ISO Prof. G. H. Darwin. [Jan. L' ( ., 



January 29, 1891. 

 Sir WILLIAM THOMSON, D.C.L, LL.D., President, in the Chair. 



The Presents received were bud on the table, and thanks ordered 

 for them. 



The Bakerian Lecture was delivered as follows: 



BAKERIAX LECTURE. * On Tidal Prediction." By G. H. DARWIN, 

 F.R.S., Plumian Professor and Fellow of Trinity College, 

 Cambridge. Received December lli, iKiH). 



(Abstract.) 



At most places in the North Atlantic the prediction of high and 

 low water is fairly easy, because there is hardly any diurnal tide. 

 This abnormality makes it sufficient to have a table of the mean 

 fortnightly inequality in the height and interval after lunar transit, 

 supplemented by tables of corrections for the declinations and 

 parallaxes of the disturbing bodies. But when there is a large 

 diurnal inequality, as is commonly the case in other seas, the heights 

 and intervals, after the upper and lower lunar transits, are widely 

 different ; the two halves of each lunation differ much in their cha- 

 racters, and the season of the year has great influence. Thus simple 

 tables, such as are applicable in the absence of diurnal tide, are of no 

 avail. 



The tidal information supplied by the Admiralty for such places 

 consists of rough means of the rise and interval at spring and neap, 

 modified by the important warning that the tide is affected by diurnal 

 inequality. Information of this kind affords scarcely any indication 

 of the time and height of high and low water on any given day, and 

 must, I should think, be almost useless. 



This is the present state of affairs at many ports of some importance, 

 but at others a specially constructed tide-table for each day of each 

 year is published in advance. A special tide-table is clearly the best 

 sort of information for the sailor, but the heavy expense of prediction 

 and publication is rarely incurred except at ports of first- rate comme 

 cial importance. 



There is not, to my knowledge, any arithmetical method in use 

 of computing a special tide table which does not involve much work 

 and expense. The admirable tide-predicting instrument of the Indian 



