Book III. OF THE ATMOSPHERE. 365 



3d and 4th, The quadratures, or those aspects of the moon when she is 90 distant from the sun ; or 

 when she is in the middle point of her orbit, between the points of conjunction and opposition, namely, 

 in the first and third quarters. 



5th, The perigee, and 6th, The apogee, or those points of the moon's orbit, in which she is at the least 

 and greatest distance from the earth. 



7th and 8th, The two passages of the moon over the equator, oneof which Toaldocalls the moon's ascend- 

 ing, and the other the moon's descending, equinox ; or the two lunistices, as De la Lande terms them. 



9th, The boreal lunistice, when the moon approaches as near as she can in each lunation (or period 

 between one new moon and another) to our zenith (that point in the horizon which is directly over 

 our heads\ 



10th, The austral lunistice, when she is at the greatest distance from our zenith, for the action of the 

 moon varies greatly according to her obliquity. With these ten points Toaldo compared a table of forty- 

 eight years' observations ; the result is, that the probabilities, that the weather will change at a certain 

 period of the moon, are in the following proportions: New moon, 6 to 1. First quarter, 5 to 2. Full moon, 

 5 to 2. Last quarter, 5 to 4. Perigee, 7 to 1. Apogee, 4 to 1. Ascending equinox, 13 to 4, Northern 

 lunistice, 11 to 4. Descending equinox, 11 to 4. Southern lunistice, 3 to 1. 



2404 That the new moon will bring with it a change of weather is in the doctrine of chances as 6 to 1, 

 Each situation of the moon alters that state of the atmosphere which has been occasioned by the preceding 

 one : and it seldom happens that any change in the weather takes place without a change in the lunar 

 situations. These situations are combmed, on account of the inequality of their revolutions, and the 

 greatest effect is produced by the union of the syzigies, or the conjunction and opposition of a planet with 

 the sun, with the apsides, or points in the orbits of planets, in which they are at the greatest and least 

 distance from the sun or earth. The proportions of their powers to produce variations are as follows : New 

 moon coinciding with the perigee, 33 to 1. Ditto, with the apogee, 7 to 1. Full moon coinciding with the 

 perigee, 10 to 1. Ditto, with the apogee, 8 to 1. The combination of these situations generally occasions 

 storms and tempests : and this perturbing power will always have the greater effect, the nearer these com- 

 bined situations are to the moon's passage over the equator, particularly in the months of March, ai^d 

 September. At the new and full moons, in the months of March and September, and even at the solstices, 

 especially the winter solstice, the atmosphere assumes a certain character, by which it is distinguished for 

 three and sometimes six months. The new moons which produce no change in the weather are those 

 that happen at a distance from the apsides. As it is perfectly true that each situation of the moon alters 

 that state of the atmosphere which has been produced by another, it is also observed, that many 

 situations of the moon are favourable to good and others to bad weather. 



2405. The situations of the moon favour able to bad weather are the perigee, new and full moon, passage 

 of the equator, and the northern lunistice. Those belonging to the former are, the apogee, quadratures, 

 and the southern lunistice. Changes of the weather seldom take place on the very days of the moon's 

 situations, but either precede or follow them. It has been found by observation, that the changes 

 affected by the lunar situations in the six winter months precede, and in the six summer months follow 

 them. 



2406. The octants. Besides the lunar situations to which the above observations refer, attention must 

 be paid also to the fourth day before new and full moon, which days are called the octants. At these times 

 the weather is inclined to changes ; and it may be easily seen, that these will follow at the next lunar 

 situation. Virgil calls this fourth day a very sure prophet. If on that day the horns of the moon are clear 

 and well defined, good weather may be expected ; but if they are dull, and not clearly marked on 

 the edges, it is a sign that bad weather will ensue. When the weather remains unchanged on the fourth, 

 fifth, and sixth day of the moon, we may conjecture that it will continue so till full moon, even sometimes 

 till the next new moon ; and in that case the lunar situations have only a very weak effect. Many 

 observers of nature have also remarked, that the approach of the lunar situations is somewhat critical for 

 the sick. According to Dr. Herschel, the nearer the time of the moon's entrance at full, change, 

 or quarters, is to midnight (that is within two hours before and after midnight), the more fair the weather 

 is in summer, but the nearer to noon the less fair. Also, the moon's entrance, at full, change, or quarters, 

 during six of the afternoon hours, viz. from four to ten, may be followed by fair weather ; but this is 

 mostly dependent on the wind. The same entrance during all the hours after midnight, except the first 

 two, is unfavourable to fair weather ; the like, nearly, may be observed in winter. 



2407. The artificial data are the barometer, hygrometer, rain-gauge, and ther- 

 mometer. 



2408. By means of the barometer, Taylor observes, we are enabled to regain, in some 

 degree at least, that foreknowledge of the weather, which the ancients unquestionably did 

 possess ; though we know not the data on which they founded their conclusions. Chaptal 

 considers that the value of the barometer, as an indicator of the approaching weather, is 

 greater than that of the lunar knowledge of the most experienced countryman, and 

 indeed of all other means put together. {Agriculture appliqme a Chimie, ^c) We shall 

 therefore annex such rules as have hitherto been found most useful in ascertaining the 

 changes of the weather by means of the barometer. 



2409. The rising of the mercury presages, in general, fair weather; and its falling foul 

 weather, as rain, snow, high winds, and storms. 



2410. The sudden falling of the mercury foretells thunder, in very hot weather, especially if the wind 

 is south. 



2411. The rising in winter indicates frost: and in frosty weather, if the mercury falls three or four 

 divisions, there will follow a thaw : but if it rises in a continued frost, snow may be expected. 



2412. When foul weather happens soon after the falling of the mercury it will not be of long duration ; 

 nor are we to expect a continuance of fair weather, when it soon succeeds the rising of the quick- 

 silver. 



2413. If, in foul weather, the mercury rises considerably, and continues rising for two or three days 

 before the foul weather is over, a continuance of fair weather may be expected to follow. 



2414. In fair weather, when the mercury falls much and low, and continues falling for two or three days 

 before rain comes, much wet must be expected, and probably high winds. 



2415. The unsettled motion of the mercury indicates changeable weather. 



2416. Respecting the words engraved on the register plate of the barometer, it may be 

 observed, that their exact correspondence with the state of the weather cannot be strictly 

 relied upon, though they will in general agree with it as to the mercury rising and falling. 

 The engraved words are to be regarded only as indicating probable consequences of the 

 varying pressure of the atmosphere. The barometer, in fact, only shows the pressure of 

 the aerial column ; and the precipitation of rain, or the agitations of the atmosphere are 

 merely events which experience has shown usually to accompany the sinking of the mer- 



