1891.] Presents. 133 



errors of time fall on those very small rises of water which are of 

 frequent occurrence at Aden. 



I have made two other comparisons, one with the Indian predictions 

 of 1887, and the other with actuality of 1884. In the latter case, when 

 a few very small tides were omitted, the probable error was 7 m in the 

 time, and 1'4 inches in height. It is concluded from these compari- 

 sons that, with good values for the tidal constants, the tables lead to 

 excellent predictions, even better than are required for nautical pur- 

 poses. 



It is probable that this method may be applied to ports of second- 

 rate importance, where there are not sufficient data for very accurate 

 determination of the tidal constants. Suggestions are made for very 

 large abridgment of the tables in such cases, accompanied, of course, 

 by loss of accuracy. 



The question of how far to go in each case must depend on a 

 variety of circumstances. The most important consideration is, I 

 fear, likely to be the amount of money which can be expended on 

 computation and printing ; and after this will come the trustworthi- 

 ness of the tidal constants, and the degree of desirability of an accu- 

 rate tide-table. The aim of the paper has been to give the tables in 

 a simple form, and if, as seems certain, the mathematical capacity of 

 an ordinary ship's captain will suffice for the use of the tables, whether 

 in full or abridged, I have attained the principal object in view. 



Presents, January 29, 1891. 

 Transactions. 



Albany : New York State Museum of Natural History. Bulletin. 



Nos. 7-10. 8vo. Albany 1889-90. The Museum. 



Amsterdam : Koninklijke Akademie van Wetenschappen. Ver- 



slagen en Mededeelingen. Afd. Natuurkunde. Deel VI. 8vo. 



Amsterdam 1889. The Academy. 



Baltimore : Johns Hopkins University. Circulars. Vol. X. Nos. 



83-84. 4to. Baltimore 1890; Studies from the Biological 



Laboratory. Vol. IV. No. 7. 8vo. Baltimore 1890 ; Studies in 



Historical and Political Science. Series 8. Nos. 5-12. 8vo. 



Baltimore 1890 ; Annual Report of the University. 1890. 



8vo. Baltimore. The University. 



Peabody Institute. Annual Report. 1890. 8vo. Baltimore. 



The Institute. 



Basel: Naturforschende Gresellschaft. Verhandlungen. Bd. IX. 

 Heft 1. 8vo. Basel 1890. The Society. 



