so 



♦ KNOWLEDGE ♦ 



[Junk 30, 1882. 



'•lunbcki" — Persian tobacco. It is either very mild, or else the 

 process it undergoes, before reaching the lunprs of the smoker, robs 

 it v{ much of its strenj,nh. Before beini; placed in the nargileh it 

 is muist«Ded, and then the moisture squeezed forcibly from it. Let 

 Mr. Vrosser try to smoke the Knglish forms of tobacco — to wit, 

 shag, birdsoye, retnms, gold leaf, &c., Ac. — in a nargileli, and he 

 irill alter his opinion as to to the " tunbeki " of Constantinople j 

 but then he only took "one puff." Another case of noglcctod 

 opportunities! He missed the chance of making the ncquaintnnce 

 of a smoke which does not depress you, after which you liaTO no 

 desire to drink, and to which the lower class of Turks owo their 

 furiitude under difficulties, their suavity of manner, and temperance 

 in all things. ' A Co.\sT.tXT Keakeb. 



THE FEVER TREE. 

 U6]— Mr. Sonthall, writing of the Eucalyptus Globulus, seems 

 t think it has not yet been acclimatised in Europe. Perha])s I 

 may be allowed to say that it grows luxuriantly all along the 

 Biviera, and more particularly in the noighbom-liood of Cannes, and 

 if acclimatisation consists in bearing flowers and fruit in the open 

 air, it is certaiiJy there acclimatised, for 1 have seen there trees 

 from s.xty to one hundred feet high, perfectly loaded with the 

 bluish fruit, or more correctly seed-vessels, from which a pointed 

 capsule is thrown off by the magnificent crown of white stamens 

 and pistils which form the flower (there being, I believe, no 

 petals). The seeds contained in the hard, woody case, nro nume- 

 rous and extremely minute, much smaller than a grain of mustard 

 eeed, and it seems diOiculf to imagine a tree — such as ono I saw, a 

 perfect giant, growing in the gardens of the Duo de Vallambrosa, 

 ■wh.re it had been planted only in (I believe) 1865 — having sprung 

 from such a seed. 



The people of the south of France are greatly impressed with its 

 efficacy in fever and rheumatism, for which latter disease they wear 

 branches laid over the part affected, and you never mention the tree 

 to a ]>easant without hearing : " Ah, it is very good for the fever." 

 The manufacturers of Cannes use it largely in soaps and perfumes, 

 and one prejiaration, a toilet vinegar, is the most exquisitely per- 

 fumed and refreshing thing of the kind I have ever met with. It 

 seems a pity our chemists do not make more use of a tree which has 

 many capabilities, both as a febrifuge and a healthy and refreshing 

 perfume. A. W. Bickla.nd. 



GLASS STYLOGRAPHS. 

 [447]— WiU " H. L. C." (letter 424, p. 28, No. 32, Vol. II.) bo good 

 enough to enlighten your readers a} to the way ho makes hia glass- 

 tube pens (if not a trade secret) and oblige many others as well as 



ttis WllITEB. 



PROBABILITIES. 

 [418]— Tlie remarks of " N." (401) having passed without com- 

 ment, and fearing they may induce a belief in the advantage of a 

 syotem of increasing or decreasing stakes, I wish to contribute my 

 mite to dispel such an illusion in as few words as I possibly can. 

 If a die be thrown a finite number of times, and any ono stake his 

 money so as to gain a given sum per throw, and retrieve losses 

 on unsuccessful throws, provided the gamester's resources are un- 

 limited, it is evident that n trials ending with a successful throw will 

 yield n m (or m per trial), and this will happen whatever odds may 

 be laid ! But if the speculator is not possessed of unlimited rc- 

 eonrccB, there is no advantage in varying the stake in anyway. If a 

 single die Ije thrown ad infinitum, the number of times the die is 

 onsticcessfuliy thrown on the second trial in proportion to the 

 number of nntuccessful throws on the first trial, will bo as five 

 to six ; the numtx>r of unsuccessful throws on the third trial, 

 will bear the same proportion to the number of nnsuccessful 

 throws on the second trial, and so on. The number of times the 

 die is thrown successfully in proportion to the number of uusnc- 

 ccssfol throws on any trial will be always as ono to five, the 

 chance of throwing a die successfully always being the same, irre- 

 spective of how many times it rnny have been thrown successfully 

 or nnsnccesiifolly prerionsly. Any succession of successful or nn- 

 succcMful throws is no guide to what may follow, notwithstanding 

 the fact that the proportion of successful to nnsuccessful throws 

 will ultimately assume the proportion of one to five. When a die 

 is thrown a finite number of times, the greater the number of 

 throws, the nearerwill the result approach the theoretical numbers ; 

 for this reason, in throwing a die, the first time it is thrown suc- 

 cessfully, the die will only onco have Iwm thrown on that particular 

 trial, and that once sncccssfully ; if we continue to throw the die, 

 the ratio U.'t ween the successful and unsuccessful throws on that 

 particoUr trial will assume the proftortion of one to five, and the 

 one successful throw on one partictilar trial will be farther re- 



moved, and the more times the die is thrown, the farther removed 

 from the first trial will bo that trial in which each throw (one 

 or more) is successful. There is another increasing stake to 

 which the above remarks applj', viz., to win a given sum to- 

 gether with ))nst losses, so that if an ovont happen n times in 

 lit trials ending with a successful trial, you gain n times the sum 

 you sought to win on the first trial. This is exemplified by tossing 

 a i)enny, and doubling your stake each time you lose, reverting to 

 the original stake after each win. Supposing tho resources of the 

 gamester to be infinite, this is tho lowest rate of increment from 

 which any advantage can be gained. There would bo no advantage 

 in seeking to gain a given sum together with half tlie losses since 

 the last successful trial. In games of skill and clianco tho most 

 skilful player must ultimately win, as he is bonnd to get his share 

 of the luck, and it is to his advantage to increase the stakes at the 

 commencement of any fresh game, whether ho has been gaining or 

 losing previously. In playing any game of pure chance, there can 

 be no advantage from increasing tho stakes after a loss or a suc- 

 cession of losses ; if the odds are against you, you must lose ; the 

 higher the stakes, tho more you lose in proportion. Under any cir- 

 cumstances thero is no advantage in following any system of in- 

 creasing or decreasing stakes, or of investing so as to secure an 

 increasing amount of money either after a loss or after a gain. No 

 system has yet been or ever will bo devised that will convert 

 certain loss into certain gain. If you cinnot gain by making tho 

 stakes equal, you cannot by making them unequiil. 



Thomas Johson. 

 Bromley, Kent, June 15, 1882. 



SPECTACLES. 



[•1U>] — Suppose you give us an article u]iou spectacles when 

 convenient. A short time since I bought from a country dealer a 

 pair of suitable focus, 30 inches, and capital frame. They wore by 

 a celebrated maker, and marked by him as " pebbles." Their 

 nominal focus proved to be exact, each lens gave a neat solar image 

 at jjrecisely tho assigned distance, but on testing them between two 

 nicol ])risms, I found no change of light or colour, such as is ex- 

 pected from quartz in polarised liglit. 



Having a favourable opportunity, I submitted tho sjioctacles for 

 the several opinions of three practical opticians in Loudon. The 

 first said tho polish was apparently too perfect for glass i but 

 placing on a table before the window a pile of common window 

 glass, eight or ten pieces, perhaps, about C inches sqiniro — a polariz- 

 ing bundle in fact — he held a tourmaline before tho eye with one 

 hand, and a lens of tho spectacles in the other in the lino of sight 

 between the tourmaline and the plates, and at once pronounced tho 

 material to be glass and not quartz. The second roi'oroo jjroduced 

 a pair of tourmaline tongs, and placing a spectacle lens between 

 them, gave tho same verdict. Ho showed how, when tho tourma- 

 lines were "crossed," tho rotation of a "pebble" lens between 

 them restored the light at certain intervals ; whereas tho introduc- 

 tion of a glass lens produced no effect whatever. Tho test of tho 

 third was simpler still : ho touched a Ions of tho spectacles with 

 the tip of his tongue, and said it was " not cold enough for pebbles," 

 remarking that this was tho advantage possessed by quartz lenses — 

 they were cooler to the eyes. 



Now, is there anything in this ? Does tho question of specific 

 heat really arise ? or is the advantage only that of superior hard- 

 ness, as compared with glass, and consequent loss liability to 

 scratching ? 



Tlien, too, supposing it to bo conceded that quartz is tho bettor 

 material, is anything gained by employing sections cut at a certain 

 angle with the axis of the crystal, as is maintained by at least ono 

 London optician ? Another, of equal eminence, asserts that pro- 

 vided the (|uartz bo pure, free from stria) and bubbles, and uniform 

 in density, you may cut it into slices for spectacle lenses where and 

 how you like. 



Certainly the various appearances which are presented in the 

 polariscope by quartz crystals, according as they are cut parallel 

 to, at right angles, or at different angles with the axis, may indi- 

 cate that it is not immaterial to the lens of tho eye, what section of 

 the crystal be taken. But on tho other hand, tho eyo does not 

 often use polarized light with spectacles. T. S. B. 



THE FIFTEEN SCHOOLGIRLS. 

 [450]— Tho best way t'hat I can think of to manage tliin problem 

 is the following. Designate tho girls by tho letter C and the num- 

 bers 1 to 14. Let one group for tho first day's arran^fement be C 

 1, 2, and set the numbers 3, 5, 9 as tho first members of three other 

 groups. With 3 join any other odd number (not already used), and 

 an even number, which must be, with 7, 6, or 10; with 11, 8, or 14 ; 

 with 13, 0, or 12. With 5 join numbers formed from those with 3| 



