ON THE HARMONIC ANALYSIS OF TIDAL OBSERVATIONS. 33 



Second Report of the Committee, consisting of Professors G. H. 

 Darwin and J. C. Adams, for the Harmonic Analysis of Tidal 

 Observations. Drawn up by Professor Gr. H. Darwin. 



Diking the past year Major Baird Las been engaged in the transformation 

 of the tidal constants for the several Indian ports, as deduced from the 

 observatiors of previous years, to the form recommended in our first 

 report (1833). He also intends to treat the European tidal results, pub- 

 lished in previous Reports of the Association, in the same manner. 

 Under his superintendence auxiliary tables have been prepared and 

 printed in India for the use of the computers ; a portion of these tables 

 was given at the end of the Report of 1883. The current work at 

 Poona is now being carried out in accordauce with our suggestions. 

 Forms have been prepared by Mr. Roberts for the rednction of the new 

 compound tides MK, 2MK, ALN (see Schedule H., Report of 1883) ; but 

 I have not heard whether the range of any of these tides has been found 

 to be sufficiently great to make it desirable that the reductions should be 

 continued. The recommendations with regard to the tides M[ and L have 

 not been yet sufficiently tested, but the procedure is certainly theoretically 

 correct. 



An unexpected delay has occurred in the preparation of the new 

 forms for the tides of long period, bat they are to be complete by the 

 beginning: of November. 



It has been found expedient to depart somewhat from the form 

 recommended in Schedule R for the entry of the diurnal means from 

 which these tides are reduced. The table is now divided into two parts ; 

 the rows marked 'change ' are put together, and form the second half of 

 the table. In the case of the tide MSf, to which Schedule R applies, 

 the mode of the entry in the new forms will be thus. The values for 

 days 0, 1, 2, 3, are entered from left to right in the first half ; then, in 

 the second half, entries 4, 5, 6, 7 are inserted from right to left, and 8, 9, 

 10, 11 from left to right; then we ascend to the first half again, and 

 enter two rows, namely, 12, 13, 14 from right to left, and 15, 16, 17, 18 

 from left to right, and so on alternately. In both halves of the table the 

 positive entries are put to the left and the negative to the right. The 

 summations are carried out independently in the two halves, and the signs 

 in the sums of the lower half are changed, before the final sums of both 

 halves are formed. 



In the preface to the Report of 1883 the intention was expressed of 

 sending copies of the computation forms to certain public libraries, and a 

 grant of money was made by the Association for the purchase of these 

 copies. Complete copies have not, however, been as yet obtainable, on 

 account of the delay in the preparation of the forms for the tides of long 

 period. 



Up to the present time the forms have been privately printed for the 

 Indian Government, and as they have not been on sale, this method of 

 harmonic analysis has been inaccessible to the public. To meet this want 

 I have been making arrangements for producing an edition for sale. In 

 the course of a month or two the copies will be on sale, 1 at a price not 

 yet determined on. I have received much assistance towards the ex- 



1 By the Cambridge Scientific Instrument Companv, St. Tibbs' Eow, Cambridge. l 

 1884. d 



