1878.] Observations in the Gulf of Ciitch. 43 



*'■ Great credit is due to Capt. Baird for the manner in which he con- 

 *' ducted the task entrusted to him. The difficulties he had to contend with 

 *' in obtaining exact registrations continuously for such long periods were 

 " very serious and formidable ; all the stations were situated at points on the 

 " coast line which were very far from the nearest habited localities ; and the 

 " insj^ections during the season of monsoons, which work was done entirely 

 " by himself, necessitated constant travelling during the most inclement time 

 " of the year, and entailed an amount of risk and exposure which would tell 

 *' on a constitution of iron." 



Final Besulfs. — The analysis of the results of the observations has 

 necessarily been a work of time and has only lately been completed. Col. 

 Walker felt assured that it would be best performed with the assistance of 

 Mr. Eoberts of the Nautical Almanac Office in London, by whom all the tidal 

 observations taken for the British Association had been, and are still being 

 reduced and analyzed, under the superintendence of Sir W. Thomson, and 

 who had, previous to the commencement of the observations, aided Caj^t. 

 Baird in tlie preparation of an account of the practical application of the 

 harmonic analysis by which tidal observations are reduced for the British 

 Association. Sanction Avas therefore obtained for Capt. Baird to remain 

 in England and reduce his observations with Mr. Roberts' assistance. The 

 results will be presently stated. But first it is necessary to give a brief 

 epitome of the method of investigation which has been followed. 



The rise and fall of the level of the ocean, twice, or nearly so, in twenty- 

 four hours, is well known to be due to the attractions of the sun and the moon. 

 If the orbit of the earth and that of the moon were quite circular and lay 

 in the plane of the equator, and if the moon performed its revolution round 

 the earth in the same time that the sun appears to revolve around the earth, 

 then there would be two tides daily, differing from each other in form 

 — should the sun and moon not be in conjunction — but recurring alike from 

 day to day. The moon, however, makes her circuit of the earth in 48 

 minutes over the twenty-four hours, and thus the sun makes thirty apparent 

 circuits of the earth while the moon is only making twenty-nine ; more- 

 over, the orbits of the earth and of the moon are not circular, nor are they 

 situated in the plane of the equator. Thus the positions of the siin and 

 moon, relatively to the earth, are momentarily varying in distance, declin- 

 ation and right ascension. Consequently, the level of the ocean is subject 

 to momentary variations in the dynamical action of the disturbing bodies ; 

 and these cause a variety of tides which recur periodically, some in short, 

 others in long, periods. 



In the present investigations, the short and the long period tides have 

 been analyzed by different methods. The former — which here embrace all 

 tides recurring in pei'iods of or about a day in duration, and in any aliquot 

 part of the ^««6'«-diurnal period — have been treated in accordance with the 



