now so opportunely raises in his letter. Whatever my opinions may have been, I have referred cyclones to causes but vaguely hinted at. I have now to explain my views more clearly with regard to both cyclones and the barometer. It has appeared to me that we may reasonably evade the difficulties which beset the barometer from its "uncertainties," if we consider weather as proceeding from two causes, viz., primary and secondary. The primary cause of all weather change is undoubtedly electricity; but in a limited sense, and for practical uses, I purpose in future to distinguish the electric or primary from what we may call the mechanical or secondary effects: by so doing we approach what may truly be called a weather system. Now we are in possession of the facts of the greatest importance in our investigation, viz.,— 1st. The heaviest hurricanes which sweep our globe do cause & great disturbance of the barometer. 2nd. Exceedingly heavy gales do occur which scarcely disturb the barometer. J We call the first by various names, such as hurricanes, cyclones, &c., and, as I stated in the Nautical in 1852, they invariably originate in the region of equinoctial calms; (the cause which produces them is quite another subject;) they move along with differing velocities, and at first stride the earth on or close to a neutral magnetic line, which we call the "line of no variation:"-they gradually diverge from the neighbourhood of the equator until having reached near to the polar limit of the region of the Trades, they recurve towards the ncarest pole, again drive along upon some one line of equal magnetic variation until they lose themselves in high latitudes or disperse altogether. These cyclones, having a distinctly traced whirling motion, the air surrounding them soon partakes of such gyrations; and precisely as we see in a small whirlpool, (we often see it in our teacup,) centrifugal force removes a portion of the fluid from the centre of the whirl, and in the case of the cyclone, consequently relieves the surface of the mercury, which is open to the atmosphere in the barometer, from some of its pressure; in other words, the mercury is no longer sustained so high in the vacuum end of the tube, and the barometer "falls." Now I call this species of storms mechanical, because the motions of the air and mercury follow, upon a very large scale, the common laws of gravity which affect all other ponderable bodies. As regards the second class of gales which scarcely (or sometimes do not) disturb the barometer, I place them under the category of lunar equinoctials, for the following reasons. Attributing all changes of weather to electric influences, we have in the electric fluid an imponderable body. Its free permeation of the atmosphere does not therefore affect the density of the air except with minor operations, which disturb temperature, and by resulting condensations and evapo rations (the means by which in this class disturbance of weather is produced) cause displacement of air, when such does occur, on a comparatively small scale, occasioning the depressions or risings which we frequently but not uniformly see in the barometer. We cannot esti mate by weight the presence of electricity in a fluid or solid, therefore an accumulation of electricity cannot by its presence affect the weight of the atmosphere nor, therefore, disturb the barometer. Hence, I say, we have storms which do affect it, and storms which do not affect it. Now, without my lunar theory mankind have positively no means from which to take "warning" when storms of the latter description are to be looked for. That these are not unfrequent I at once demonstrate even from the last month (July). On the 18th, a very heavy gale from S.W., having (according to the register of the Royal Exchange anemometer) a velocity of upwards of fifty miles an hour, sprung up while the barometer was above Belleville's average height for the date, and the barometer had been either steady or rising for the sixty previous hours! Thus we had no warning whatever of any danger. The "heavy gale," therefore, was no cyclone, because it did not affect the barometer. What then was it? according to my arrangement, as explained above, it must have been of the primary or electric order and if so, it could only have happened at the time of lunar equinox or stitial colure. Now, if you will refer to my prediction for this date, you will see that I did predict it, because the moon was at the stitial colure on the 18th at midnight, as I forewarned weeks beforchand (I could give other instances from the same month.) On the other hand, to show that great indications in the barometer are sometimes without any perceptible consequences, let me state that during the 1st, 2nd, 3rd, and 4th of July last, (in the same month,) there occurred a great and determined fall of the barometer, until it reached from 30.25 inches to 29:39. Admiral Fitz Roy even sent a telegraphic warning to the coast, her Majesty's ships sent down topgallant masts and prepared for the expected storm,-but it did not come. We had a moderate single reefed topsail breeze at 5h. p.m., which died away towards 7h. p.m., when rain set in. The lunar colure happened on the 5th at midnight, and we had a few hurried squalls during the day, but they did not affect the barometer in the least. : Having thus incontrovertibly shown that I have solid grounds for my assumptions, or, rather, shown your readers by one example how I could prove my position, if called upon,--I will trace onward the subject of cyclones as connected with the lunar theory. I say incontrovertibly, because I rest upon easily attested facts, corroborated by extensive observations. So entirely new a system of weather study suggests a wide field for further scrutiny. It presents all our collected registrations and records in a new focus. I confess my inability to have done more from want of access to such collections, or, indeed, to any public records. The delay, however, has had its advantages, inasmuch as my own personal watchings were made with the more care and regularity. Your Mauritius correspondent is in a position somewhat peculiar as compared with ourselves, and without having his attention properly NO. 9.-VOL. XXX. 3 R drawn to one circumstance might suspect the accuracy of my second assumption (as regards some gales not disturbing the barometer), because he would naturally appeal to his registrations made at Mauritius. If, however, he read my letter in the Nautical for February last, he will see that the region of the Trades should be exempt from the general primary or electric operations of the lunar theory, inasmuch as disturbances of weather at the Mauritius at the periods of lunar equinoxes or lunar stitial colures would not occur there, from its being situated in the Trades; and therefore, being subject only to one species of disturbance,-viz., the secondary or mechanical, which always affects the barometer, he will not be in a position to corroborate my assertions as to disturbances of other kinds. He has kindly furnished us with information as to past weather, on which I have the pleasure of offering a few remarks. That which I am so often obliged to speak of as "my lunar theory" relates to atmospheric disturbances, which (I am also obliged to repeat) occur at the periods of the moon's crossing the earth's equator, and of her being at her "stitial colure." Dropping for the moment the two limited and subordinate divisions of primary and secondary, which I have only adopted for illustration and distinction, I believe that the interruptions of the great electric currents of the globe thus caused by her change of position affect both hemispheres alike, and are the sources of all changes of weather whatsoever. I expected to find it so before my suspicions were confirmed by actual observations by one of my sons in Tasmania. Accordingly, cyclones, as well as all other disturbances upon a grand scale, would, if belonging to my system at all, derive their origin at these periods only. It therefore is important to examine records of cyclones, noting their localities in particular, in order to arrive at proofs of this. Their rate of travelling, too, should, when practicable, be ascertained, in order to estimate the number of days which might have passed since they were called into being, for your readers will remember my having called attention to the circumstance of our heaviest gales usually occurring two or three days after the lunar equinox or stitial colure. Now, if my suspicions as to the origin, date, and birth-place of cyclones be accurate, those which reach us must have originated not far south-eastward of the West India Islands; and therefore must, before visiting us, have travelled along a well known curving track of some 4,500 miles. Bearing in mind that if they were formed at a lunar period referred to, this 4,500 miles could not possibly be traversed in two or three days, it is most probable that at least one lunar period (of about seven days) intervened; and this is likely, because if they take nine to twelve days to reach us (which this hypothesis would show), their velocity of travel would be variable from 300 to 500 miles a day, and this is very near the general supposition, from observation. In order that I may here, too, show that I am treading on some solid grounds, I take the past year, 1860, and note the dates of all the gales which happened in that year attended with great barometric or marked depressions, such as I venture to affirm indicate a cyclone. The gales of January 3rd, 30th, February 6th, March 3rd, May 2nd, would have happened about nine days after a lunar period. That of January 21st nine days and a half after. Those of March 31st, September 24th, and the Royal Charter gale of October, 1859, ten days after. Those of February 19th and 27th, and May 26th, eleven days after. Those of 2nd June and the St. Kilda gale of 3rd October, twelve days after. We will now examine the Port Louis records, as kindly given by your Mauritius correspondent in your last July number, remembering that in this instance the nearer the time of the occurrence of cyclones approaches to the dates against which I have given warning, the nearer the cyclone itself ought to be found to the cradle of its birth, viz., the region of equatorial calm. We are told that on 1860.-December 5th.-" There was a cyclone in 8° S. and 80° E.” N.B. This is within the region of equinoctial calms, and 26th." The barometer commenced falling, and continued doing of the 14th, 15th, and 16th in 94° E. may have originated at the lunar equinox of the 11th. 19th to 21st." On 19th, 20th, and 21st, there was another considerable fall in the barometer." N.B.-Here the fall commenced on the day of lunar stitial colure. April 3rd to 7th.-" A cyclone raged during this time in 14° S. and 76° E." N.B.-This, if formed at the period of lunar stitial colure on the 31st March, would have travelled about 700 miles in three days. It was evidently travelling very slowly from its duration in the neighbourhood of 14° S. 11th to 14th." The barometer fell gradually, showing a disturbance in the S.E. Trades." N.B.-Probably a passing cyclone which originated on the 7th, the day of lunar equinox. The above may be taken rather as the manner in which I should treat observations on cyclones than as an attempt to prove anything, although it is highly encouraging. Having at first said so much in partial depreciation of the barometer, I feel bound to state that since we find that the heaviest gales are those which alone can be detected in the steady fall of the mer cury some time before their arrival, the warnings we occasionally receive from Admiral FitzRoy are worthy every attention along the coast, because I believe that great falls never occur from any cause but approaching cyclones; and while we laugh at the occasional fruitlessness of some warnings, and rejoice to have escaped the storm that threatened, let us be thankful for the vigilance which tried to give us the timely warning. LUNAR EQUINOCTIALS,—or, the Past and Future. I have trespassed so much on your space that I will only, as regards the Past, state that June 21st--Produced very destructive floods (in Yorkshire, &c.) 28th-Was marked by change of wind and very disturbed wea ther. July 5th or 6th-Hard squalls and occasional rain. 12th.-Change of wind from S.W. to E.S.E., and much thunder and lightning. 18th or 19th.-Heavy gale S.W. 25th.-Heavy gale S.W. August 2nd.-Heavy gale 2nd p.m. till 3rd a.m., S. W. to West. 8th or 9th.-Fresh gale W.S. W., W.N.W., and W.S.W. 15th. Great change from pleasant summer calm of previous days to windy, gloomy W.S.W. weather. The Future. August 15th-22nd-29th or 30th September 5th-11th-18th-25th or 26th |