Nov. 17, 1882.] 



• KNOWLEDGE ♦ 



409 



mixture of the two sorts. — 0. W. P. Pardon me ; I hare not put 

 the growth of the oak from the acorn as a proof of the doctrine of 

 evolution. Both are illustrations of the wonderful operation of 

 those laws which the Creator has assigned to his works. You say 

 the acorn is the product of a perfect form. How do yon know- 

 that 'i By the result Only ; for no man can recognise a perfect 

 oak in aii acorn. In like manner I find the forms you speak 

 of as immature (though, by the way, the acorn is scarcely a 

 mature article) mii.^t be perfect, for they develop to perfect 

 forms.— G. N. Lt.-CuL. Sorry for the delay, but between 

 the comet and the transit astronomical matters rather crowd 

 us. — A. F. (). Two comets travelling along precisely the same 

 orbit near ;the sun would, of course, pursue also the same 

 orbit far from him. But an orbit of great eccentricity, and witb 

 perihelion very near the sun, would be changed to one appreciahhj 

 the same near the sun, but very different at a distance from him. 

 3Ir. Nelson's remark must have been misunderstood by the Athenwum 

 ivriter. It is perfectly correct, of course, but my friend Mr. 

 Neison is not in the habit of announcing that two and two make 

 four.— Jos. Clakc. See letter about Rainband Spectroscope in 

 No. 53. — H. W. C. K. (1.) See advertisements as to star maps for 

 November and December. (2.) There is no mistake, either of 

 engraver's or of mine. The signs of the zodiac were all right in 

 their proper constellations two thousand years ago, at about which 

 time, having for two thousand previous years been travelling 

 athwart their constellations, they began to leave them. The 

 cause was and is the precession of the equinoxes. (3.) That 

 method of copying drawings is not suitable for drawings on thick 

 paper. — Dens. " I think I can answer that tooth question myself, 

 for, sixteen years ago, I consulted a dentist about just such tiny 

 black marks on a tooth. He scraped them out a little, and filled 

 ■with gold, and I have had no more trouble with them. It is rather 

 strange, by the way, that all the trouble I have ever had with 

 my teeth began and ended (so far, I mean, as actual mischief 

 ■was concerned) when I was at Cambridge, whence you -write. — 

 P. D. Glad of your kindly words. (I.) It would be difficult to say 

 which pictures in ordinary galleries are " improper." There are 

 paintings from which some turn away as if they were ashamed to 

 look at them which are full of grace and beauty, and perfectly 

 ■wholesome to healthy minds. I agree with you if you mean the 

 coarse pictures'of Bacchanals (hideous beasts !) by N. Ponssin, and 

 the like. (2.) Yes, " ' allegiance,' ' loyalty,' and ' faith,' have 

 been most nobly exhibited as between man and man, not between 

 corporations, boards, and societies." Allegiance to the state, as 

 the highest form of patriotism, is a worthy quality all the same. 

 But if one sees a Fijian (for example) devotedly loyal (save the 

 mark) to his chief, because that person is descended from X., a 

 pirate warrior of some other race, and from Y., another pirate 

 chief of yet another race (who perhaps conquered X.'s descendants, 

 but married with a female representative), each descent being 

 traceable through twenty generations along a line including nine or 

 ten murderers, ten or twelve imbeciles, a few bastards, and some 

 casual lunatics by intermarriages -with neighbotiring Polynesian 

 races of more savage origin still, then science recognises a most 

 interesting problem in tracing the growth and development of this 

 most preposterous Fijian superstition. Yet a Fijian of twenty 

 generations back, fighting for his chief and cheerfully giving up 

 his life to save that of the leader of his people, showed true 

 loyalty, and deserved to be held in loving remembrance by all his 

 tribe — so greatly do circumstances alter cases. — K. H. A. Those 

 lottery schemes are as honest as such schemes can be ; that is, 

 they are quite rascally. You know your chances and take them, 

 and the company pockets assured profits, having not benefited but 

 injured their kind. — H. Ccmberg. The effect of repeated doublings 

 is indeed great ; but I think it is pretty well known. — R. Waugh. 

 My lecture has not been published. — Alfd. Dbay. Better observe 

 when the pole-star is just above or just below the pole ; or else 

 just to right or left, correcting for the star's distance from the 

 pole. In my " Easy Star Lessons " the times when the pole-star 

 is in these positions are given. — W. J. Palethobpe. Do not know 

 the weight of the large mirror of the Rosse telescope, or of the 

 Princeton lens. The diameter of the groat mirror of the former 

 instrument is 8 feet. — M. C. S., will be obliged to any correspondent 

 giving information respecting the so-called caterpillar-tree of New 

 Zealand. Wo have seen it, and been told much about it ; but our 

 informant w^as not scientific. — K. S. Purcell. Thanks.— Enitok 

 UT ViNCAM, H. W. L. (?), A. A., Grisel. I believe you can always 

 get Hamiltonian translations of Latin works at secondhand book- 

 stalls. They explain themselves. You read on till you find 

 yourself falling into the swing of the hinguage and catching its 

 idioms— it is just as if you heard the language spoken, and were told 

 its meaning — just, in fact, as you pick up a foreign language when 

 you live among those who speak it. Then you begin to combine 

 this process with the study of the grammar — such simple books as 



Arnold has ■written, not the ridiculous books devised to perplex 

 unhappy beginners. You gradually extend your vocabulary ; but 

 by reading, not by wearing out dictionaries. You will be told that 

 this easy way of learning is not so good for you as the old-fashioned 

 way, which reverses the usual order, and sets you learning rules 

 before you know what they are about. It is not what .-i 

 boy is told, said a learned idiot, but what he teaches him- 

 self, that is of use to him ; whcreimto the Kev. Sydncx- 

 Smith rightly made answer, that one might as well ray it i- 

 not the clothes a boy puts on that covers his nakedness, but 

 those he makes for himself. I can only say, that having occasion 

 thirteen years ago to review a German book, and knowing practi- 

 cally nothing of German, I bought four or five Hamiltonian books 

 of German in Holywell-street, reviewed that work in less than a 

 fortnight, after reading and enjoying it (the review appeared in 

 Nature, and was republished in my " Light Science for Leisure 

 Hours,") and that ever since I have been able to read any German 

 prose I have yet come across, with such occasional aid from a 

 dictionary as is rendered necessary by defects in my German 

 vocabulary. A German grammar I found exceedingly interesting 

 after I had thus got the swing of the language. — F. Chapman. If 

 ii! = number of bullocks, i/ = number of sheep, and = = number of 

 pigs, you have (using the half-sovereign as coin unit) 

 20x-i-6!/-n = 200 

 x + y + : = 100. 

 whence 19 a; -H 5 t/ = 100, an indeterminate equation as it stands, 

 but determinate if combined ■with the condition that x and y are 

 both positive whole numbers, neither being zero. For it is obvious 

 that X must be a mijtiple of 5, and cannot be a greater multiple 

 than 5 itself, for if x were 10, y would be negative. Therefore, 

 x = 5, whence y = l, and a; = 94; making the total price paid 

 for the bullocks £50 ; for the sheep, £3 ; and for the pigs, £47. 



ELECTRICAL. 



H'sETT. — Very ingenious. Terrestrial magnetism is to all 

 appearance the result of electric currents. Magnetism can scarcely 

 be substituted for gravitation, because — if for no other reason — 

 gravitation is an attractive force, exerted by all forms of matter 

 in proportion to the bulk, bnt irrespective of chemical or physical 

 constitution. — A. W. L. The slope is of no importance, and is 

 only made for the sake of appearance, etc. — G. McIntosh. 1. Anent 

 lead filings, try the experiment and see how it answers, but lead 

 is the ultimate condition of the peroxide. Might not the hea^vj- 

 filings tear the spongy lead away ? 2. Better use felt or asbestos, 

 not cardboard. 3. Quantity and intensity are terms which have 

 served a good purpose, but are now dying out. The fourth article on 

 " Measurement " should help you to understand them, bnt another 

 article is to follow, which, as it may remove your difficulty, please 

 see. 4. The intensity or E.M.F. of secondary batteries is depen- 

 dent on their constituents and independent of the charging 

 current. A ctirrent of low E.M.F. may be transformed 

 into one of high E.M.F. by charging the accumulators in 

 parallel circuit or quantity, and discharging them in series. 5. 

 You were right in connections, as the discharging current is oppo- 

 site in direction to the charging current. 6. 'The E.M.F. of a 

 dynamo varies as the number of revolutions niade by the armature, 

 and the intensity of the magnetic field affects the amount or 

 strength of the current. 7. Don't quite see what you mean. 8. A 

 motor, generally speaking, requires a current of low E.M.F. The 

 little Griscom takes 12 volts. 9. I should not, under any circum- 

 stances, recommend Bennett's battery. Its E.M.F. is 1'5 to 1'8. 

 It polarises like the Leclanche, and the recovery is slower than in 

 that battery. Try Higgin's Bichromate battery.— H. W. U. Use 

 white wax instead of the varnish. — Errol (?). Let me know the 

 resistance of your battery. — R. O. Tho sounds may have resulted 

 from indifferent insulation, considering the relatively high E.M.F., 

 the "cracking" probably being caused by the passage of minute 

 sparks between the wire and the frame of the instrument. The 

 variations of tho current were evidently too rapid to affect the 

 galvanometer. 



JJlfT Drydn. 

 *• Three Pens for three essenti&l virtues famed, 

 The Pickwick, Owl, and Wavtrley were named, 

 Tho first in fleiibility sun'Msed, 

 In ease the next, in eleeanee the last. 

 These jioints united with attractions new, 

 Have jielded other boons, the Phaeton aaiHin'too." 



Sample Boi, with all the kinds, Is. Id. by Post. 



** Let those write now who never xrrote before ; 



And those who always wrote now write the more." — Ohan Timet. 



Pnlrnlert of Pent and Pmholdert. 



M.\CNIYEX & CAMERON, 33. Blair-stbbbt, KnynmoB. 



Fehuakebs to dss Muistt's Govbbxubrt Orricia. (Est. 1770.) 



