Wishing, primarily in connection with the obtaining of

necessary information for purposes connected with the

drainage of Hobart, and secondarily, to fix the mean sea level

for geodetic and engineering matters, to get a series of tidal

observations, I spoke to Captain Oldham, of H.M.S. "Egeria,"

on the subject and he at once arranged to fix the automatic\ud
tide gauge of his ship on the New Wharf, and to have

observations taken for as long a period as the sojourn at

Hobart permitted. I am indebted to him for the accompanying

remarks and tables of observations

Mault, Alfred

Wishing, primarily in connection with the obtaining of

necessary information for purposes connected with the

drainage of Hobart, and secondarily, to fix the mean sea level

for geodetic and engineering matters, to get a series of tidal

observations, I spoke to Captain Oldham, of H.M.S. "Egeria,"

on the subject and he at once arranged to fix the automatic

tide gauge of his ship on the New Wharf, and to have

observations taken for as long a period as the sojourn at

Hobart permitted. I am indebted to him for the accompanying

remarks and tables of observations

University of Tasmania Open Access Repository

8ON SOME TIDE OBSERVATIONS AT HOBAETDURING FEBRUARY AND MARCH, 1889.Bt a. Mault.Wishing, jDrimarily in connection with the obtainiiDg ofnecessary information for purposes connected with thedrainage of Hobart, and secondarily, to fix the mean sea levelfor geodetic and engineering matters, to get a series of tidalobservations, I spoke to Captain Oldham, of H.M.S. "Egeria,"on the subject and he at once arranged to fix the automatictide gauge of his ship on the New Wharf, and to haveobservations taken for as long a period as the sojoura atHobart permitted. I am indebted to him for the accompany-ing remarks and tables of observations. To enable him toconnect his observations with the level of some permanentobject on shore, I took the levels from the town datum markfixed to one of the steps of the Town Hall to the graduatedstaff fixed at the New Wharf in connection with the gauge.In his letter to me enclosing the remarks and tables.Captain Oldham says :—" From these observations the ' mean"tide level' is 8ft. 2' 7 inches on the gauge, or 35'255 feet" below the datum mark on the Town Hall." Please note that these observations are only for one" month, and that, as probably the mean tide level varies at" different seasons, to get satisfactory results, a year's" observations should be obtained—this could easily be done" with an automatic gauge."I am glad to say that this will be done, as the HobartMarine Board is taking the necessary steps to procure andfix such a gauge. When it arrives I shall be happy to fixthe graduated staff so as to coincide with the datum ofCaptain Oldham's observations.The following are Captain Oldham's remarks and observa-tions :—"Remaeks on Tides Observed at Hobart.February and March, 1889.1. The tides are subject to a large diurnal inequality; thehighest high water is followed by the lowest lowwater, the tide then rises to a lesser high water, andfalls to a lesser low water.2. With the moon's declination north, the higher highwater follows the superior transit of the moon ; withthe moon's declination south the higher high watersucceeds the inferior transit.3. The greatest range of tide appears to occur about twodays after the moon has reached its greatest north orsouth declination, the least range when the declinationis zero.BY A. MAULT.4. H.W.F. & C. occurs at Hobart at 8h. 15min. Springsrise/S|to4ifeet/^^^® land 2 feet.REGISTER of TIDES observed at HOBART in tbe Month ofFEBRUARY, 1889.Neaps 2^ feet.10 SOME TIDE OBSERVATIONS AT HOBAET.For the purpose of more readily comprehending tlieinformation contained in these observations, I have prepareddiagrams—the greater j)art drawn to scale—and settingforth :—1st. The curve of tidal action for every day during wliichobservations were taken, from the 4th February tothe 6th March, showing the levels of high and lowwater in comparison with mean tide level, and thetimes at which they occurred.2nd. The moon's course so as to show the times of superiorand inferior transit of the moon's phases and apogeeand perigee.3rd. The moon's north and south, declination.4th. The intervals, called by Dr. Whewell " LunitidalIntervals," of time between the moon's transits andthe succeeding high water; the extreme intervalscaused by the diurnal inequality being faintlymarked, and the mean intervals more strongly.5th. Wind force and direction at every time of high water ;and6th. Barometric pressure at every time of high water.The graphic presentation of all these elements synchronicallyenables one to judge better of their influence upon the tide.The diurnal inequality of spring tides is not only shown,but is shown to follow the usual law, as pointed out byCaptain Oldham, in connection with the north and southdeclination of the moon. Equally clearly appears theoccurrence of springs at greatest declination, and not at newand full moon, so that at Hobarfc there is no " age of the tide ;'^and in connection with this the influence of perigee is shownin the higher tides at south declination. Captain Oldham'scaution is very useful while looking at these diagrams that wemust remember that we have here only one month's observa-tion. But it is not likely that a year's observations willinodify the above-mentioned facts. I believe they will bechiefly useful in showing that there is some regularity in thesequence and circumstances of the great apparent irregularitiesshown by these observations for one month. To show thenature and extent of these irregularities I have appended twodiagrams shovdng for comparison a fortnight's tide curves atHobart and a fortnight's at Bombay, and a diagram repre-senting a normal curve of lunitidal intervals in contrast withthe zig-zag mean line of such intervals at Hobart. Theseirregiilarities will, I think, show that no " estahlisJiment,"that is—time of high water on the day of new or full moon—can be fixed, although on the month's observations CaptainOldham mentions 8h. lom. At Hobart this is of no greatBY A. MAULT. 11conseqvieuce, as the depth of water in the harboui* is suchthat the comparatively small rise and fall of tide does notmuch affect sailing arrangements.It is, however, very desirable that the observations to betaken should be as complete as those given by CaptainOldham, and I would press on the Society the desirability ofco-operating with the Marine Board to secure this. Theimportance of the registration of the actual tidal actionspeaks for itself, and equally so does the necessity of comparing continually such action with the age and position ofthe moon. The force and direction of the wind have alsoan influence that must be noted. In connection with this Imay mention that during this month's observations, as shownon the large diagram, the highest tides occurred with thewind blowing from north, and north-easterly points—that ismore or less down the Channel. The barometer should alsobe carefully observed, if a mean sea level is to be fixed, as afall of one inch in the barometer means a rise of 20 inchesin the sea level.Another important matter can only be secured by the co-operation of the Marine Board;—the progress of the tidewave round the coast. I would suggest that they be askedto get their lighthouse men to keep a register of the actualtimes of high and low water as nearly as can be ascertainedby them during all the time that registers are being kepthere. This is a matter of general interest.I have to apologise to the Society for the presentation ofsuch a meagre paper, but must plead the engrossing natureof my other occupations, and the time that the preparationof the diagrams has taken. But I hope I have said enoughto show the desirability of pursuing investigation in thischannel.DiscTJSsioisr.Mr. A. Gr. Webster stated that the Marine Board wouldbe willing to render any assistance in its power.Sir Lambert Dobson said that a namesake of his, whowas head-master of the High School, had manufactui-ed anautomatic tide gauge himself, and kept a register of tides forsome time. He could not say when it was, but he thought itwould be about 1853.Mr. W. E. Shoobridge stated that at one time he used toregister the tide in the Derwent, and found it varied verymuch, the lowest tides occurring about February and March.His Excellency thought it would be very important tohave the observations in regard to the tidal wave around the12 DISCUSSION ON SOME TIDE OBSERVATIONS AT HOBART,country. With regard to tlie point raised by Sir LambertDobsoD, lie had been told by fishermen and others that lowtides were a sign of fine weather, and high tides of bad weather,and if they had a series of observations extending over sometime the value of them in this direction would be seen. He hadthought the highest tides would have been experienced whenhigh winds blew in through the Channel, keeping the waterup, instead of finding the highest tides when the winds camefrom the N". or JST.E., as Mr. Mault had stated.

On some tide observations at Hobart during February and March, 1889

http://eprints.utas.edu.au/15820/1/mault-tide-observations-1889.pdf

On some tide observations at Hobart during February and March, 1889

Abstract

Similar works

Full text

Available Versions

University of Tasmania Open Access Repository