io8 



NATURE 



\Pec, 9, 1875 



900 feet high. Something similar is well known to the inhabit- 

 ants of Arequipa, Peru. The city is built at the base of the 

 extinct volcano " Misti," which rises above the plaza of Are- 

 quipa to a height of about 12,500 feet ; Arequipa itself being 

 over 7,000 feet above the level of the sea. It is not an uncom- 

 mon occurrence (during the fall of the year, February and March) 

 in the morning, from sunrise till about ten o'clock, to see a suc- 

 cession of clouds rolling along the summit from N.E. to S.W., 

 much as if huge masses of white smoke were issuing from the 

 extinct crater. These clouds are either suddenly shot upward 

 by meeting the current from the S.W. and lost at a distance of 

 from 30,000 to 40,000 feet to the eastward from the summit, or 

 else, rolling over the summit, they are carried by the easterly 

 breezes till they become absorbed by the dryer and warmer air 

 of the region to the southward of Misti. 



It must be remembered that between Arequipa and the sea, 

 at a distance of not more than thirty miles, extends the great 

 sandy desert of Islay, having an average breadth of about twenty- 

 five miles, and before the days of the railroad the great terror of 

 all travellers from the rea-coast to the interior. Of course the 

 winds blowing across this desert (a part of the great rainless belt 



of Peru) are greatly heated at all seasons of the year. The eastern 

 slope of Misti, on the contrary, forms the edge of the elevated 

 plateau extending for more than 150 miles to the eastern slope of 

 the Andes, having an altitude of irom 10,000 to 14,000 feet, and 

 the amount of rain falling in this district is very great. 



The formation of the cloud, seen from Arequipa on the summit 

 only of Misti, is plainly seen from the railroad leading to Puno, 

 which, after leaving Arequipa, makes a gigantic sweep north- 

 ward round the Chachami Mountains, and winds its way east- 

 ward behind Misti at a height of about 12,500 feet above the 

 level of the sea. There I have several times seen masses of 

 vapour, condensed into huge white clouds rolling along the 

 slopes of Misti, travel up with great rapidity towards the summit, 

 and either follow its crest as described above, or become at once 

 reabsorbed on reaching the top. This shows plainly that the 

 clouds seen from Arequipa are not due to volcanic action ; the 

 Indians also all agree in stating that there is no tradition among 

 them of Misti having been active. I enclose a sketch of Misti 

 and its cloud from a photograph obtained during my visit to 

 Peru. Alexander Agassiz 



Cambridge, Mass., Nov. 6 



[ The Effect of Waves 



It is generally believed that at a moderate depth the influence 

 of heavy waves ceases, and that during a hurricane all is quiet a 

 few fathoms beneath the surface. If this be correct, why should 

 a swell show such a marked increase in height when it rolls over 

 the edge of soundings ? 



On the parallel of Cape Clear, in longitude 15° W., seamen 

 are familiar with this phenomenon, although the depth is nearly 



five hundred fathoms ; at times it is so marked that the^ dend 

 reckoning may be checked by carefully noting the increase in 

 the depth of the hollow of the waves. Shortly after the edge 

 soundings is passed the sea becomes more regular, and; con 

 quently less dangerous to deeply laden vessels. 



Anyone who has watched during a moderate breeze the co: 

 motion of the water close to a quay wall can form a good ii^ 

 of the ocean when it receives its first check against the Iriih 

 Plateau ; the great waves twist around each other, run up and 

 down in heaps, and then fall suddenly as if bereft, in a great 

 measure, of their forward motion. 



Again, it is a well-known fact that during a " norther " in the 

 Gulf of Mexico the frailest vessels weather out the storm if they 

 can cross the edge of the Campeachy Banks ; a striking proof 

 that at a depth of over fifty fathoms there is sufficient abrasion 

 to destroy the force of the heaviest wave in a very effectual style. 

 On one occasion the writer witnessed this remarkable fact by 

 running from a turbulent sea into comparative smooth water in 

 this locality. 



On George's Shoals, off Nantucket, during a heavy gale, the 

 New York pilots and masters of coasting vessels assert that sand 

 is frequently left on deck after a sea has broken on board, 

 although the depth of water may be twelve or fourteen fathoms. 

 It must require an enormous amount of ebullition at the bottom 

 to raise such dense matter to the surface through such a distance ; 

 for a cubic foot of ordinary sea-sand weighs about 100 pounds. 



In this wild spot the tide, which frequently runs with a velocity 

 of three miles per hour, would assist the lifting power of the 

 wave if running counter to it. During a winter gale, when the 

 strong springs are thus running, tiie confusion of the sea is inde- 

 scribable, although the depth may be thirty fathoms. The short- 

 ness of the sea {j..e. the distance between the crests of the waves) 

 on the banks of Newfoundland, where the soundings are from 

 thirty to fifty fathoms, is noticed by all the navigators of the 

 Western Atlantic, as it reduces the speed of an ocean sieamer 

 more than the heavier waves of deeper water with a similar force! 

 of wind will do. It is evident that this can only arise from the 

 friction of the bottom, as the waves increase in height whea 

 deeper water is reached a short distance to the eastward. 



In the Gulf Stream north of the Straits of Bemine, after 

 "norther" has blown a few hours, the surface of the sea 

 covered with lanes of weed, although only a few patches migl 

 have been seen before the commencement of the gale. As thes^ 

 lanes are often at a considerable distance from shoal water, whicl 

 lies at right angles to the direction of the current and wind, it 

 evident they must have grown near the spot where they floa 

 and been torn from their moorings by the mechanical force ( 

 the waves. W. W. Kiddle 1 



OUR ASTRONOMICAL COLUMN 



The Total Solar Eclipse of 1605, Oct. 12.- 

 Clavius, observing the solar eclipse of April 9, 1567, at! 

 its maximum, remarked " a narrow ring of light roundj 

 the moon which he supposed to be the margin ot the solarl 

 disc." Kepler, however, maintained that this could not! 

 be in reality a portion of the sun, because the moon's! 

 apparent diameter at the time must have been greater 

 than that of the sun, and he concluded, as Prof. Grar 

 relates in his "History of Physical Astronomy," that tht 

 sun must have been totally covered by the moon while 

 the narrow ring of light was visible, a phenomenon again 

 exhibited in the total eclipse of Oct. 12, 1605, which wa 

 observed at Naples. Of this eclipse Kepler says (D, 

 Stella Nova in pede Serpentarii) — "Accurate rectuir 

 fuisse totum Solem, quod quidem non diu duraverit ; ii 

 medio, ubi Luna, fuisse speciem quasi nigias nubis ; cir 

 cumcirca rubentem et flammeum splendorem, a^quali: 

 undique latitudinis, qui bonam cceli partem occupaverit 

 E regioni Solis, versus Septentrionem, coelum obscurun 

 planS, et cum profunda nox est; Stellas tamen nor 

 visas." 



Adopting the same system of elements of the lunai 

 motions, employed in previous calculations of pas 

 eclipses, the results of which have appeared in thi: 

 column, we have the following elements of the eclips( 

 to which Kepler refers : — 



