100 



KNOWLEDGE ♦ 



[July 7, 1882. 



k'aiiii; prjitis?— J. W. Bloom, Ed. Wo sliaU bo only too Kind to 

 notioo the ntagnzinc ; as we \vni<>, your letter only to liaiiil from 

 hca"i office. — A&ab. Alas ! we Imro never played Napoleon, and 

 your iinestion is on enigma to us. — U. Sadler. Wo aj^reo 

 with you, and bo, wo fancy, would our friend, F.U.A.S., 

 en further consideration, that thu common proper motion 

 of Castor and • implies that ti.ey art connected. — T. J. 

 llU'KiN. Thanks. (1) It would be a pity were a chance given 

 for " the enemy to blaspheme." Dr. Ball wont rather beyond 

 iho record in saying that if all the planets did not rovolvo 

 in the same direction, the solar system would have perished long 

 ago." Perhaps 1 wont also beyond the record in saying " it would 

 have been as well with the solar system as at present if some 

 planets went one way and some another." Laplace proved that 

 with all the planets going tho samo way round, and all 

 with small inclinations and eccentricities, there could bo no 

 destructive changes in tho solar system. liut, ho never proved 

 Uiat if any even of tho large planets went tho wrong way 

 round, there icouJJ be destructive changes. Dr. Ball, by sa.i ing, 

 " at all events, tho larger planets," shows that ho recognises 

 the quantitative character of tho problem, with which unaly.sis has 

 never dealt in a quantitJitive manner. 1 am satisfied tho revolution 

 of Jupiter the wn>ng way round would do no more harm than that 

 of the earth or Venus — pel haps IcfS, when duo ro»unt isjtaken of 

 the much greater scale of the distances in tho system of giant 

 planets than in that of tho terrestrial planets. Albeit, this has 

 never been ])njved. From the nature of liagrange's etjuations in 

 dealing with this matter, it may be rogirdcd as shown that tho 

 stability of the solar system would not bo absolutely certain, as now 

 (without much moro inrjniry ) if any of the planets went the A-rong way 

 round. (2) Any text book of geography which states that tho varia- 

 tion of the major axis of the earth's orbit has influenced climatic 

 relations, has undoubtedly bluudired. It should bo " minor axis," 

 though the major axis is vci-y slightly variable, in long periods of 

 time, in an oscillatory manner. You quote Mitchell's " Orbs of 

 lloaven," but he was not competent to give an independent opinion 

 on such matters. We find him confounding the parallelogram of 

 velocities with the parallelogram of forces, and making other 

 mistakes equally fatal to his position as an authority. — W. 1'akkeh. 

 It is not easy to say what books would suit you, as tho range from 

 the easiest to the most diffi,;ult is fo great. East and west are 

 different in star maps and geographical maps, because wo look np 

 to the skies and down upon tho earth. N'ote, however, that in my 

 maps there is no right, or left, or top, or bottom ; but the middle is 

 the top, and the bottom is all round.— E. T. C. W. Might yon not as 

 well argue that since the moon affects tho tides, so may Saturn or 

 Jupiter affect the ocean in some other, bat quite as marked, 

 manner? Tho influence of the moon on lunatics, assuming it to 

 exist, might depend in some way on her attractive, luminous, 

 thermal, or magnetic influence ; compare any or all of these with 

 any corresponding influence which any one of tho planets could 

 exert, and you will see that astrology (which assigned much more 

 putent influences to Jupiter and Saturn than to tho moon) cannot 

 possibly derive supjiort, as you suggest, from lunar influences. — U. 

 Wood. 1 referred to pure chance tossing, not to the skilful repetition 

 of precisely identical tossings ; but I said suspicion would be justi- 

 fied. There arc two theories -one that tho coin has two heads, 

 the other that it is a fair coin — on the first tho chance of tho 

 observed cvci^t is 1, on the other it is about 1-milliontli. 

 Hence, the probability of tho first theory comes out, by 

 the formula we gave, very much greater than that of tho 

 second (supposing both antecedently to be equally likely) ; or it is 

 most probable, though not quite certain, that a two-headed coin is 

 Iwing used. If there were any feasible way of explaining as simply 

 the occurrence of twenty tossings always as predicted, though 

 not always of ono kind, precisely the same reasoning would apply 

 to a ca«c where each of twenty to.ssings was in favour of 

 the toi^ser. Suppose, for instance, tho theory to be that ho 

 has one two-headed and one two-tailed coin, and that ho is 

 HI) dcxternos that, while seeming always to toss ono coin, 

 ho in reality changes Ihem at will ; then if ho wins twenty 

 times in soccesHion, the chance of that theory being true 

 would Ije much more likely than Ujo chance that ono coin is 

 used, — even though the odds against )iis being so skilful and 

 aliio so dishonest, were, antecedently, a hundred or a thousand to 

 one.— K. Wood. Dear old Walkinghame-l had quite forgotten his 

 rulf^ (usually very bad) ; but certainly thope you quote for division 

 of decimals are pretty good, though that is an awkward scntcnco — 

 " The 'jw.tient mvit hare »o nwny deriinal jilaccH an the dividend haa 

 more Ihnn the divitnr " — regarded as a general rule, and in connec- 

 tion with the fact that the dividend may havo/fu-cr decimal places 

 than the divisor. — GsAliATiM. Jt is the cii«o that any map can bo 

 iaint«<l in four colours, whatever the number and arrangement (it 

 divisions— only there mu^rt not be, as in England in counties, a part 



of any one county, country, or ahiro within another or separated 

 from tho main body. Tho proof is not very simple— I have for- 

 gotten it. Perhaps some reader may rcnieniher it. I havo not 

 forgotten my promise about precession or limitation of abstrac 

 space. But I have been baflled, so far, by tho constant proceaaioii 

 of new subjects and the limitation of om- concroto space. 



ELECTRICAL. 



William Evans's Swan Lamps can bo purchased for Ss. eaoli 

 (support. Is. extra) of tho Swan Electric Light Company, Mosley- 

 stieet, Newcastle-on-Tyno. To light otic will bo an expensive 

 nuitter. You require twenty good Bunsen cells, quart siao, which 

 can bo procured at 68. each from Ormo & Co., Barbican, 'I'ownson 

 it Mercer, Bishopsgate-street, Griflin & Co., Long-ucro, London, 

 Mottershead & Co., Manchester, or, in fact, any good ])hysical in- 

 strument-makers. To buy tho parts and make the colls yourself. 

 the cost would bo about 3s. Gd. each. These cells will take about 

 151b. of nitric acid (sp. g. 1,420), at 4d. to Cd. per lb., and 4)b. 

 to Gib. of sulphuric acid (good commercial), at Id. per lb. Tho 

 battery will lust three to four hours, and tlio nitric acid may bo 

 used tlirco times, after which it will be too far spent to bo useful. 

 The only other part you require is the wire, the cost of which will, 

 of course, depend on its length. — Constant UtUDKB. OriginaHy 

 enormous battery power was used to work Atlantic cables, but » 

 method is now adopted with excellent results. Each end of tho 

 cable is connected to a condenser ; no current is sent into tho 

 cable, tho signal being transmitted by charging ono side of the 

 condenser from six or eight bichromate cells. 'I'his chargo (sup- 

 posing it to bo + ) induces a — charge on tho other side, and 

 a corresponding •(• charge on one side of tho condenser at 

 the remote end of the cable. The other side of the distant 

 condenser becomes char^'cd — ly, this latter induction actuating 

 the receiving apparatus. Tho resistance of tho older cables i« 

 about 7,uOj ohms, but tho more recent ones are a little loss. 

 Elkctbon. Tho Leclancho cell; soo last week's answer to H. 

 Bardsley.— Timothy Fishku. Tho chloride of silver battery should 

 be charged with a weak solution of ammoniac chloride (sal ammo- 

 niac). Tho zinc dissolves as a chloride, and tho chlordeot silver 

 is decomposed, the metal attaching in a spongy state to tho silver 

 wire, and the chlorine taking the place of that which unites with 

 the zincs. — Jamrs Grundy. 1. Tho machine is not cnlcuhitod to do 

 what you require. Y'ou want a machine wound with thick wire, 

 and offering very low resistance ; considerably loss than ono 

 ohm. 2. 'iho machine will not light two Swan lamps, unless 

 they aro very small indeed. Before I can attem)7t to advist- 

 any particular dimensions, I must know more about tho lampn 

 you mention. What is their reputed candle-power ? 3. Two 

 Bunsens in series would be plenty, but your Leclancho wHll 

 do very well. If tho resistance of tho coil of wire docs not exceed 

 8 ohms, join tho cells in half-series. 4. Your diagram not quite 

 clear. Tho magnets aro of tho horseshoe or U form, and should 

 be so ])laced in tho grooves as to make ono pole. piece a north polo 

 and the other a south pole. 5. Let the magnets come as closely in 

 contact with tho pole-pieces as you po.isibly can. 6. Jumin magnets 

 increase tho power, but you would do better still by u.sing electro 

 magnets. 7. You talk about using a machine where you cannot 

 use a firo for heating purposes. Do not forget that an electric 

 generator used in a coul-inine would, in all cases where naked flamo 

 is prohibited, prove disastrous on account of the spark at tho com- 

 mutator. You mustsend yourcurrnnt into tho minooithcr by means 

 of a wire, or in accumulation. — G. II. Moutimeu. Tho zinc jilato in u 

 Daniell cell should bo { to i of an inch thick. To amalgamate tho 

 plate, clean it in a weak solution of suljihurio or hydrochliiric acid, 

 then rub a little mercury over it. If the mercury does not adhere, 

 wash tho plate again and repeat until thoroughly amalgamated. 

 There are several other methods, but this is the best under tho 

 circumstances. 



CUEMICAL. 



W. H. U. Ydur query is not correctly worded; wo ijroaumo 

 you mean that "the ignition point of ammonia gas is higher than 

 tho temperature jiroductd iiy (not required for) its combustion." 

 It is well known that substances havo to bo heated to a certain 

 point before they will combine ; thus, phosphorus, which burns to 

 brightly in oxygen, requires to bo raised above tho ordinary tem- 

 perature before tho action commences. The heat produced by tho 

 union of tho first few molecules is so intense that the neighbouring 

 ones aro heated beyOnd tho ignition point, and po tho burning 

 procueds vigorously. There are otlier substances that havo very 

 little chemical attraction for each other ; coiiBcquontly their union 

 is productive of very little heat, and also they, as a rule, possess a 

 high ignition point. Now, if ono of these substances bo heated 

 sufliciently at ono point to cause it to burn, as tho heat 

 produced is not sulliiient to raise the tcmpi'raturo of the 



