mulative effect of the moon's attraction with the daily wave of rotation, and the resistance of the æther. One peculiarity of this lunar-aerial wave deserves notice for the indirect confirmation that it lends to the rotation theory of the daily aerobaric tides, and the evidence it furnishes of opposite tidal effects, which require consideration in all investigations of this character. When the daily lunar tides are highest their pressure is greatest, the lunar influence accumulating the air directly under the meridian, so as to more than compensate for the diminished weight consequent upon its "lift." But in the general aerial fluctuations, as we have seen, and also in the weekly tides, a high wave is shown by a low barometer, and vice versa. The daily blending of heavy and light waves produces oscillations, which are indicated by the alternate rise and fall of the barometer and thermometer at intervals of two or three days. Mr. Flaugergues's observations at perigee and apogee seem to show that a portion of the movement of the air by the moon is a true lift, which, like the lift of rotation, must probably exert an influence on the thermometer as well as on the barometer. On comparing the daily averages at each of the quadratures and syzygies, I found the difference of temperature too slight to warrant any satisfactory inference; but a similar comparison of the hourly averages, at hours when the sun is below the horizon, gave such results as I anticipated, as will be seen by a reference to the following Table of barometric and thermometric means at the moon's changes. In obtaining the above averages I was obliged to interpolate for such changes as took place on Sundays or holidays, when no observations were taken. The interpolation, however, does not affect the general result; and, on some accounts, the table is more satisfactory than if the observations had been made with special reference to a determination of the lunar influences, accompanied as such a reference would very likely have been, by a bias to some particular theory. The thermometric and barometric averages show a general correspondence in the times of the monthly maxima and minima, the correspondence being most marked and uniform at midnight, when the air is most removed from the direct heat of the sun, and we might therefore reasonably expect to find the clearest evidences of the relation of temperature to lunar attraction. By taking the difference between the successive weekly tides, we readily obtain the amount of barometric effect in each quarter. The average effect is more than three times as great in the second and third quarters, as in the remaining half month,—a fact which suggests interesting inquiries as to the amount of influence attributable to varying centrifugal force, solar conjunction, or opposition, temperature, &c. Although, as in the ocean tides, there are two simultaneous corresponding waves on opposite sides of the earth, these waves are not of equal magnitude, the barometer being uniformly higher when the moon is on the inferior meridian, and its attraction is therefore exerted in the same direction as the earth's, than when it is on the superior meridian, and the two attractions are opposed to each other. I find, therefore, marked evidences of the same lunar action on the atmosphere as on the ocean,-the combination of its attraction with that of the sun producing, both in the air and water, spring tides at the syzygies, and neap tides at the quadratures; and I believe that the most important normal atmospheric changes may be explained by the following theory: The attraction and rotation-waves, as will be readily seen, have generally opposite values, the luni-solar wave being Descending, from 0° to 90°, and from 180° to 270°. Ascending, from 330° to 60°, and 150° to 240°. From 60° to 90°, and 240° to 270°, both waves are descending while from 150° to 180°, and 330° to 360°, both are ascending. In consequence of this change of values, besides the principal lunar maxima and minima at the syzygies and quadratures, there should be secondary maxima and minima at 60° in advance of those points. The confirmation of these theoretical inferences by the St, Helena observations appears to me to be quite as remarkable as that of my primary hypothesis. If we arrange those obser vations in accordance with the moon's position, and take the average daily height of the barometer, we obtain the following ⚫ Counting from either syzygy. 1. That the average of the three years corresponds precisely with the theory, except in the secondary maximum, which was one day late. 2. That the primary maximum occured at the quadratures in 1845 and 1846, and one day before the quadratures in 1844. 3. That the primary minimum occurred at the syzygies in 1844 and 1845, and one day after the syzygies in 1846. 4. That 1846 was a disturbed year; and, if it were omitted from the table, each of the remaining years, as well as the average, would exhibit an entire correspondence with theory, except in the primary maximum of 1844. 5. That 1845 was a normal year, the primary and secondary maxima and minima all corresponding with theory both in position and relative value. 6. That the deviations from perfect correspondence with theory can be easily explained by the relative positions of the two aerial ellipsoids of rotation and attraction. 7. That the tertiary maxima and minima, or the turning-points between the primary and secondary maxima and minima, are less stable than the primaries and secondaries. At extra-tropical stations I should look for important modifications of the theoretical results, some of which I propose to explain hereafter. În a former communication on the rotation-tide, I stated that "the law of tidal variation, derived from an exclusive reference of the aerial motions to a supposed stationary earth, is precisely *Counting from either syzygy. Since the tabular numbers represent the semi-ares of the barometric curve, and not the simple ordinates, the values for 0° and 180° are the same. the same as the law that is derived from the consideration of the relative attraction of the two bodies revolving about their common centre of gravity." That such would be the case might have been reasonably expected from the dependent connection of rotation and revolution with gravity. I was therefore led to believe that the daily lunar tides might be indicated by the same expression as the weekly lunar and daily rotation tides. On investigation, I find that such is indeed the case. If M is the barometric mean for any given day and place, and is the moon's altitude, the lunar tide may be expressed by MC (sin cos), C being a constant to be determined for each station. The rationale of Mr. Flaugergues's second and third inferences thus becomes evident; the phenomena of ocean tides are connected with those of the air, which, being subject to fewer extraneous disturbing influences, can therefore be more easily investigated; and the long-suspected obedience of the principal meteorological changes to fixed mathematical laws is at length demonstrated. ART. XXVI.-Extracts from the Address of Dr. J. W. Dawson, President of the Natural History Society of Montreal, at its annual meeting, May 18, 1864.' Fossils of the Laurentian. By far the most important publication of the past year, in the Natural History of Canada, has been the great Report of the Geological Survey, a work in which, as the achievement of members of this Society, we may very well take pride; and on which we may congratulate ourselves as facilitating the labors. of those among us who pay attention to geology, either with a view to practical or scientific results, and as greatly raising the scientific reputation of this country. The Report of the Survey has already been reviewed in the Naturalist, and I propose here, not so much to say anything as to its general merits, as to refer to a few points in Canadian geology to which it directs our attention. One of these is the discovery of fossils in the old Laurentian rocks, heretofore usually named Azoic, as being destitute of life, and much older than any rocks known to contain fossils. The oldest remains of living beings, until this discovery, had been found in rocks known as Cambrian, or Primordial, and equivalent in age to our oldest Silurian of Canada, or at the most to our Huronian. But the Huronian series in Canada rests on the 1 From the Canadian Naturalist, 1864. upturned edges of the Laurentian, which had been hardened and altered before the Huronian series was deposited. Again, Sir William Logan has shown that the Laurentian system itself contains two distinct series of beds, the upper of which rests unconformably on the lower. There are thus in Canada at least two great series of rocks, of such thickness as to indicate two distinct periods, each of vast length, below the lowest fossiliferous rocks of other countries. Yet, in the lowest of these so-called Azoic groups, fossils have now been found; Canada thus far distancing all other parts of the world, so far as yet known, in the antiquity of its oldest fossils. I have had the happiness to submit these remarkable specimens to microscopic examination, at the request of Sir W. E. Logan, and have arrived at the conclusion that they are of animal nature, and belong to the very humblest type of animal existence known, that of the Rhizopods, though they far outstrip in magnitude any known modern representation of that group. The discovery of this remarkable fossil, to be known as the Eozoon Canadense, will be one of the brightest gems in the scientific crown of the Geological Survey of Canada. In connection with this subject, it is to be observed that the grand order of succession in the older number of the Laurentian system of rocks seems to be the same with that so often represented in other parts of the geological scale. First, a coarse fragmentary series, represented by conglomerate and gneiss; next, a calcareous and fossiliferous band, represented by the Eozoön limestones; next, a finer earthy series, represented by dioritic rocks. This brings the Laurentian into a cycle somewhat similar to that of the Potsdam sandstone, the Chazy and Trenton limestone, and the Utica slate and Hudson river in the Lower Silurian; or to that of the Medina sandstone, the Niagara limestone, and Lower Helderberg in the Upper Silurian; or to that of the Oriskany sandstone, Corniferous limestone, and Hamilton and Chemung groups in the Devonian; or to that of the Lower Carboniferous conglomerates and sandstones, the Carboniferous limestones, and the Coal measures in the Carboniferous period. This recurrence of cycles of deposit cannot be accidental. It is more or less to be seen throughout the geological scale, and in all countries; and, as I have elsewhere pointed out, it includes numerous subordinate cycles within the same formation, as in the coal measures. Eaton, Hunt, and Dana have called attention to it; but it deserves a more careful study as a means of settling the sequence of oscillations of land and water in connection with the succession of life. It will also be important in giving fixity to our geological classifications, and may eventually aid in establishing more precise views of the dynamics of geology and of the lapse of geological time. The progress of the |
