206 POPULAR LECTURES AND ADDRESSES. 



" regular " according to the simple European rule, 

 but to be complicated by large differences between 

 the heights of consecutive high-waters and of con- 

 secutive low-waters, and by marked inequalities of 

 the successive intervals of time between high-water 

 and low-water. 



On the coasts of the Mediterranean generally the 

 tides are so small as to be not perceptible to 

 ordinary observation, and nothing therefore has 

 been hitherto generally known regarding their 

 character. But a first case of application of the 

 harmonic analysis to the accurate continuous 

 register of a self-recording tide-gauge (published 

 in the 1876 Report of the B.A. Tidal Committee) 

 has shown for Toulon a diurnal tide amounting on 

 an average of ordinary midsummer and mid-winter 

 full and new moons to nearly 4/5 of the semi- 

 diurnal tides ; and the present communication con- 

 tains the results of analysis showing a similar result 

 for Marseilles ; but on the other hand for Malta, a 

 diurnal tide (similarly reckoned), amounting to 

 only 2/9 of the semi-diurnal tide. The semi- 

 diurnal tide is nearly the same amount in the three 

 places, being at full and new moon, about seven 

 inches rise and fall. 



The present investigation commenced in the 

 Tidal Department of the Hydrographic Office, 

 under the charge of Staff-Commander Harris, R.N., 

 with an examination and careful practical analysis 

 of a case greatly complicated by the diurnal in- 



