from E.S.E.; and there is little doubt that the centre of a second cyclone was in about 15° S. and 63° E. On the 10th, the Futta Salam, in 16° 26' S. and 73° 58′ E., had fresh breezes from South,-bar. 29.85; the Meteor, in about 13° 10′ S. and 78° 52' E., a hurricane from S.S.W.,-bar. 29.10; and the George and Juliette, Captain Fabre, in 12° 34' S. and 88° 40' E. (Paris), strong winds from West. The same signs of a second cyclone to the northward of Rodriguez still exist. On the 11th we have exactly the same evidence of both cyclones; but the Trade-wind to the southward of Rodriguez has much increased in strength. On the 12th the evidence is most satisfactory. The centres of the two cyclones are about 1,200 miles apart. The following vessels are in the easternmost,-Meteor, in about 13° 31′ S. and 79° 44′ E., with strong gales from W.S.W.,-bar. 29.50; Bussorah Merchant, Captain Delange, in 9° 53′ S. and 81° 30′ E., with strong winds and very heavy squalls from West, and a very heavy sea,-bar. 29.88; George and Juliette, in 14° 18′ S. and 87° 36′ E. (Paris), with fresh winds from N.N.W. and a very heavy sea from W.N.W. The westernmost cyclone had its centre in about 18° 15′ S. and 60° 40′ E., as shown by the logs of many vessels. On the 13th, 14th, 15th, and 16th the evidence of the existence of both storms is complete; but the second (the Mauritius one) is alone found on the 17th. The courses of those two storms have not yet been traced with sufficient accuracy; but it is plain that the Mauritius one passed the island to the northward and westward, impinging upon Reunion, the high land of which seems to have for a time affected its form and intensity. From noon of the 12th to noon of the 13th it travelled at the average rate of five to six miles per hour, and for the next two or three days remained nearly stationary, but oscillating backwards and forwards, as if preparing to set off afresh. This accounts for the constancy of the wind and the state of the barometer at Port Louis. The brig Wild Wave, Captain Maughan, at noon of the 12th, in 18° 48′ S. and 61° 51' E. (by account), had a severe gale from S.b. W., with the barometer at 29.52. She was kept right before the wind, her commander, who knew the nature of the storm, being anxious to get to its northern side without delay. During the next four hours (the vessel running at the rate of seven knots) the wind veered to S.S.W., S.W., and West. At 5h. p.m. she was hove to under bare poles, Captain Maughan expecting that the storm would travel away from him. The barometer, however, kept falling, the wind hauling to northward, and the vessel drifting at the rate of two knots per hour. At 8h. a.m. of the 13th the wind was easterly (bar. 28.60) and at noon from the southward of East (bar. 28-40). The wind then died away nearly all at once (lat., D.R., 18° 58' S., long., D.R., 57° 22′ E.), and a calm of fifteen hours' duration succeeded. At 3h. a.m. of the 14th (bar. 28-40) the breeze suddenly freshened from South and East, and at 8h. it was blowing a hurricane from S.W. At 9h. 30m. the vessel was got before it again (bar. 28-65). At 10h. the wind was West (bar. 28.65). At noon it was W.N.W. (lat., D.R., 18° 30′ S., long., D.R., 57° 30′ E.) It then hauled to the northward, and at 5h. p.m. the ship was hove to on the port tack, the wind decreasing and hauling to the eastward of North. The centre of the storm at noon of the 15th was about ninety miles N.E.b.N. of Port Louis; and at noon of the 16th about fifty miles N.W. of it. On the 17th, at noon, it was about seventy miles to the S.S.E. of St. Denis; but on that day it was probably disturbed and flattened by the land. At noon of the 18th it was in 24° 15′ S. and 56° 30′ E. Its shortest distance from St. Denis was about fifty miles, and from St. Rose about twenty-five miles. But more data are required. On Tuesday, the 26th of February, the barometer began to go down again, with light S.E. winds, and continued to fall very slowly but sensibly on the 27th and 28th, the weather being fine. There was no doubt that another hurricane was commencing to the eastward and northward of the island, although the statement was received with derision. On the 1st of March the weather was still fine, but the barometer descending, though it stood, at 9h. 30m. a.m., at 29·966. It had previously been announced that bad weather existed to the eastward and northward, and on this day it was added that there were signs of a hurricane in about 15° S. and 60° to 75° E. The barometer continued falling, though it was still high, being, at 9h. 30m. p.m., at 29.986. On Saturday, the 2nd, it began to fall more rapidly, the wind increasing from S.E., with an ugly appearance. The following table is compiled from the hourly observations which were taken :— February 27th 30.076 30 102 30.010 30.080 30.014 29.928 29.984 29.852 29.664 29.550 29.540 29.688 The wind increased from S.S.E. to South, and blew very hard. At 8h. p.m. of the 2nd it was from South, blowing hard, with furious gusts and rain. It then veered gradually to S. W., with furious squalls and rain, and began to moderate at midnight. At 10h. a.m. of the 3rd it was from West in strong steady breezes. The total fall of rain during this gale was only 1.582 inches. The anemometer already alluded to (Osler's anemometer here was blown down in the former gale) is said to have indicated a pressure of 30lbs. per square foot, which must be nearly correct. This year, as well as 1860, has hitherto been remarkable for rain and hurricanes in the Southern Indian Ocean; and it is interesting to know that in the Northern Hemisphere there have been at the same time rigid winters, as if the whole atmosphere were affected by some general cause. Have the rigid winters of the North of Europe and the hurricanes of the Indian Ocean a periodicity?-and if so, what connection has it with the sun? C. MELDRUM. ON THE DEFECTIVE EXPLANATION AS GIVEN IN THE NAUTICAL ALMANAC FOR 1864. By James Gordon, M.A. In my first paper, published in the Nautical Magazine for July last, I referred to the Nautical Almanac for 1861. I now beg to call the attention of nautical men to an important alteration which has been made regarding the Diff. for 1 hour of the sun's declination and equation of time. I have before me the Nautical Almanacs for 1861 and 1864. In 1861 these hourly differences were found by dividing the daily difference by 24, but in 1864 they are not. On looking at the explanation of page I. N.A., precisely the same words are used both for 1861 and 1864 regarding the diff. for 1 hour of the declination: consequently nautical men will, to a certainty, calculate the declination as formerly, and thus produce a greater error than by the usual method. Example. Required the sun's declination for 1864, December 19d. 21h. 54m. Greenwich apparent time. 1st.-Correctly computed by second differences. Declination. 1st diff. 20 23 27 1 .5 Dec. 19 2nd diff. 21h. 54m. n = 0.9, n. 2nd.-Computed by hourly diff. for 1864. Dec. 19 gives...... 23°26′ 17′′-8 Corr. for 21-6h..... +52 1 Declination by method of 1864. 23 27 9-9 Diff. 2'41 21.6 1446 241 482 52.056 3rd-Computed by hourly diff. as found in 1861. Consequently by the new method the error is 11"5, by the usual way it is 13. Remark. It is therefore of importance to inquire how the diff. for 1 hour is obtained, and how it is to be used. In 1864 it is obtained for any given day by dividing the change of the declination (page I.) between the day before and the day after the given day by 48. Thus, to find it for 1864, Dec. 19. To use such hourly differences instead of using the diff. opposite any given day, we must compute the diff. for the middle time between noon of the given day and the given time on that day. Thus, for the example above given : The given time is Dec. 19-9d: the middle time, therefore, between Dec. 19d. at noon and Dec. 19·9d. is Dec. 19-45d. This agrees with the result as already obtained by second differences Conclusion It is surprising that no intimation has been given in the explanation N.A. as to the above. There is not one word said as to how the differences were obtained: on the contrary, the explanation given must certainly lead any reader to infer that they are calculated in the usual way. It is true that a hint is given in the rule for the equation of time; but in a matter of such importance, the rules ought to be given explicitly, and not left to the reader to be guessed at. I would certainly say that nautical men will never trouble themselves by proportioning for hourly differences. Astronomers, I should think, would have preferred the old method by the first differences; and when great accuracy is required, to correct by second differences. If such ambiguity of explanation is continued in the Nautical Almanac, it may share the same fate as a treatise on music, which was declared too mathematical for musicians and too musical for mathematicians. In conclusion we would recommend nautical men to find the correction of the declination by means of the daily difference and proportional logarithms for 24 hours, as in Norie's table xxxiii.; and we trust that this method will be adopted at the examinations by the Marine Boards. Mathematical Investigation. Notwithstanding the remarks made above, it must be admitted that the new plan for hourly difference is a very ingenious method for finding the declination as correct as by using second differences. This may be proved as follows: Taking the same example as before, |