TIDAL OBSERVATIONS. 125 



for Fort Point out of " even two complete years " observations, and the un- 

 doubtedly approximate attainment of that result by Mr. Roberts, from one 

 year only, which his letter indicates. 



53. The funds at the disposal of the Committee have not sufficed to 

 emploj' calculators to push forward the work as energetically as the Report 

 to the Exeter Meeting recommended. What has been actually done has been 

 done entirely by Mr. Roberts, with only some slight assistance of a compa- 

 ratively mechanical kind in the way of preparing tables and forms for 

 calculation. 



The following is his own statement of the work done for the Committee ; — • 



§§ 54-70. Statement hj Mr. E. Roberts of work performed by him for the 

 Tides Committee, from the Exeter Meeting till August 6, 1870 (including 

 also the results of the analysis of the second yearns obsei'vatioTis at Kur- 

 rachee, obtained since tJie Liverpool Meeting). 



54. The diagram sheets of the Liverpool tide-gauge promising to give as 

 good results as can most probably be obtained from any system of self- 

 registration at present in use, were selected for further reduction and ana- 

 lysis. Two years' observations following the year whose results arc con- 

 tained in the Report for 1868, §§ 31-34, have been reduced and analyzed in 

 a similar manner. The results agree very satisfactorily with those of the 

 preceding year. The mean height of the water for the last two years is 

 slightly in excess of that found for the first year. In addition to the six 

 scries, S, M, L, N, K & 0, already defined, three others, representing the 

 solar diurual (declinational) tide, whose argument is (y— 2»/), called hereafter 

 for brevity P, and the two components of the solar elliptic semidiurnal 

 tides (R and T), whose arguments are 2 (y—^ii) and 2 (y — |jj)» were also 

 included. The solar elliptic semidiurnal tides require a period of two years 

 for their evaluation, by the method we have hitherto followed. The hour- 

 angle for the commencement of the second year was taken as twelve hours 

 in advance of the hour-angle assumed for the first year. As the two years 

 commenced on the same day of the year, the error involved in this assump- 

 tion is only 0°'25, a quantity which may be reasonably neglected in the 

 analysis of these tides. A Table extending through one year has therefore 

 been used in the composition of the series, and the years 1857-58 and 

 1858-59 combined for the determination of one value, and 1858-59 and 

 1859-60 for another determination. 



55. Referring the fictitious stars to their true positions at the commence- 

 ment of each year, by correcting the assumed hour-angles (the same table of 

 hour-angles having been used for the three years) by the difference between 

 the true and assumed places, and neglecting all terms which are very small 

 and not theoretical tides, we have the following sets of values : — 



1857-58. 1858-59. 1859-60. 



Ag 167192 i6*8ao8 168289 



Average inclination of 

 Moon's orbit to 

 Earth's equator. 



28° 28' 27° 56' 26° 58' 



