AND OTHER WATER WAVES 25 



plained his method of measurement, and detailed 

 the attendant circumstances of wind, weather, and 

 environment. This may have led to the rejection 

 for the purpose of this book of good measurements, 

 but the importance of all measurements or estimates 

 of the size of sea waves being accompanied by a 

 statement of the method of observation and the 

 attendant circumstances cannot be too strongly 

 emphasised. 



The relation between the wave-length in deep 

 water and the period (or time which elapses 

 between the passage of a fixed point by two 

 succeeding wave -crests) has been calculated 

 mathematically, and verified by observation. I 

 have, therefore, in what follows applied the formula 

 thus obtained, viz. : 



Wave length = 5^ x square of period, 



to obtain the wave-length when only the period 

 has been measured. In all cases, however, the 

 reader is informed which observation was made, 

 that of length or period. 



WAVES ON PONDS 



As the sea is always heaving with the disturb- 

 ance due to former winds, the commencement of 

 the wave -making action of wind is best observed 



