RECORD AND REDUCTION OF THE TIDES. 3 



until January 28th. The corrective soundings at noon are continued, with occa- 

 sional omissions, throughout this series. After April 7th there is a break in the 

 observations, those between the 14th and 20th appear to be irregular. 



Series III. From April 20th, 1854, to August 3d, 185 L— The double half-hourly 



readings of the pulley-gauge continue to May 5th, after which date single half- 

 hourly readings are recorded. The corrective soundings cease on the 12th of May. 

 Interruptions occur between May 4th and May 7th, also on July 8th, also between 

 July 15th and 18th, and between July 20th and the 28th. On the 8th of August, 

 the brig was released from her ice cradle, and rose two and a half feet ; occasional 

 warpings of the brig after this date render the observations worthless. On the 

 23d of August the brig was in but seven feet of water, and grounded. 



Series IV. From September 1th, 1854, to October 22d. 1854. — The hourly obser- 

 vations assume again a more regular appearance on the 7th of September; they 

 were taken with the sounding line, and are expressed in fathoms and feet (as stated 

 in a note, August 12th). The following note is of October 21st, 1854: "The tide 

 register as yet not rigged, observations very faulty by sounding line." The irregu- 

 larities increase after this date; on the 15th of November following, the tide 

 register was arranged, and observations (hourly) commenced on the 17th; the slip- 

 ping of the rope, however, was of so frequent occurrence and of so great an extent, 

 that it was considered better to take no further notice of these observations ; the 

 record continues to January 24th, 1855, when the strength of the party no longer 

 permitted due attention to the tidal phenomena. 



It was apparent that before any closer insight into the nature of these tides 

 could be obtained, they must first be reduced to the same zero or mean level of 

 the sea. To effect this in a manner apparently best suiting the case, and otherwise 

 unobjectionable, two curved lines were traced on the diagrams, the upper one 

 enveloping the highest high water of each day, the other enveloping the lowest 

 low water of each day ; in tracing these lines some allowance was made, when 

 necessary, for disturbing causes, so as to obtain tolerably smooth curves ; cases of 

 abrupt changes were, of course, treated accordingly. A line, equidistant from 

 these curves, was assumed as representing the mean level, and when straightened 

 out was adopted as axis of the mean level of the sea. The corrections to refer 

 each observation to this adopted mean level; or, in other words, the corrections 

 required to refer each observation to the same zero of the scale, so as to make them 

 comparable with each other, were taken from the projection, and are given in the 

 column headed " reduction," in the following record. 



This method of treatment excludes necessarily in Series I, II, and III, any dis- 

 cussion of the variation in the mean level of the sea, the oscillations of which have 

 been found small at other places. As an illustration of this, the tides at Singapore 

 might be referred to ; the Rev. W. Whewell (7th series of researches on the tides, 

 Phil Trans, of the Roy. Soc., Part I, 1837), finds for these tides that, if a line is 

 drawn representing the mean height (midway between high and low water each 

 day) it is very nearly constant, though the successive low waters often differ by six 



