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326 ploring expedition made accurate ob- servations upon a regular series of waves in the region of Cape Horn, and found them to have a height of 32 ft. a length of 380 ft., and a period of 8.7 seconds. Dr. William Scoresby made a report to the British associa- tion for the advancement of science, in 1850, in which he states the results of the observations of waves made by him in the Atlantic ocean in 1848. The greatest distance from crest to crest observed by Dr. Scoresby was 790 ft., and the average distance 559 ft, and the period or interval of time between waves was 16 seconds. This is also found to be the period of waves in the South Pacific ocean in the average seas that are met with between New Zealand and Cape Horn. Observations Upon Sea Waves by United States Naval Officers. THE Marine REVIEW as sights, a pair of parallel lines at right angle to the vessel's keel. The observers at both stations being fur- nished with inter-compared seconds- hand watches, note the instant of time when a wave crest crosses their lines of sight, and they also note how long an interval elapses before the next wave crosses their lines. Comparing their records, they deter- mine (1) the time (say t seconds) occupied by the wave crest in pass- ing over the length (L feet) between their stations; (2) the time (say t seconds) elapsing between the pas- sage of the first and second crest across either line of sight; this time is termed "apparent period' of the waves. Suppose the vessel to be advancing at a speed of V feet per second toward the waves, her course making an angle of a degrees with that course which would place her A large number of observations, exactly end-on to the waves. Then, embracing the height, length, and expressing the conditions algebrai- period of ocean waves, have been cally-- taken by officers of the United States Apparent speed of wave (feet per navy. <A selection of them is here 5, tabulated in order to set forth the second) = -- variations in the observed period: t Wave Year of Force State of sea. Height Length. _ Period. Name of ocean. observation. of wind. Feet Feet. . Seconds. PATA MIG a asta a ieee 6 1886 10 Confused..... 25 375 75 MGI ey pak wile Wine pce eis wie 1885 4 SAO sa cies oiee 25 450 11:0 DO ty oink San tace see 1885 4 Ots sac ses ' 25 500 13.0 NO eeecouc hast die tae ates 1885 4 PeOe easy tine 34 400 12.0 PACH Ole ine viele teat are 6 1886 2 Long swell... 23 350 10.0 aR ree ts es eo 1885 4 Confused..... 22 400 10.0 PRELATIEIC Cs aiasy since to ace x dso 1886 8 Regular...... 21 328 8.0 PCat e. .. Seo eee Oule 1885 4 'Confused..... 21 400 9.0 PGMA Ge eecnon ns gistatt 9403 1886 7 Regular....6 18 318 hae OAT fr we eee te rie a oe sys 1885 4 Confused..... ok 300 8.0 MOMS aaa ce Maes ella ais tei epvds 5 36 1885 4 Ovens ais 3 18 250 9.0 WMO oes OR ao aie ethos leis ous 1885 4 BOO acces EES 18 400 12:0 IDO UA. iow eta eee as 1885 4 AOL le ate ss 16 350 9.0 Oy re a ee eas 20 8 1885 1 (OGiss catea eo 16 350 11-0 LOO gO. oa Sitges 5 ee 88 1885 4 AO sss pots 15 200 8.0 ss fo ics sir Pace el lek clegs 1885 4 Hd. 8 oe ers 15 150 7.0 WB rs ae Ss ee acs ava pede are 1885 4 SdOR UC ie 15 300 9.0 arate Fee nec eal gr oes 1885 4 Ba (ola ie ? 15 250 9.0 WAGCIIC Fie wba els oo eas 1886 4 WOO sonacccs a 12 276 50 (nina Sed f 1 ches ces 1883 5 SEEN ce nee os 11 167 6.8 MPACINC! Seopa Ul eie%'. oe n%e 1883 8 Jereguiar..... 10.5 209 6.7 DON ilar ste een es Sails 1883 6 Confused..... 8 191 6.4 DIO ce die wie ts eee ieee 1886 i Swielle cs wise 8 400 10.0 Pacihe «(South). a. co sco 8s 1883 - 5 Confused..... 8 249° 7.0 PCC ee ieee pieces cece ies a 1885 4 Fe Peto (cSt te ores 8 100 . 7.0 Wace (South) otc: 1885 2 Regulars. 3... 7 100 6.0 One es eure aie ear glee as 1885 3 Be LON e estas es 6 100 6.0 ACTOR ose ce ha alee gs 1885 1 eA Oaa re bse ais 6 80 5.0 NUIAME oak. a hie wee a are 1886 4 Ped Oui sa. 5 261 aan UDO eras wasn tis ates 1886 keg t NEGO dite clea 5 314 8.3 WPACTHC Gia khti eins ee el 1885 1 RO e's tc hes 5 60 5.0 Gatibbedn Sea ia. 1887 3 ECO ek aces 4 100 8.0 POC Cy se ee eae ee ciaiats ts 1885 0 PCO! Gis oe scees 4 50 5.0 GCambbean: Seas cites S65. 1887 3 A Choa ore 3 50 4.0 PAPIAMEICS cists y cies akle es «ene 1887 4 BOO Cee clas 3 30 3.0 (Cavibbean Sea'. ora: 1887 3 RO; det ey 2 40 4.0 Method of Observing the Lengths, Speeds and Periods of Waves. These results have been determined from observations that have gener- ally been scientifically made. A method frequently adopted is to sta- tion two observers, A and B, as far apart as possible at a known longi- tudinal distance from each other on the deck of the' observing vessel. At each station a pair of battens is erected so as to define, when used Real speed of wave (feet per sec- i ond)' = vi={ = --V)cos a t Real" length @p wave (feet) =(V:i + V cos a)t = L cos a. - Period of wave : hcosa 't, Lt; o Vi e v L--Vt August, 1910 In a vessel underway and heading away from the waves, it is necessary to change the sign V in the fore- going equations. Variation of Apparent Period of Waves With Changes in Speed and Course. From these equations it will ap- pear that the interval between the impulses from successive waves re- ceived by a vessel having way upon her and rolling freely, can only cor- respond with the true wave-period when. the vessel's. course:»is.*paral- lel to the direction of the wave crests, and that on all other headings the apparent period of the waves or the interval between the arrival of successive waves at the vessel and the consequent communication of successive impulses to her will vary from the true wave-period with both the speed and the course pursued; and "thus .it)- will at .once:::be,- ob- vious how, in a vessel under control, seamanship may intervene, through a proper management of the vessel as to choice of speed and course, to prevent those destructive effects that are caused by the very deep rolling which may arise from the synchron- izing of the apparent half-period of the waves with the vessel's natural period of rolling. The apparent period of the waves that meet a vessel on a given course may readily be found. The observer takes his plate in' that part of the ship most convenient for his pur- pose, presumably on the bridge; and, having fixed upon a particular object on the vessel's side as a point' of observation, he notes the instant of time of the arrival at this point of each successive wave of a Series. One-half of the mean of the tervals between the instants of time thus recorded equals the apparent half-period of the waves, and, if this is the same as the vessel's natural period of rolling, the correspondence may be changed by altering the ves- sel's course; or, if it is considered that this cannot be afforded, then by alter- ing her speed. If a vessel whose natural period of rolling is -T seconds be steaming, among waves of a length /] feet from Crest. (0. crest, at' a speed of "V¥ ort per second on a course making an angle a with the direction in which the vessel would be end-on to the waves, then, in order that there may be a effect of the in- synchronizing *V is marked plus if the movement is tow- ard the direction from which the waves are coming, and minus if the movement is in the direction toward which the waves are running.