2 RECORD AND REDUCTION OF THE TIDES. 



arranged with a wheel and index, and dependent on her rise and fall for its 

 rotation."^ 



In order to ascertain the nature of the tides, as well as the degree of accuracy of 

 the different observations, the readings were roughly plotted for a first examina- 

 tion ; the following series were found suitable for discussion : — 



Series I. From October 10th, 1853, to December 2Sth, 1853. — This series, with 

 the exception of three days, is complete ; the observations in the latter part of 

 December appear to be of less reliable character. The observations between Sep- 

 tember 11 and October 4, 1853, are too fragmentary to be used. The pulley-gauge 

 observations between October 4 and October 9 seem to have been only experi- 

 mental. The hourly readings are superseded by half-hourly readings on November 

 8, and continue half hourly, day and night, to the end of the series. After 

 November 28, corrective soundings were taken at noon each day. In order to 

 make use of these soundings, the mean depth of the water at the anchorage was 

 deduced from them as follows : — 



Mean reading. 



December, 1S53. 43.8 feet, from 31 souiidiiigs (:il noon). 

 January, 1854. 44.9 21 



Fel)rnary, " 44 3 17 



March, " 43.3 19 



April, " 41.8 20 



May, "43.5 9 



The individual soundings will appear in the record following. 



Mean depth of water at anchorage, in winter, 1853-54, 43.6 feet, as obtained 

 from 117 soundings. The monthly mean values for the tidal level accord well, 

 and show that no lateral change took place in the position of the brig (or else that 

 the bottom was level). It will be seen that for Series I the reading 7.0 was 

 adopted to express the mean level, the zero of the scale was, therefore, at an eleva- 

 tion of 36.6 feet from the bottom. The readings of the pulley guage are expressed 

 in feet," as 1 have been informed by Mr. Sonntag. 



Series II. From January 28th, 1854, to April 1th, 1854. — The double half-hourly 

 readings of the pulley-gauge are continued. The series is complete with the 

 exception often days, which had to be omitted. The register broke January 22d; 

 observations commenced January 24th, but were not sufficiently regular for use 



' The following note is appended : One end of the cord represented a fixed point, by being anchored 

 to the bottom; the free end, with an attached weight, rose and fell with the brig, and recorded its 

 motion on the grooved circumference of a wheel. This method was liable to objections, but it was 

 corrected by daily soundings. The movements of our vessel partook of those of the floe in which she 

 was imbedded, and were unaccompanied by any lateral deviation. 



" Tiic following is an e.xtract from Mr. Sonntag's letter to me, dated New York, March 23, 1860: 

 "The circumference of the wheel (of the pulley-gauge) was divided into feet and tenths of a foot, and 

 the records by the sounding line are also expressed in feet and decimals. The records of the wheel 

 arc very uncertain, as often the rope slid over the wheel without turning it, owing to the ice which 

 surrounded the axis." 



