On the Solar and Lunar Diurnal Tides of the Coasts of Ireland. Ill 



the direction of the ray upon the mirror. At first a diaphragm 

 was placed before the converging lens of the lamp, so that the 

 light struck the mirror alone, for I feared that the warming of 

 the air about the galvanometer might produce currents, and thus 

 distm'b the needle. It was found, however, that this precaution 

 was unnecessary, and that the full luminous sheaf might be per- 

 mitted, without prejudice, to fall upon the multiplier. In this 

 way it was much easier to cast a sufficient quantity of light 

 always upon the mirror, which, when the diaphragm was applied, 

 was a work of some difficulty ; for although the lamp was placed 

 nearly in the plane of the system, it was necessary to keep it at 

 a certain distance from the multiplier, so that its own magnetic 

 power exercised no influence on the needle. With the distance, 

 however, it is plain that the difficulty of keeping the ray exactly 

 on the mirror increased in like proportion. 



On a screen about 2'0 metres in length, a vertical black line 

 marked the position of the luminous image when the needle was 

 undeflected. The distance of the mirror from the screen was 

 about 3 metres. The sensitiveness of the arrangement was 

 rather too great than too small ; as the muscular current drove 

 the needle and mirror against the stops, while a deflection of 

 even 11° was sufficient to cause the image to leave the screen. 

 It was beautiful to observe, under the influence of the electro- 

 motive force of a minute nerve, or a few muscular fibres of a frog, 

 the luminous image flying through the lecture room 



XIV. On the Solar and Lunar Diurnal Tides of the Coasts of 

 Ireland. By the Rev. Samuel Haughton, Fellow of Trinity 

 College, Dublin. 



[Continued from p. 64.] 



Section VI. Diurnal Tide at Rathniullan. 



HAVING separated the solar and lunar tides in the diurnal 

 tide at RathmuUau, I obtained the following results : — 



I. Diurnal tide at high water. 



1. Maximumvalue of lunar tide for positive heights =0-29ft. 



2. Maximum value of lunar tide for negative heights = 0'47 ft. 



3. Maximum value of solar tide =0"23 ft. 



4. Diurnal solitidal interval =9*» 40"». 



5. Age of lunar tide =5*^ 10**. 



II. Diurnal tide at low water, 



1. Maximum value of lunar tide for positive heights = 0*1 3ft. 



2. Maximum valueof lunartidefornegativcheights = 0"20ft. 



3. Maximum value of solar tide =0*23 ft. 



4. Diurnal solitidal interval =9'^ 40"*. 



5. Age of lunar tide =4'* 20''. 



