JULY, 1901. MONTHLY WEATHER REVIEW. 316
disturbance of the normal conditions that may have arisen; to compart the conditions of wind and weather prevailing simultaneously at pointr of the sea more or lees remote from each other; to determine the con stant relation, if any, which exists between these conditione; to makt lain the manner in which a vessel, beset by foul winds. might havt
1 een navigated, with the result that these winds would have beer avoided, or even been replaced b fair; and finally to instruct the navi gator as to the conclusions to be &awn from his meteorological obser vations, in order that this result may be accomplished. It was with a view of combining these two equally essential methodr of mefeorological investigations-the old, having for its aim the collec tion of a large number of reliable observations to serve as a basis foi the study of the climatological changes as they occur from month t c month,-and the new, having for its aim the collection of a large num ber ofdaily simultaneous observations to serve as a basis for the studj of the weather changes, as they actually occur from da to day-thal the present form of weather report was adopted. It Amanda hut E
single observation per day, instead of the twelve demanded by the Meteorological Journal, this large reduction being made in the hope that the number of observers would increase in the same ratio as tht services required of them would diminish, a hope which has proveo more than justified. This single observation, however, is to be taker each day over the entire globe at the same instant of time, viz, Greeii wich mean noon. The local or ship's time of the observation will thur varv with the longitude.
!ha &a@ eynoptie weather chrts.-The nest step is the utilization 01
the observations in the construction of the daily synoptic weathei charts. A suitable series of outline charts of the various oceans having beer prepared and dated, one for every day in the year, the observationr contained in the report are plotted, one by one, each in its proper posi. tion upon t h e chart of corresponding date. For this purpose a system symhols is employed which shows at a plance the height of the ba rometer, the direction and force of the wind, the proportion of clouded sky, the nature of the precipitation, whether rain, snow, or hail, the presence of fog, the character of the weather, etc., all precisely as re. corded by the observer, with the exception gf the reading of the ba. rometer, which is first corrected for initial error, and (i f niercurial 1 for temperature. For the North Btlantic Ocean, the first reports tc reach the office, and consequently the first observations to appear upon the chart, are those returned by the westward bound transatlantic liners. These are closely followed by the slower steamships from Europe and the West Indies, and these in turn by the homeward bound sailing vessels. The last reports to appear are those of eastern ARia. These are sometimes as much as a year late in reaching the Hydro. gra hic Office, owing to the practise of holding them until the return of t i e veeeel to the United States. Mastera are therefore earnestly re. quested to avoid this delay by forwarding their observations on reach- ing their first port. The contingent furnished by the sailing vessels is of the highest value, as the observations taken aboard the latter are free from certain constant sources of error introduced by the speed of steam- ships. rta from these various sources accumulate, the plotted ob- servations gcome more and more densely distributed over the chart, each plotting representing the position of an observing vessel at the instant of Greenwich noon and the conditions prevailing in its viciiiity at that instant, until in its final shape the chart for each day offers to view a complete picture of the pressure, wind, and weather covering the entire ocean at the hour and minute of Greenwich mean noon of the day in question. A word as to the value of such a series of charts to the navigator. As is well known, the overning features of the weather in the extra- tropical regions of bot% hemispheres is the practically ceaseless pro- cession of areas of alternately high and low barometer which move around the earth with varying velocity in a general easterly direction, each accom anied by its own system of rinds circulating about the center, the Xirection of the circulation being cyclonic around the area of low barometer, anticyclonic around the area of high. The synoptic charts of the various oceans enable us to follow up the movement of these areas from day to day, to mark the changes which take place in them, and to study the effect of these changes in modifying the weather. It is from this source that the path followed by each of the several barometric depressions that occur during the month, as given on the Pilot Charta of the North Atlantic Ocean, is derived, the aim in thus displaying the daily movement of the storm centers being not on1 that mariners may have at hand the means of ex laining in ac- corzance with the law of storms the occurrence of any [eavy weather encountered, but also that by studying this feature of the Pilot Chart, seeing track after track repeat itself with some slight motlifications, they ma come to know in what part of the ocean to expect tlisturb- ances, wKat will be their character, extent, and duration, and what the direction and velocity of motion of the vortex. It is, however, in the light of the assistance with which careful study of these charts will ultimately furnish the mariner in properly interpret- ing his own isolated observations, that the have their main value. I f
we look through a series of such charta, t i e first impression pained is that they are of endless variety, each one being apparently a law unto
As the re
4 2 4
itself. Close observation, however, will soon reveal certain points of similarity, especially in the position and extent of the arean of high barometer, and consequently in the outflowing winds which surround them, a given distribution of pressure often appearing to hold swap for several days in succession, only to be supplanted by some quite differ- ent but equally persistent arrangement. Careful study has thus shown that the daily synoptic weather charta of the North Atlantic Ocean may, with certain restrictions, all be referred to one or another of a limited number of types, each type possessing certain characteristic features, which vary from season to season, and each exhibiting a certain degree of persistenc It is u n tge study of these &pea of weather, their character dura- tion, anrorder of succession, that the hope of eventua!l prehicting the weather over the ocean several days in advance rests. guch a studp demands that the meteorologist have at hand a series of daily sTnoptic charts. accurate in every respect, and covering the ocean, especially in the higher latitudes, as widely and as completely as possible, and it is to the merchant marine that he must look for the material necessary for the construction of these charts. Once having attained a knowledge of these typea. moreover, the ability of the mariner to forecast the weather from his own isolated observations would be vastly increased. Knowing the type of weather prevailing, his observations of pressure, temperature, winds, and clouds, would gain a new importance, show- ing whether the type was about to change, and in what direction. The tabubth of t?u obwmxatione.-Having served their purpose in the construction of the daily synoptic charta, the observations are read for tabulation. For this purpose the surface of the ocean is suppose$ to he divided into a number of fields or squares, bounded by the even 5O parallels of latitude and meridians of longitude, OD, 5, loo, 15O, etc. The observations are tben separated according to months, and all of those within a given square and during a given month (irrespective of the year) are assembled. The next step is to obtain for each month and each s uare the average temperature of the surface of the sea, the ratio that %e winds from each compass point bear to the total number of winds, the average force of the winds, the frequency of the various forms of clouds, varieties of weather and character of the sea, and the average velocity and set of the current. These final values are then carefully tabulated and map d. and the results given to the seafaring community in the shape of g e Monthly Pilot Charta published by the
Hydrographic O5ce.
LUNAR INFLUENUES IN METEIOROLOC+Y.
The admirable elementary treatise on meteorology by Prof.
Alfred Angot of the Central Meteorological Bureau in Paris,
published in 1899, concludes with a chapter on the prediction
of the weather and the regular periodicities that have been
sought for i n meteorology. After showing that long-range
predictions can not yet be made by utilizing any such periods,
and that even the sun spots have not yet been shown to have
any special influence. Angot adds a paragraphs with refer- ence to the lunar periods, which we translate as follows:
The idea that the moon exerts any influence on meteorological phe- nomena goes back to the most ancient times; there is no belief that has left more traces in the popular traditions in regard to the weather, nor that has been the subject of more controversy. Let us recall that the time occupied by a true or sideral revolution of the moon is 27d. 7h.43m, or 27.322 days; the apparent or synodic period, after which the sun, earth, and moon return to their same re- spective positions, isa little longer, vie, Bd. 12h. 44m., or 29.531 days, it is after this latter interval that the phM8of the moon again become the same. The anomalous v m l u t h or mean value of the intervals of time separating two consecutive passages of the moon through its shortest distance from the earth, is 27d. 13h. lQm., or 27.555 days. Finally the orbit of the moon has a mean inclination to the ecliptic of
6O 8/ 4W'; the maximum declination of the moon. therefore, varies between 18' 10' and 2 8 O 45/, while the maximum declination of the
BUU is 28' %I.
The moon imparts tous only a very small proportion of the light and heat that she receives from the sun; the heat that she sends toward the earth is so feeble that the most powerful instruments and the most delicate methods of measurement must be employed to discover it; there can, therefore, not be any question of a luminous action of the moon and much lees of a caloric action, and we can scarcely think of snything else but an attractinn analogous to that produced by the tides on the great masses of water of the oceans. It is, therefore, neceesary to first seek to discover whether the action of the moon does produce ktmospheric tides that show themselves by the periodic variations in the height of the barometer. If we observe the pressure at the lunar hours, that is to say, when the moon passes the meridian, and she is distant from it 16O, 30°, Go, $tc., and if we take hour1 means of the values observed during a very long period of time, in oriel to eliminate the disturbances, these means
316 MONTHLY WEATHER REVIEW. Jum, 1901
will certain1 give an indication of a lunar tide, but extremely feeble; it will on1 {e found at the equatorial stations and disappears entirely in the miIdle latitudes. At Batavia the maximum pressure occurs a half-hour or an hour after the upper and lower passages of the moon over the meridian; the minimum occurs from six to seven lunar hours after the maximum; the total estent of the variation is only 0.11 milli- meter, which corresponds to a column of water of about 1.5 millime- ter [or one seven-thousandth part of the standard average atmospheric pressure.-E~.] The insignificance of the diurnal lunar variation of pressure indi- cates that this must also be true of the variation corresponding to the revolution of the moon aroiind the earth, that is to say, to the phases of the moon. I n Batavia the pressure is the feeblest at the tlnie of new moon and most powerful shortly after the period of full moon; the total estent of this oscillation does not reach 0 2 millimeter. The diurnal rotation and the synodic revolrition of the moon therefore cause tides in the atmosphere as well as in the oceans, but the atmos- pheric tides are so extremely feehle that they scarcely esceerl the limit of accuracy of tlie barometric ohserrations. The study of the influence of the synodic revolution, or of the phases of the moon, upon other nieteorological phenomena produces results which are absolutely contrailictciry. and which have been discussed in detail by Arago and, more recently. hy Van Bebber. We shall, there- fore, limit ourselves to summarizing briefly the conclusions arrived at by them. The temperature, the cloudiness, and storms clo not show any pe- riodicity in relation to that of the phases of the moon. In Germany north and northeast winds seem most freqiient in t h e period of the last quarter of the moon nnd most rare in the first quarter; the south- west winds show an inverse variation. But this law has not been verified in any other countries. At Paris and in Germany the niasimum numher of rainy days occurs between the first quarter and the full moon: the minimum number between the last quarter and the new moon. The relation of the maxi- mum to the minimnm is 1.26 at Paris and 1.21 in Germany. It would, therefore, at first sight seem that there is here a true law and that the prospects for rain are greater by a fourth or a fifth after the first quar- ter than after the last. But even this would be too sliglit a difference to be made use of for a serious forecast. Besides, this law aloes not hold good for the south of France. At Orange, for example, the mini- mum of days with rain occurs between the full moon and the last quar- ter and at Montpellier in the first quarter. If there is any relation between the phases of the moon and the rainfall, this relation is, therefore, very complex and variable from one region to another. The study of the changes of the weather lias produced still less con- vincing results. I n discussing the observations made at Padua in the last century, Tosldo found that, according to the popular belief, the weather is much more variable at the time of new moon than at the other lunar periods. But convinced in advance of the existence of the influence that he wished to demonstrate, Toaldo attributed to the action of the new moon the changes in the weather occurring one or two days either before or after; whereas for the rest of the lunar pe- riod each day was considered separately. If now rigorous computa- tions be made, giving to each day the same value, there will no longer be found any trace of the influence of the phases of the moon on the changes of the weather. During the past few years the study of the influence of the moon has been again taken up in a manner ap arently more ecientific. I n the first place, all idea has been abanzned of finding any relations between the meteorological phenomena and the phases of the moon; that is to say, the synodic revolution which rep- resents only the relative positions of the earth, the moon, and the sun. Then the anomalistic revolution was studied, which corresponds better to the respective real positionsof the earth and the moon. But, above all, the position of the moon in declination has been compared, not with any special local meteorological phenomenon, such as tempera- ture, rainfall, changes of the weather, etc., hut with the distribution of preseure over the surface of the globe asa whole. The fundamental idea of these researches is that the movements of the moon in declina- tion may lead to general displacements of the air, or a balancing be- tween the tropical regions and the higher latitudes, and thus cause periodical changes, such, for example, as in the boundary of the trade winds and in the law of change of pressure with latitude. We should then understand that a movement of a zone of high pressures, for ex- ample, might cause fine weather on one side of the zone and at the same time foul weather on the other side, and that these variations, which at first sight seem contradictory, might nevertheless be due to one and the same cause. These studies are, however, of too recent date and still too undeveloped to have already given results that may be considered as sufficiently conclusive and general. It is, however, interesting to mention them here, since b j continuing to work in the same lines we may, perhaps, succeed in discovering the true relations between the moon and the henomena of the weather, since the earlier researches have not brouggt about any positive conclusion. On the whole, in the present state of our knowledge, it can not be affirmed that the moon does exert any influence upon the weather, but at the same time i t should not be denied that this influence may possibl exist. I n any w e , it would show itself by complex phenomena, sucg
as the displacement of the zones of high and low pressure, and might cause very different results in different regions. I n concluding the examination of the various opinions in regard to the influence of the moon, it may be well to say a word on the opinions concerning the lrins roua8ps. OT aarml moon. This name has been given to the lunar period which, beginning in April, has ita full moon either in the second half of that month or in the month of May; if there are two new moons in April it is with the second that the harvest moon begins. Agriculturists declare that often at that time, when the sky is clear and the moon shines brightly during the night, the tender buds are frozen and turn red even although the temperature of the air does not fall below freezing; nothing of this nature occurs if the moon re- mains hidden behind the clouds. The explanation of this phenomena is very simple and the moon has no part in it. When the sky is clear and the atmosphere dry and transparent (this is the time when the moon shines most brightly) the temperature of the bodies subjected to the nocturnal radiation falls far below the temperature of the air. If, during the clay, the temperature has not been very hi h the nocturnal radiation may then chill the plants below freezing anfthey will freeze although the air remain at n higher temperature; on the other hand the plants will not be frozen if there are clouds to diminish the radia- tion. The conditions that lead to these freezings are therefore a clear sky and a relatively low temperature during the day. At the end of May or June the mean temperature is generally too high to allow us to fear these freezes although they do occur sometimes. Before the com- mencement of the harvest moon, that is to say, at the end of March or the beginning of April, the temperature is lower than during the har- vest moon itself; the conditions are therefore much more favorable for freezing by radiation; but as the vegetation has not yet begun these freezes do not cause any damage and do not attract any attention. We have here to do with a very simple phenomenon in which the moon plays no other part than merely to indicate by its brilliancy when the sky is pure and transparent. In the countries in the south of France, where the vegetation is more advanced than in the center and the north, the critical eriod of vege- tation is no longer during the harvest moon but during tie lunarperiod which precedes it.
_- --- __
"HE RED DUST OF MARCH, lQOl.
In connection with the remarkable dust storm that pre-
vailed over a large part of Europe between the 10th and 13th
of March, Monsieur M. Barac, director of the petroleum re-
finery at Fiume has made an examination of the dust and we
quote the following from his report. The chemical analysis of the dust gave the following re-
rults :
Per cent.
Silicic acid (Si 0,) ............................ 49.49
Oxide of iron (Fe, Os). ...................... 9.96 Clay (AI, 0,) ................................. 12.10
1.99 Oxide of calcium (Ca 0). ..................... 11.46
0.40
Carbonic acid (C02).. ....................... 8.96
Organic substance.. ......................... 6.48
Traces of sodium, sulphuric acid, hydrochloric acid and loss.. ............................. 0.16
Oxide of manganese (Mn, O,).. ...............
Oxide of magnesium (Mg 0). .................
Total .................................. 100.00
The micrascopic examination, under a power of 640, shows that the mass was composed principally of colorless, mixed
with a small portion of colored, irregular fragments of crys-
tals and particles of minerals together with the skeletons of
micro-organisms and small particles of soot. Small quanti-
ties of well-formed, sharp-edged rhombohedric carbonate of
lime, quartz prisms, and cubes of chloride of sodium, and the
lime as well as the quartz crystals showed the phenomena of
chromatic polarisation.
.In regard to the diameters of the particles, the smallest were 0.001 millimeter, the average 0.017 millimeter, while
the maximum size of the fragments of crystals was 0.051 mil-
limeter, and that of the structureless mineral particles 0.113 millimeter.
If we compare these results with those published by A. E.
Nordenskiold, Zeit. Oest. Gesell. fiir Meteorologie, relative to
the dust that fell May 30, 1892, in Sweden, we are led to con-
clude that the dust of 1901 belongs to the mme class as the