Jantary 1, 1901.] 



KNOWLEDGE 



Founded by RICHARD A. PROCTOR 



LONDON: JANUARY 1, 1901. 



CONTENTS. 



* PAGE 



The Size of Ocean Waves. By VArnnAx CoBNisn, 



M.SC.(VICT.), F.C.S., F.lt.O.S. ... ... ... ... ... 1 



Monkey HandPrints. Bv K.Lvdekkek. (II lust rated) ... ri 



Photography ■ in Natural Colours.' by the McDonough 



Joly Process. Bv H. Snowden- Waup, f.im'.s. G 



Bird-Love in Winter. By Cuables A. AVitchkll 8 



Notes 9 



Photographs of the Clusters M. 35 and V VI. 17 

 Geminorum, and of Nebulae in Monoceros. By 



Isaac RoBKETs, D.sc, F.K.8. ... ... .. ... ... 11 



'■hotographs of the Clusters M. 35 and 9 Vl. 17 

 Geminorum, and of Nebulae in Monoceros. (Flate.) 



Constellation Studies. — I. The North Circumpolar 



Stars. By E. Waltee Maundeb, F.it A.s. (Illustrated) 12 



Letters : 



l3 HiMAN Life Possible on othek Planets ? By 



Arnold D. Tatloe ... ... ... ... ... 1.5 



PuoTOGRAFHic Search FOR THE Leonids. — E. W. M. .. l.'i 



CONSTITITENTS OF THE SUN. — E. W. M. . . ... ... 15 



Notices of Books . 15 



Books Rkcf.ived ... ... ... ... .. ... 17 



British Ornithological Notes. Coiulnoticl by IIadey F. 



WiTHEKBV, F.Z S., M.H.O.r. ... ... .. ... .. 18 



The Insects of the Sea.— Introductory. Bristle tails. 



By Geo. H. Cabpeniee, b.sc.(lond.) (Illnstrated) ... K» 



Microscopy. Gondiict«d by M. I. Cross 22 



Notes on Comets and Meteors. By W.F. Denning, f.b. a. s. 23 



The Face of the Sky for January. By A. Fowler, f.b A.s. 2.i 



Chess Column. By C. D. Locock, b.a 24 



THE SIZE OF OCEAN WAVES. 



Bj VAUGHA>f Cornish. m.sc.(vict.j, f.c'..s., p.e.g.s., 

 Aseociafe of the Owens College. 



" The heights of wares and their velocity are subjects on 

 which obseirations are never amiss." — T''ide Admiral f// 

 Manual of Scientific Enguiri/. 



Of all the phenomena of our physical environment what 

 is so fascinating j^et elusive as a wave ! Since the earliest 

 days the voyager returned has told about the waves he 

 met, and their bigness, yet even now we cannot get 

 an answer which shall be at once short, clear, and 

 accurate to the question — what is the size of the waves 

 in. a storm at sea? I propose in these articles to 

 describe in some detail what has been done towards 

 answering this question, which, as I know from my per- 

 sonal experience, excites a wide interest. I seek, not 

 to satisfy, but to stimulate this interest, and to. enlist 

 more observers, particularly among those whose oppor- 

 tunities permit of continuous and systematic observa^ 

 tions. Most to be desired are observations from on board 



ship, in deep water far from land, but observations 

 from the sea shore would also bo welcome, and tlioso 

 from lightships and lighthouses exposed to tho waves 

 would be distinctly valuable. 



Obsci-vations of the large waves which disturb the sur- 

 face without affecting the bottom of the deep sea can 

 only be made from on boai'd ship, and arc exti-cmcly 

 difficult to can-y out. Nob only aro the phenomena 

 more complicated than in shallow water, wliero some 

 regularity of direction and of speed is imposed by the 

 limitations of depth, but the conditions on a ship aro 

 themselves unfavourable for this class of observations. 

 The principal things to be obsei-vcd are tho diffcrcnoo 

 of level between ci-cst and trough, or the height of the 

 waves, the distance from crest to crest, or the wave 

 length, and the rate at which the crests or ridges travel, 

 the velocity of the wave, and the interval of time be- 

 tween the amval of tho ridges, i.e., tho period of the 

 wave. The height of the waves would be less difTiciiU, 

 to determine if the ship herself did not rise and fall, or 

 if sho floated as a cork, but in practice she does neither 

 the one nor the other, and the difference between the 

 rise and fall of the centre of gravity of the ship and the 

 rise and fall of the water cannot be calculated tlico- 

 retically. Moreover, the obsei-ver cannot watch tho 

 waves from the centre of gravity of the ship, but has 

 to station himself where the level of his eye is also con- 

 tinually being altered by the rolling, and sometimes by 

 pitching. The eye under these conditions Icses its power 

 of judging horizontality owing to the sudden tilts wliich 

 change the apparent direction of gravity. The length 

 between succeeding ridges is less difficult to observe, 

 for the known dimensions of the ship give a rca,dy means 

 of measurement; or a buoy can be towed astern at 

 the end of a line of known length. Frequently the length 

 from i-idge to ridge vai'ies greatly (sometimes in the 

 proportion of 1 to 2, or even 3) for succeeding ridges. We 

 have ill such cases to do with more than one set of 

 waves, for tho length should vary very slightly for suc- 

 ceeding waves of a single set; the observed distances 

 from ridge to ridge are, therefore, frequently, not wave 

 lengths at all in the physical sense, but casual intervals, 

 tho dimensions of which do not enable us to calculate 

 the velocity of tho ridges by means of the theory of 

 waves. Tho velocities of the ridges must, therefore, be 

 directly measured, which can be done by timing the 

 passage of a wave from bow to stern or from stein to 

 bow, making the necessary allowance for tho speed of 

 the ship and the angle between her course and that of 

 the waves. An accurate determination even of the 

 time of passing the length of the vessel is not easy for 

 a single obsei-ver, and the want of concordance between 

 the ship's course and that of the wave often makes 

 accurate measuromonts of velocity impossible. The 

 best plan no doubt would bo to stop the ship, but as 

 traffic becomes more and more concentrated in big, fast 

 vessels, the difficulty of making the n.ecessar7 arrange- 

 ments is coiTcspondingly increased. In tho case of the 

 liners by which most of us now travel, the waves made 

 by tho ship herself interfere with *he obsei-vation of air 

 but large waves. 



The finest attempt yet made to carry out systematic 

 observations of waves at sea was that of the late Lieu- 

 tenant Paris, of the French Navy ; a pretty full account 

 of who,se work follows, condensed from the original 

 paper in the Rnnie Mnritime ef Cnlnniale, Vol. XXXI., 

 1871. a publication little known to the ma.jority of 

 scientific men m England, and not vei7 easy of access. 

 Next, for comparison, I give a shorter account of the 



