuetry possibly, and 

 even probably, may have had its oi igin in Egypt, a short 

 account of wliat has come down to us of Egyptian geometry 

 is given. The remainder of Mr. Gow's volume traces the 

 history of the geometry of Greece from Thales down to 

 Pappus, and very strange and interf sting it is to note the rude 

 inception of ideas familiar enough to the mathematician of 

 to day, and the increase of compactness and elegance in the 

 methods of proof. Ihi?, in fine, is a work which supplies 

 a real want in English literature, and which it is not much 

 to the credit of (ur nation that we shou'd have so long 

 been without. It is only fair to say that it was worth 

 waiting for. 



An Elementary Treatise on Dynamics. By Benj. 

 Wjlliamsox, M.A., F.R S , and Fran. A. Tarletox, LL.D. 

 (London : Longmans, Green, i Co. 1885.) — The authors 

 modestly stjle this "an Eitmentary Treatise;" and so, as 

 regards its preliminary ]/ortion, it undoubtedly is. The 

 student, however, who will master the contents of the 

 volume before us, will find that he has obtained a gi-asp of 

 Kinematics, Kinetics, and the theory of Thermodynamics, 

 which, for all ordinary purposes, will leave him but little 

 necessary to acquire. The modern doctrine of energy is 

 admiiably explained, and the numerous very practical 

 examples scattered through the text as admirably illustrate 

 the exposition of (he theoretical principles ta which they 

 are appended. With so much to admire, we are unwilling 

 to make (what may appear) any merely carping criticism ; 

 but we wish that our authors had avoided the use of the 

 expression "Centrifugal Force" in the second section of 

 their fifth chapter. 



Photo - Micrography. By A. Cowley ^Mallet, B.A , 

 M.B., itc. Second Edition. (London : H. K. Lewis. 

 1885 ) — The practical microscopiist is familiar with the 

 difliculty often experienced (very notably with high powers) 

 in re-detecting details of structure perceived under excep- 

 tionally advantagous circumstances ; and of the paramount 

 importance of preserving some delineation of what he has 

 seen. Many observers are sufficiently expert in sketching, 

 with the camera lucida, the neutral tint plate, or SOmmering's 

 steel disc ; but, unfortunately, their witness does not always 

 agree together, and two draughtsmen will rot unfrequently 

 give very difi'erent sketches indeed of the Fame object. Of 

 course, in one sense, photography furnishes an unerring 

 record of what the instrument reveals, and it is to teach the 

 worker with the microscope how to photograph his objects 



