March 23, 1883.] 



KNOWLEDGE 



183 



Any one wishing for further information may w-ito to mo at my 

 town addrpFi.i. 34, Comwnll-road, or my precent one ; or to mj- 

 bnsineBS atrent for the Exhibition, Mr. John Flack, 74, Great Queen- 

 street, Lincoln's Inn-Fields. E. M. King. 



STEAMERS' SIDE-LIGHTS. 



[767] — Does not the accompanyinp; sketch offer a simple solution 

 to the difficulty of ascertaining another ship's course at night '< 

 The separate combination of lights, i.e., green and white, green 

 Trhite and green, or white and green, would respectively show the 

 angle of any other ves.iel to your own. A system of many lamps, 

 as has been snggested, bears grave objections ; .simplicity being, in 

 this matter, more than needful. C. H. Brockklbank. 



_C£^?A j 



[There seems to me no reason why three side-lights, in the form 

 of an equilateral triangle, should be regarded as at all less simple 

 than a single coloured light. They would show a great deal 

 further, indicate by the shape of the triangle the side they were 

 on, the ship's position, her distance, and so forth. Coloured glasses 

 cut off a large part even of a single light's rays. — B. P.] 



ALTERATIOX IN COAST LIJTE AND SUBMERGED 

 FORESTS. 



[768] — A ** Southport Resident" (701) imagines that I antici- 

 pated in my query {l>73) that Southport was to become an inland 

 town all at once, and he says there has been no retrocession of the 

 sea for fifty years, which proves that no alteration is taking place. 

 He admits changes are taking place all round Lancashire, and that 

 a fringe of sand varying in breath up to a mile has been formed by 

 this retrocession ; but it is on this fringe of sand that my observa- 

 tious were based, and the continual increase of which I anticipated 

 would eventually alter the coast line. 



The low water-mark is a remarkable one from the estuary of the 

 Dee round to Morecarabe Bay — the water ebbing rapidly in places 



leaves large areas, which probably will, in tho course of time, 

 become dry land. 



On the east coast of England, in many places, tho water is 

 gaining at the rate of about 3 ft. a century ; but I should think the 

 exactly opposite action going on round Sonthpnrt must be more 

 rapid than this. 



Some great changes are taking place in the Isle of Sheppoy, on 

 the north of which tho water gains so fast by tho continual giving 

 way of the cliffs that tho old church of Warden has been almost 

 destroyed, and at tho present rapid action going ou Minster Church, 

 which is such a conspicuous object for so many miles rouud, and 

 which is only a mile and a-half from the sea, must eventually 

 succumb to the same fate. 



I was not aware that there was a submarine forest at the estuary 

 of the Mersey, but such forests are very freiiuontly met with else- 

 whore, and they tell us, in the same manner that a seam of coal 

 does, of the submergence which has taken place in tho case of the 

 latter, probably begun some hundred thousand or more years ago, 

 assuming that these changes are brought about by a gradual process. 



An ancient forest was discovered some tim" ago at a great depth 

 in the dockyard at Sheemess, whilst a well was being snnk. On 

 parts of the Cornish coast, at low tide, stumps of trees may be seen, 

 which are proofs that a submergence is tivking place there. I may 

 add that the cliffs at Shcppey arc composed of London clay, and are 

 very prolific of fossil remains, some gigantic species of turtles, I 

 believe, having been brought to light by the continual exposure of 

 fresh land. H'sett. 



THE SCHOOL-GIRLS' TUOBLEM. 



[769] — Here is a symmetrical solution of puzzle 725, p. 106. I 

 shall be curious to know if my method is the same as that of yonr 

 correspondent : — 



Day 



The series re-enters to day I. by formula given below — 

 The twenty-one girls are divided into three groups of 7, and 

 called 81 a.. ... a- b, bj.-.b;, kc. Tho first three rows on days I. — VJI. 

 exhaust all combinations of form a a a, b b b, c c c, and the rest 

 are in form a b c. 



Assuming order in day I., tho following formula gives order for 

 days II. — VII. If a, occupies a given place on any day the girl 

 in corresponding place on next day will be 8,4-1, subtracting 7 

 when tho suffix exceeds that number. Similarly, b,^o takes the 

 place of b, and c,+3 of c, — e.g., on day III. Cj comes in column 3, 

 row G; so, in same place on day IV. we have Cs(a_7 = Ci. 



Days VIII., IX., X., are formed by reading tho first three rows 

 of days I. — VII. downwards, and of the rows thus formed taking 

 1, 4, 7, &c., for day VIII., 2, 5, Ac, for IX., and 3, 6, &c., for X. 

 For these three days the above formula applies to any girl and the 

 one above — e.j., day IX., column 3, row 5, 05 = 00+3. 



East Maesdex. 



LETTERS RECEIVED. 

 A. M. D.— A Fellow.— F. R. A. S.— Nemo.— W. Grandy.— Facic- 

 bat. — D. W. Staniforth.— Senex. — Solarium. — C. Jacobus. — R. K. 

 Stephens. — A. F. — A Subscrilwr to Knowledge. — Lenses. — Boston. 

 — S. E. Clark.— J. A. Robson.— H'sett.- E. B.— B. Blackburn. 

 Difficult to say if eddies would occur in currents so vast. — J. B. W. 

 Mr. Browning will do this. — J. L. Wolff. Rather unsuitable subject. 

 — C. H. — (;. Duncan, Sec. Cannot get those numbers myself. — 

 H. H. D. Thanks, but the general character of forecasts now 

 fairly indicated ; and space runs short. — Silva. — J. II. C. — Faciebat 

 (4c.). Thanks. How much more useful such discussions of 

 translations than the old-fashioned way, which left no time for 

 them.- F. R. A. S.'— P. A. Pierson.- A. N.— W. J. King.— J. C. 



