Aprils, 1875] 



NATURE 



445 



underneath the observer, and the distance from crest to crest 

 1,125 f''i ^""^ ^° '^^^ °"^ would be one-tenth of the other. 



It may be suggested that such measurements would be more 

 reliable if taken from a point above, on the tops or shrouds of the 

 masts of a ship (z'ide Admiralty Manual, p. 94, for directions), 

 so that one could just get a view of the upper horizontal level, 

 so as to see the crests of the other waves advancing. 



This computation of wave height much exceeds previous 

 recorded observations by double the amount, so that there may 

 be some error in apprehension, or in statement of the account, 

 or in the calculation. 



Dr. Scoresby's observations in the North Atlantic record 

 24ft., 30ft., the highest 43 ft., and the mean 18 ft., in westerly 

 gales ; and the frigate Novara, 20 to 30 ft. off the Cape Pro- 

 montory. 



French observers in the Bay of Biscay state a height of wave 

 ofj36ft. ; Capt. Wilkes, U.S.N., writes of 32 ft. in the Pacific, 

 and Sir J. Ross of 22 ft. in the South Atlantic. 



Heights of waves in N. W. gales off the Cape of Good Hope 

 were computed at 40 ft., those otT Cape Horn at 32 ft., in the 

 Mediterranean seas at 14 ft. loin., and in the German Ocean at 

 13^ ft., but in British waters they are only found to average 

 8 to 9 ft. 



The velocity of ocean storm waves was observed by Dr. Scoresby 

 in the North Atlantic to be about 32 miles per hour ; Capt. 

 Wilkes recorded it at z6\ miles in the Pacific, and French sailors 

 in the Bay of Biscay at 60 miles an hour ; and I have noted it 

 myself ill the South Indian Ocean at 224 miles an hour in the 

 great westerly swell after gales. 



Further, Dr. Scoresby has estimated the distance between or 

 breadth of his Atlantic storm waves at about 600 ft. from crest 

 to crest, which is only about half of that stated in the letter, 

 and with a proportion of only Jj for height to breadth. ( Vide 



Report, British Association, 1850.) Dr. Scoresby st ites that his 

 waves of 30 ft. in height move at the rate of 32 miles per hour, 

 which hardly accords with the observers of no ft. in height, 

 with 25 miles per hour of motion. It would be very desirable 

 that more data should be got on storm waves, for here is another 

 discrepancy of proportion of length to breadth of iV to ^V,, which 

 cannot be surely common or correct. 



The accompan; ing diagram is constructed according to Dr. 

 Scoresby's scale of measurements, 600 ft. breadth, 30 ft. height, 

 and 220 ft. vessel, witli rates of wind, wave, and vessel, and from 

 it one may ponder on what small dimensions these terrific looking 

 waves are constructed, and that a ship after all looks only like a 

 coik or chip on the great seas. 



The account of the peculiarities of storm seas, also therein 

 mentioned, from the S.W. and N.W. directions in the Atlantic, 

 may be extended to the effects of other winds elsewhere on the 

 ocean surface. 



North-east gales in the North Atlantic, and south-east ones in 

 the South Atlantic, appear to have similar effects on the seas 

 and vessels exposed to them. 



The waves raised are short, brisk, feathery, and clear, and 

 make a peculiar rushing din, and they do not cause a ship to 

 plunge so much as to roll, and are not accompanied by wet so 

 much as by dry weather. 



They are generally not dangerous to navigation in the open 

 sea, as they carry light, clear, swift driving clouds, which do 

 not obstruct marine observations or a view of the horizon all 

 round. 



On the other hand, the north-west gales in both hemispheres 

 are attended by heavy, dark, rol ing waves of huge bulk, momen- 

 tum, length, and breadth, up which a ship is driven like up a 

 hill-side, »nd down which it scuds as into a valley. 



Here the vessel plunges more than she rolls, and is subject to 



lurches on one side or other, and labours much in consequence 

 of the wetness of the sails and rigging, increasing the weight of 

 the top hamper and its hold by the gales. 



These winds are more dangerous to navigation, as they are 

 accompanied by thick heavy clouds lying low in the atmosphere, 

 and shedding much rain and obstructing the view of the horizon 

 all round, and so prevent marine observations by day or by 

 night. 



The grand westerly gales of the northern hemisphere, seen on 

 the passage to and from America, occur amongst the latitudes of 

 the counter trades, and are reciprocated by the similar belt in 

 the southern hemisphere below 40° latitude, and are called by 

 Maury the " brave west winds." 



This region is traversed by the Australian and New Zealand 

 liners, south of the Cape, and the voyages along this tract are as 

 exciting as a race, and the ship is in much the same predicament 

 as the man in the song with a steam leg. 



As much sail as can be safely and possibly carried is spread, 

 as speed is a vital necessity in order to keep the canvas and 

 rigging from being blown away, and to prevent the ship being 

 pooped by a following wave. 



The frail bark then boldly scuds along before the wind, down 

 one mountain wave and up another, with cordage creaking and 

 masts bending, as fearless as the wild albatross following in its 

 wake, or the gay porpoise careering in its front. 



The difference to the passenger between these two classes of 

 winds seems mainly to depend upon their wetness or dryness, so 

 that the rainy weather adds to the discomfort of the one and the 

 clearer weather in the other gives him some consolation in the 

 storm. 



The ship itself would no doubt have a preference, while in the 

 one case its canvas and cordage are soaked with water and its 

 decks deluged or sloppy ; in the other its rigging is allowed to 

 retain its natural trim, or even to get slackened by over-dryness, 

 and the decks remain comparatively dry. 



As to the waves themselves, it still remains to be explained 

 why they should be greater with winds laden with rain than with 

 dry winds, in the open sea and far away from land, unless the 

 weight of the atmosphere above them should be allowed to count, 

 as the barometer rules higher of course in the north and south 

 easterly winds than in the north or south westerly gales. 



Admitting there might be a difference in certain instances, 

 even over the same tract of latitude, of one inch in the height of 

 the mercury in the barometer between westerly and easterly 

 gales, we may find on calculation that this would make a differ- 

 ence of 896,091 tuns of weight of the superincumbent atmosphere 

 on the surface of a square mile of the sea. This difference of 

 atmospheric pressure would cause or allow a greater mobility to 

 impression by the winds in the seas outside the tropics and under 

 low barometric indication anywhere, and also a tendency in them 

 to flow in towards these regions, and into storm tracts, as is 

 narrated in accounts of cyclones, where great floods are sometimes 

 produced. 



The movements of the ocean swells after gales, it may be 

 hazarded, might be accelerated by the tendency of the disturbed 

 equilibrium to restore itself in the efllux of the seas from the 

 storm region to calmer exteriors. 



There might therefore appear to be as much movement and 

 commotion in the waters below as there are in the atmosphere 

 above, in all disturbances of the equilibrium mutually arranged 

 between these two fluid coverings to the surface of the earth. 



Edinburgh J. W. Black 



Walker's System of Geometrical Conies 



It is remarked in Nature, vol. xi. p. 404, that Walker's 

 " generating " circle appears to have dropped out of recent text- 

 books ; but I may be allowed to add to the statement of your 

 reviewer that Walker's method was revived in the jTh-sscnger of 

 Mathematics, vol. ii. p. 97. I had been acquainted with his 



