8 



ON SOME TIDE OBSERVATIONS AT HOBAET 



DURING FEBRUARY AND MARCH, 1889. 



Bt a. Mault. 



Wishing, jDrimarily in connection with the obtainiiDg 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 sojoura at 

 Hobart permitted. I am indebted to him for the accompany- 

 ing remarks and tables of observations. To enable him to 

 connect his observations with the level of some permanent 

 object on shore, I took the levels from the town datum mark 

 fixed to one of the steps of the Town Hall to the graduated 

 staff 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 Hobart 

 Marine Board is taking the necessary steps to procure and 

 fix such a gauge. When it arrives I shall be happy to fix 

 the graduated staff so as to coincide with the datum of 

 Captain 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; the 



highest high water is followed by the lowest low 

 water, the tide then rises to a lesser high water, and 

 falls to a lesser low water. 



2. With the moon's declination north, the higher high 



water follows the superior transit of the moon ; with 

 the moon's declination south the higher high water 

 succeeds the inferior transit. 



3. The greatest range of tide appears to occur about two 



days after the moon has reached its greatest north or 

 south declination, the least range when the declination 

 is zero. 



