48C 



• KNOWLEDGE ♦ 



[Dec. 22, 1882. 



A LIMIXOUS SEA. 



''''■■'■ \S :'! n stMOt to om- ur two anioles in your colamns re- 



' \ beg to pvo a sli^rbt accxiuiit, viz., duriuff a run 



:. y tonanls the Ued Sea — making Socotra — I paid 



f Its intense phosphorescence ; in one place wo ran 



u : , with a splendid white sea between long. 60J° and 



Ik'i , a^J ;.p-.uu 'M between long 56° and 52*, latitude varying from 

 It;" to 15' north. The deceased W. Sj-mington, F.R.G.S., com- 

 mander of S.S. //iinioir, whose command I had the pleasure to 

 be under, gnve it as his opinion that the phosphorescence extended 

 several feet below the surface, which is my opinion, but to what 

 extent more scientitic research was requisite. I should like some 

 of oar Ecientilic men to give an explanation in your columns of the 

 - -I'fKjecd causes and depths of luminous seas. S. J. H. B. 



Ot!"]— From my diary of what I observed in the Mediterranean : — 



< >ct. 29. Off Cobo de Guta. The sea very luminous ; the ripple 

 at the bow of the steamer full of shining bodies apparently an inch 

 and upwards in diameter. These became visible only when the 

 cutwater threw up the foam. "Jellyfish" were shining brightly, 

 apjiarently some feet below the surface. They became extremely 

 brijrht when approached by the vessel. Two large fish (porpoises ?) 

 skimmed athwart the course of the ship, showing parallel furrows of 

 coliiurcd light, which ceased as they sank beneath the vessel, and 

 renp|>eared as they rose to the surface again on the other side. 

 Their wake continued to sparkle for a couple of seconds after they 

 had |iasscd. Another porpoise swimming at the cutwater looked 

 from above as if filled with pale opal light — without flashes, except 

 when his fins or toil cut the surface. 



Nov. 1. Alicante. Aa the vessel lay in harbour, the still water 

 in the deep shadows looked almost black. Shoals of small fish were 

 playing on the surface, showing themselves by ripples and sparks of 

 light. The oars dripped golden spray when lifted at each stroke, 

 and the light produced by the ripple against the boat's side and the 

 fingers of a luind trailed tlirough the water was sufficient to enable 

 cue to distinguish small objects, but not to read print. 



A handful of gravel thrown into the harbour produced a pretty 

 Fparkle, and a flat stone skimmed along the surface raised a bright 

 flajih at each skip. The water was dark except when disturbed, but 

 jellyfish could be distinguished shining, apparently at some depth. 



Both nights were warm and very still. Barometer about 301 in. 

 M.S. 



anstorrs to Coiie^^ontitnti* 



ThUttclion is limilcd to one column as the maximum. Only a 

 tmall proportion of the letters received can, therefore, he answered 

 here. Uany net answered may nevertheless be noted and acted 

 vpon. Letters Taitin^j religious, palitical, or personal questions, 

 atkinj for teit.hnfik information, proposing class-room problems for 

 tolulitm, and so forth, pass at once to a receptacle specially provided 

 for them. A stern and infiexihle censor has been specially appointed 

 to stand between a too-yielding Editor and those who thus unreason- 

 aUy claim hit attention and space which should he otherwise occupied. 

 No LETTEBS AKSWEBED TIIKOrCH THE POST. 



lEi.N PvEiTE-s.— In reply to " D. and M.," p. 422, this is of some 

 value for the sulphur it contains ; its value as an iron ore is spoiled 

 by the sulphur, the process of separation being too costly j it has 

 a market value. (C. G. P.) — A. K. Your qnerj- should have been 

 answered before, but there has been some diflieulty in obtaining 

 pntiw information. Alum cake is a specially-prepared body. It 

 is II. .i.uf.vt'iri'l from china clay, free from iron. This substance is 

 "f alumina, produced by the decomposition of 

 T clay is calcined in a furnace, and then treated 



^ l.iiric acid to combine with the alumina present, 



■'■ of alumina according to the equation: — 

 ■'■t.3H^SO^-A1^0,(SO,)3 + 2Si(J;-^5U,0. The 

 I ■ ■< place is a verj- violent one, necessitating the 



'I with water. The mixture Ixjils violently, 

 y ■ ■ thicker, and finally a solid porous mass, which 



i- I- rf.. •;. <]rv. T)ie water it contains combines with the sulphate 

 of alumina. The whole of the silica of the clay is still present, 

 \nt n in nn impalpeble form. — Certo. Your query with reference 

 t.. . ,t.,r,„ . , •. ..roving "Avogadro's Law," deals with a subject of 

 • t. We will ask Mr. Jago to supply for our chcmi- 

 - m the subject.— Ac/iA. Soft water would not Ijo 

 ' ■ '-' through either a pump or leaden pipe. Hard- 



tit--- .. .1 ,. ., I Til- prcaencc of salts of lime or magnesia. The car- 

 |y.iiiat«« lA tiio»e boMii are held in solution by carbon dioxide gas, if 

 present in the water. The tulphatca of lime and magnesia are 



themselves soluble. As carbon dioxide is exi>cllcd from water by 

 boiling, tho carbonates are then deposited arid the water thereby 

 softened. This treatment docs not afTcct sulphates. Try whether 

 tho water in question is softened by boiling j if so, tho hardness is 

 only " temj>orary " and can be removed by tho addition of a proper 

 quantity of slacked lime, stirring tho whole up, and then allowing 

 it to settle. It \\u)uld bo well to get tho hardness determined by a 

 chemist, who would also inform you as to the proper quantity of 

 lime to add to, say, ten or a hundred gallons of water. This is an 

 economical and simple process ; it would not, however, effect tho 

 removal of hardness duo to sulphates. — Harroviensis. Your best 

 plan will be to go to some gentleman )>rofeBsionally engaged in 

 teaching chemistry, and who has had experience of technical 

 analysis. Mr. Jago, of the Science School, Brighton, might bo able 

 to help you. 



ELECTRICAL. 



P. W. Halfpenny. See article on " Griscom Motor" in Know- 

 ledge, No. 54. How many machines do you require to work ? Are 

 they all in one room, or distributed over a building ? — Ckanleigh. 



1. See answer to C. J. B., &c. 2. No. — James Gkundy. 1. Mr. 



B. S. can doubtless sujiply what you require. Write and ask him. 



2. About two-thirds of a pound to each plate. 3. I wrote from my 

 office for a price-list from which I quoted, but which apparently 

 gives wholesale prices. 4. Glad you appreciate it j tho dynamo 

 will bo described in a week or two. — Fbbd. W. Foster. I take it that 

 by far tho greater portion of tho readers of Knowledge are neither 

 dunces nor wiseacres, but jieoplo of fair intelligence, who, having a 

 little knowledge, desire more, and that, having been once informed of 

 the meaning of a particular term, do not wish every reforenco to that 

 term to be accompanied by an elaborate definition. Granted that 

 the article in question contained technicalities, there were none 

 which had not boon jireviously explained. Certain expressions are 

 furthermore imperative, as, for instance, electro-motive force. Were 

 I, instead of this term, to substitute "tension "or "intensity," I 

 imagine that we should receive sufficient letters condemning tho 

 crime to fill Knowledge for a month. Let me assure you that 

 technicalities are avoided as much as possible, their use being 

 confined to those occasions when the adoption of any other 

 term would lead to misap])rchensions or such-liko difficulties. — 



C. J. B., Hion McMaster, F. Clapham, Split Ring, W. H. Dkuce, 

 and P. C. Agent, Mr. Heap, 2, Scott's-yard, Bush-lane, Cannon- 

 street, E.C. £3. Is. ; with batterj-, £6. 5s.— C. S. B. Presume you 

 have some foundation to work upon. Surely you have a public 

 library in Leeds, and should, therefore, be able to choose for your- 

 self. To gain a " thorough " knowledge of electricity alone, 

 ignoring altogether the other subjects you enumerate, you would 

 require more books than have yet been published. Our rules forbid 

 my mentioning any particular works. — E. A. F. In all probability, 

 yes, but I have no record of any electrical disturbance on tho fith 

 ultimo. — Tnos. F. Woodhead. A few advertised, but I cannot say 

 if the one described is on sale. 



JiTiTER. Tide text-books on astronomy. — H. M. How does that 

 prove boy not electrified by artificial means ?— F. Selbv. It has 

 been tried ; but no satisfactory arrangement could ever be made. — 

 Iota. (1) As near as I can make out, the next total eclipse visible 

 in England viiW occur in 2090, shortly before snusct, total only in 

 tho south-west counties. As tho time draws near, the Editor of 

 Knowledge will give full instructions for observing it. (2) The 

 author of " How to Got Strong" replies that, not being medical, he 

 cannot give advice about preventing " stitch in tho side ; " but it is 

 seldom noticed except when running or walking after a meal, when 

 it is better to let the stitch prevent exorcise, than to take exercise 

 to prevent tho stitch. — G. II. S. Dimensions of Martian satellites 

 not known. Periods, 301i. IGm. and 7h. 38m. ; distances from 

 centre, 14,530 and 5,K00 miles for Deimos (tho outer) and Phobos, 

 respectively.— W. Simmon.-;. Thanks; quite agree with you.— Kobt. 

 H. Mu.snENS. Thanks ; see "Gossip."— R. B. G. Have you tested 

 your theory by a little calculation. The sun illuminates one 

 hemisphere of the moon, plus — how much ? Answer, a none a 

 qtiarter of a degree in width. How wide would this look when near 

 tho edge of tho lunar disc ? Even at tho middle it would bo about a 

 450th part of the moon's diameter in breadth ; near the edge less 

 than the 2,000th part. — T. A. Your position cannot be assailed — 

 by me. — Sidney Tavick. So much more space than can lie spared. 

 — CKASLEion. (1) If comets bo the fuel of the son, he needs stoking ; 

 (2) Menacing Comet (?) not same as Tewfik's; (3) " If several 

 comets appeared at tho same time," two or three would be visible at 

 once. Know of no other consequoncos ; (4) There is but one R. A. 

 Proctor, and he is his own editor. — Dgon Pahbie. I certainly am one 

 of the false scientists, if what your friends say is true. Wo are in a 



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