TIDAL OBSERVATIONS 593 



The values obtained from (55), (56), and (57) are as follows : 



Cape Flora Teplitz Bay 



Ft. Ft. 



From (55) MSL .......... 6.076 4.133 (58) 



From(s6)HTL .......... 6.085 4-155 (59) 



From (57) HTL .......... 6.088 4.138 (60) 



By adding the values of (51), (52), (53), and (54) to those of (58) we obtain the corre- 

 sponding readings upon the tide staves, thus : 



Cape Flora Teplitz Bay 



Ft. Ft. 



Tropic HHW ........... 6.613 4-754 ( 6 



Tropic LHW ........... 6.486 4.579 (62) 



Tropic HLW ........... 5.923 3.714 (63) 



Tropic LLW ........... 5.331 3.485 (64) 



The difference between the two tropic high waters (HHW LHW) is called the tropic 

 high-water diurnal inequality in height, abbreviated to tropic HWQ or often to HWQ alone, 

 the word tropic being understood. In a similar way the tropic low-water diurnal inequality 

 in height (HL,W LLW) is contracted to LWQ. The great tropic range (HHW LLW) is 

 contracted to Gc, while the small tropic range (LHW HI, W) is represented by Sc. These 

 values from (61) to (64) are as follows : 



Cape Flora Teplitz Bay 



Ft. Ft. Ft. Ft. Ft. Ft. 



Tropic HWQ . .6.613 6.486 = 0.127 4.754 4.579 = 0.175 (65) 



Tropic LWQ . . 5-923 5-331 =0.592 3.714 3.485 = 0.229 (66) 



Tropic Gc . .6.613 5.331 = 1.282 4.754-3.485=1.269 (67) 



Tropic Sc . .6.486 5.923 = 0.563 4.579 3.714=0.865 (68) 



The difference between the mean of the higher high waters and the mean of the lower low 

 waters for one or more months is called the great diurnal range, and is abbreviated to Gt. It 

 may be computed as follows, when either tropic HWQ or LWQ is approximately as great as 

 one-fourth of the mean range : 



Gt = 0.75 Gc + 0.25 Mn (69) 



The range of the diurnal wave may be found from the harmonic constants, putting 2D 

 to represent the wave, by the formula 



2D,= 2.042 (K. + 0.) (70) 



From (69) and (70) we obtain : 



Cape Flora Teplitz Bay 



Ft. Ft. 



Gt ............... 1-203 1-236 (70 



2D, ............... 0.606 0.292 (72) 



The perigtan and apogcan ranges are due to the moon's varying distance, and may be 

 obtained from the harmonic constants by the following formulas : 



(73 , 



(74) 



in which the words perigean and apogeau are abbreviated to their first and last letters. 



