MEASURING OCEAN WAVES.

Mataura Ensign, Issue 945, 14 September 1901, Page 3

MEASURING OCEAN WAVES.

Mr. Vanghan Cornish writeson " Wave Measuring " in the current nnmler ol " Knowledge," and mentioning hie difficulties of obtaining good results, lie says:—" . , . two successive waves rarely ran in exactly the same direction, and that, with a heavy following sea the ship yawed about so much that the angle between her course and that of the waves could only be estimated approximately, Keally big waves weie met with on only tfcreedays. On June Bth, 1885, in lat, 47 deg. S., long, 175 deg. W., the sea was too irregular to measure individual wave heights ot lengths, but the barometer indicated about 12'5 feet vertical motion of the point of observation below decks. The surface of the sea was pretty ion stantly about 7 feet below the port-hole in the troughs, and 1 foot at the crests. This Ogives an average height of the waves 18-5 feet. The velocity of I lie waves was pretty eonftaut, although Hie length appeared to be so irregular, live observations giving spesds of 29, 28, ?i, 33, and 30 miles per hour (average inri miles). On June 101 hj, in lat. 51 1\< ?. S.. long. 160 deg. W., the observer availing himself of the previous determination, assumed a constant diHori n. <• if aix feet; between the height of llio aneroid above water level at cm t and trough, and added thij to the olwinid variation of the aneroid. Indivi'it <il waves were observed with heights of 20, 21. 23-5, and 26 feet, but the. indication of the aneroid indicated that the diligence of absolute level between the low.: t trough and the highest crest (not one of those recorded above) was 35 fei t. 1 suppose the inference from this to be that the difference, if a real one, was due to the presence of a long swell susceptible but not visible in the lough sea, and I apprehend that the revelation of Buch invisible but not negligible waves is one of the special advantages :>i the aneroid over eye observation. The velocity and length of waxen wrni measured just before the heights were taken ; three determinations gave the following rasults : Velocity. Length. 32 miles per hour 507 feet. 35 „ 470 „ 39-5 „ _ 28'S .. 358 „