206 



NATURE 



[June 29, 1S82 



pared with the former, though according to Helmholtz's 

 theory their tones should be alike. It may be objected to 

 these illustrations that in all natural sources of tone one 

 never finds a whole series of partial tones every member 

 of which is equally loud as the fundamental tone. It 

 is more nearly true for most musical instruments that 

 the higher up one goes in the series of partial tones 

 the feebler are they in comparison with the fundamental 

 tone. 



Accordingly, Kcenig has combined, as in Fig. 2, a series 

 of partial tones corresponding to the respective frequencies 

 •j 3> 5> 7> 9> making the amplitude of each partial tone 

 inversely proportional to its frequency. The separate 

 curves are shown in Fig. 2, both grouped about a hori- 

 zontal line, and also as successively superposed upon the 

 fundamental. The uppermost of the set of curves ex- 

 hibits the final resultant ; which, in this case, where the 

 difference of phase is taken as nil, and all the components 

 rise from zero together, is seen to consist of bold, well- 

 rounded sinuosities. In Fig. 3, curves identical in wave- 

 length and amplitude, but differing in phase by {, are 

 compounded together ; but the final resultant shows a 

 wave-form that is practically a zig-za^. Now if these 

 bold sinuosities and zig-zags be cut out in thin metal and 

 curled up into circumferences so as to adapt them to use 

 as wave-sirens in the manner before-mentioned, it is 

 again found that the zig-zags corresponding to differences 

 of phase \ and f yield always harsher and louder tones 

 than the rounded sinuosities that correspond to o and h. 



These observations are very remarkable, and have im- 

 portant bearings that must be left for discussion in the 

 next article on Kcenig's work. 



For the present we will conclude by observing that 

 more than once it has been pointed out that a certain 

 perception of difference of phase did exist. Sir W. 

 Thomson has suggested that there is evidence of this in 

 the phenomenon of slow beats which by a curious 

 acoustic illusion almost always suggest the idea of some- 

 thing revolving. The writer of this notice had also pre- 

 viously pointed out that in certain cases where a compound 

 sound was led separately to the two ears a difference of 

 phase between the components could be detected. 



It may not be generally known that Dr. Kcenig has 

 quite recently republished under the title of " Quelgues 

 Experiences d'Acouslique" the most important of his 

 recent researches, including those on the Wave-Siren 

 and on the Beats of Imperfect Consonances. The figures 

 herewith presented, and those which will accompany the 

 continuation of this notice, are taken by Dr. Kcenig's 

 courteous permission from this his very valuable con- 

 tribution to experimental acoustics. S. P. T. 



THE RAINFALL OF THE GLOBE 

 "DROF. LOOMIS has recently contributed a paper on 

 *■ this subject to the American Journal of Science of 

 no small interest and value. The paper gives the mean 

 annual rainfall at 713 places in all parts of the globe, and 

 the results are graphically represented on a map of the 

 world as closely as can be done by five tints of one 

 colour. These tints represent respectively annual amounts 

 of rain under 10 inches, from 10 to 25 inches, 25 to 50 

 inches, 50 to 75 inches, and above 75 inches. It is stated 

 that the map is merely a provisional one, it being Prof. 

 Loomis's expressed intention to publish a list of addi- 

 tional observations with a revised edition of the map ; 

 and in the meantime he invites the assistance and criti- 

 cism of meteorologists in furtherance of the work. 



The map shows unquestionably the broad features of 

 the geographical distribution of the rainfall of the globe, 

 so that any changes that will be made in a future issue, 

 however interesting and important these may be locally, 

 will only be rectifications of the iso-hyetal lines in some 

 of their subordinate details. 



Leaving out of consideration all exceptionally reavy 

 rainfalls confined to limited spots, such as those of Chera- 

 punji, in Assam, which amounts to 492 inches anrually, 

 and the Stye, in Cumberland, which is about 190 nches, 

 the heaviest rainfall is met with in the rain-belt which 

 surrounds nearly the whole globe lying between thf north- 

 east and south-east trade-winds. Absolutely the largest 

 rainfalls over large regions are to be found w'lere the 

 trade-winds, after having traversed a great bieadth of 

 ocean, are forced against and over a breadth of land, of 

 some elevation and extent which lie across their path. 

 Of these the best examples are the highlands of Java, 

 Sumatra, and Assam, in the Old World, and parts of the 

 north of South America, and of the steep slopes of Mexico 

 facing the Gulf of Mexico in the New World, over which the 

 trades or monsoons discharge their moisture so copiously 

 as to raise the rainfall over large tracts up to, and in 

 cases considerably above 200 inches annually. The 

 influence of height is well illustrated by the rainfall of 

 Mauritius ; thus, while at the observatory it is 46 inches, 

 it amounts at Cluny to 149 inches on a mean of the same 

 19 years. Similarly in St. Helena, while near the sea- 

 level it is only 5 inches, at a height of 1764 feet it is 48 

 inches. In Ascension, no part of which rises to any con- 

 siderable height, the annual rainfall is only 3 inches, and 

 the whole island is little else than a burned-up desert. 



The rainfall is particularly large in mountainous regions 

 in both hemispheres above lat 40°, situated on the eastern 

 shores of the great oceans, and consequently in the full 

 sweep of the strong westerly winds of these high latitudes. 

 Thus large portions of Scotland north of the Clyde, one 

 or two small patches in England, a few spots in Ireland, 

 large tracts between California and Alaska, the south of 

 Chile, and the west coast of the south island of New 

 Zealand have an annual rainfall exceeding 80 inches. 

 Nay, even at Bergen, lat. 6o° 23' N ., bathed in the warm, 

 moist, westerly winds of the Atlantic, the rainfall is 73 

 inches annually, which is the largest rainfall yet observed 

 anywhere at so high a latitude. Those headlands, even 

 though of comparatively small height, which ran out into 

 the sea, meeting the moist oceanic winds, have rainfalls 

 very considerably above the average— owing doubtless 

 largely to the greater friction of land than water on the 

 winds, thus partially arresting their progress, and in- 

 ducing a more copious precipitation. 



As causes of deficient rainfall, Prof. Loomis enumerates 

 five, viz. : (1) a uniform direction of the winds daring the 

 year, such as prevails within the regions of the trades, 

 illustrated by the rainfall of Ascension, Sahara, and South 

 California ; (2) the prevailing wind having crossed a 

 mountain range, thence descends on the leeside, illustrated 

 by desert of Gobi, Chili, and large tracts in Spain ; (3) 

 ranges of mountains so high as to obstruct the free move- 

 ment of the surface-winds towards the interior, as parts 

 of Central Asia and California ; (4) remoteness from the 

 ocean measured in the direction from which the wind 

 proceeds, illustrated by the gradual diminution of the 

 rainfall on advancing eastward into Eutope ; and (5) high 

 latitudes, since beyond lat. 60°, at a little distance from 

 the ocean, it seldom exceeds 10 inches, and there are 

 apparently large tracts in North America and Asia, 

 where the rainfall is less than 10 inches. As regards this 

 last statement, observation scarcely bears it out, since in 

 Europeo-Asiatic continent, only two stations in latitude the 

 above 6o°, viz. Kola in Russian Finland, on the Arctic 

 Sea, and Yakutsk, show rainfalls less than 10 inches, and 

 these are doubtful owing to the short periods over which 

 the observations extend. 



The truth is there are other causes powerfully influencing 

 the distribution of the rainfall than these, which an exa- 

 mination of the rainfall of the individual months, notably 

 January and July, best discloses. These causes have their 

 explanation in the systems of low and high pressures, 

 which appear and disappear with season. Of these the most 



