The Tides. 211 



The two equal tides take place when the moon has no decana- 

 tion, i. e., when in the plane of the earth's equator no matter what 

 its position otherwise may chance to be. When the moon moves 

 north or south of the equator the tides become unequal. In 

 most localities the highest of the two will be the one follow- 

 ing the upper transit during north declinations and lower tran- 

 sits during south declinations; when the tides observed do* 

 not succeed the transit which attends their formation, the exact 

 reverse of this is true. Leaving aside the semi-diurnal inequal- 

 ities, the highest tides occur at new and full moon and are knowQ 

 as s-pring tides^ the least tides occur when the moon is in her quad- 

 ratures and are known as neap tides. The highest of the high 

 tides occur when the full or change takes place during maximum 

 declinations, then one of the waves is much larger than the other, 

 in some localities the inequality is so great as to compound the 

 two waves to such a degree that only one distorted wave is ap- 

 parent in 21 hours. 



The mean time from the moon's upper transit to the succeeding 

 high water, during a lunation, is called the " Corrected Establish- 

 ment " or the " Establishment of the Port." The establishment 

 is used by mariners and others for calculating the time of the tide 

 from the position of the moon. 



In the Gulf of Mexico the tides are more complicated ; in Gal- 

 veston Bay two very small irregular tides are observable in 24 

 jjours when the declination of the moon is small, when this in- 

 creases either way, the two become unequal until only one high 

 water is recognizable in 24 hours ; this continues several days be- 

 fore and after maximum declination. 



By careful obseavations the two compounded waves are observ- 

 able unless affected by local disturbances which latter often 

 exceed the range of the tide which is from one-half to two feet. 

 The foregoing facts illustrate the general features of the tides 

 and warrant the assumption that the moon is in some manner 

 connected with the same. 



If we examine the coast lines of continents we will observe a 

 general similarity in some while in others we may even compare 

 their details and in either case find remarkable resemblance which 



