158 



KNOWLEDGE. 



[August 1, 1892. 



quent navigators contented themselves with corroborating 

 his statements, or striving to gain a reputation as ocean 

 explorers, by attributing fresh wonders to the region of 

 Sargasso. The principle underlying the accumulation of 

 such quantities of weed as are met with, is a very simple 

 one. To quote the words of Humboldt, " the waters of the 

 Atlantic between the parallels of 11° and 13° are carried 

 round in a continual whirlpool." Such being the case, 

 drift-weed must of necessity accumulate within the area 

 of the whirl enclosed by the circle of oceanic currents. 

 Finality, as regards knowledge of the Sargasso or weedy sea 

 of the North Atlantic, is yet far from attainment, but much 

 reUable information has been obtained of late years by the 

 researches of German scientists. The captains of the 

 German mercantile marine have been pressed into the 

 service as observers, and the famous I'lanktmi expedition 

 has also contributed its quota to swell the stock of reliable 

 information relative to this Sargasso Sea. The ancient 

 belief relative to it was that it was a " muddy, 

 coagulated, dense sea, covered with weed which prevented 

 the advance of a ship." Columbus nowhere affirmed 

 that the weed materially interfered with the navigation 

 of his vessel. Oveido, however, does, and in the hands of 

 subsequent writers the density of the Sargasso increases 

 until it becomes a dense mass, an effective barrier to the 

 passage of ships. This idea is, however, long exploded, 

 and the Sargasso Sea of to-day is simply an area of com- 

 parative calm into which drifts the weeds detached by the 

 currents from the shallows over which they flow. This 

 seaweed drift is densest between 70° and 10° West longi- 

 tude and 20° and 35° North latitude, where the Sargasso 

 may be said to cover the surface of the sea to an extent 

 vai-ying from 10 to 2.5 per cent. Outside this ellipse is 

 a region where the Sargasso is less abundantly distributed, 

 and outside that again a zone marked by the presence of 

 still less floating weed, until to the north of the fiftieth 

 parallel of latitude the weed ceases to be found. It is re- 

 markable that the main axis of the Sargasso proper is 

 identical with that of the region of summer calms, with 

 the exception that the latter is continued farther to the 

 eastward. The sources from which the Sargasso weed is 

 derived has always been a vexed question, but the researches 

 of Dr. O. Krummel, of Berlin, have brought the solution 

 within a more appreciable distance than it has ever been 

 before. The Flnnkton expedition of 1889 threw much 

 light on the matter. 



The main supplies of the Fucux natans of Linnaais are 

 now pretty accurately determined. The science of sea 

 botany has discovered that a portion of the Sargasso weed 

 comes from the shores of the Caribbean Sea and the West 

 Indian Islands. Other supplies are torn from the confines 

 of the Gulf of Mexico, while some of the weed found float- 

 ing in Mid-Atlantic has been identified with species 

 attached to the shores of the north of Brazil. That the 

 eastern shores of America produced the weed of the 

 Sargasso Sea was long doubted. Columbus, it is said, was 

 afraid lest the weed should mask some sunken rock, upon 

 which his ships might strike. Others maintained that 

 the " social weed " grew at the bed of the sea, even v.'here 

 the ocean was deep, and that after fructification it easily 

 became detached from the rocks and rose to the surface. 

 The experiments of Bouguers relative to the intensity of 

 the light, which penetrated to a depth of 200 feet below 

 the sea surface, were held to dispose of this theory, because 

 the absence of sunlight in the depths of the sea was held 

 incompatible with the existence of any but hhachcd vegeta- 

 tion. The species of marine weed known as Ltiminaiia 

 lii/rifini has frequently been found to possess a stem over 

 850 feet in length. 



The amount of weed discernible in any part of the 

 North Atlantic varies wth the season. Northward from 

 45° the scattered weed is only encountered in the late 

 summer and autumn, while it fails completely in the 

 spring. The further we go to the south the greater is 

 the mean annual quantity of weed observed, and the 

 increase is pretty equally divided between the seasons. 

 Near 80° N. the maximum of weed is encountered in 

 the winter, while to the southward of 25° the densest 

 season is spring. These facts prove pretty conclusively 

 that the Sargasso floats in summer time from the current 

 of the Gulf Stream in a south-easterly direction. The 

 rate which this drifting weed assumes in travelling along 

 the convolutions of its course, until it becomes merged in 

 the region of densest Sargasso, varies considerably ac- 

 cording to its distance from the coast of Florida. 

 Supposing a bunch of weeds were detached, say, from the 

 Bahama Eeef, it would require a fortnight in which to 

 make the journey to Cape Hatteras. The next portion of 

 its voyage — north-east, to the sixtieth degree of west longi- 

 tude — would be accomplished at about half the siJeed, and 

 would occupy a month to perform. From 60° W. to 40° W. 

 the speed would have fallen to half-a-knot per hour, and 

 the 950 knots would take ten or eleven weeks to traverse. 

 From this point there are approximately GOO knots to be 

 covered by the now heavy and saturated weed before the 

 south of the Azores is reached. The weed now moves at 

 the rate of seven or eight miles per day. When this point 

 is reached the weed moves still more sluggishly, and 

 gradually becomes merged in the dense Sargasso, where its 

 only motion is an undulatory one, produced by the motions 

 of the Atlantic swell. How long the floating weed en- 

 countered in the centre of the Sargasso Sea remains upon 

 the surface is not known, but much of it when it takes up 

 its position there is extremely water-logged, and soon sinks 

 to the bed of the sea, to make room for fresh supplies of 

 fucus. 



Such is a brief summary of our present knowledge of the 

 current system of the North Atlantic. It is far from 

 perfect, and wiU probably continue to be so until the 

 observing powers of the average British shipmaster are 

 more scientifically developed than they are at present. 



THE FACE OF THE SKY FOR AUGUST. 



By Herbert Sadler, F.R.A.S. 



GEOUPS of sunspots of considerable magnitude 

 continue to diversify the solar surface. The 

 following are conveniently observable minima of 

 Algol : August 9th, llh. 26m. p.m. ; August 12th, 

 Bh. 16m. P.M. 

 Mercury is too near the Sun to be conveniently observed 

 in August, being in mferior conjunction on the 26th. 



Venus is a most conspicuous object in the morning sky, 

 and is at her greatest brilliancy on the 15tli, more than 

 three times as bright as she will be at the end of the year. 

 She rises on the 1st at 2h. 28m. a.m., or lb. 58m. before 

 the Sun, with a northern declination of 16° 46', and an 

 apparent diameter of 46", about j^ths of the disc being 

 illuminated. On the 12th she rises at Ih. 50m. a.m., or 

 2h. 33in. before svmrise, with an apparent diameter of 38^", 

 and a northern declination of 17° 11', exactly one quarter 

 of the disc being illuminated. On the 31st she rises at 

 Ih. 24m. a.m., or 3h. 49m. before the Sun, with a northern 

 declination of 17° 26', and an apparent diameter of 29:}", 

 just four-tenths of the disc being illuminated. About the 

 time of the planet's rising on the 11th an 8i magnitude 

 star will be about 1' north of Venus, and on the morning 



