SURGES. 195 



From this table we see that the mean amplitudes of the waves at the three stations 



are 



Hut Point 

 Snow Hill 

 Gauss 



Mean amplituJf 

 max.-min. 



. -701" 

 . -581" 

 . -454" 



We have now shown that it is possible to recognise the same surges not only in the 

 Ross Sea area but also at places in the Antarctic so far apart as Hut Point, Snow Hill 

 and the Gauss Station. Unfortunately we have had to use different periods of observation 

 for the two groups of stations, and therefore the values of the amplitudes in the two groups 

 are not directly comparable. This is clearly seen when we compare the mean value for Cape 

 Evans in 1912, -400", with the mean value for Hut Point in 1902, -701", although the two 

 stations are so near together that they may be considered as one for our present purpose. 

 There can be little doubt that the surges were abnormally developed in 1902, and it is largely 

 due to this circumstance that we have been able to recognise the individual surges with 

 such confidence at such widely separated stations. 



For McMurdo Sound (Cape Evans and Hut Point) we have four years' observations, and 

 we have used all these to find the mean amplitude of the surges given in table 111, which 

 was -536". It is very likely that the relative amplitude at the stations remains fairly constant 

 from year to year, hence by multiplying each of our two sets of observations by the factor 

 necessary to bring the respective values for the McMurdo Sound stations to their average 

 value, we obtain reduced amplitudes for all the stations which are comparable. Thus the 

 amplitudes in 1912 require to be multiplied by |^ and those in 1902 by i^' 

 this has been done, we have the following relative amplitudes. 



^Vhen 



Table 114. 

 Pressure surges, amplitudes reduced to common period. 



It will be noticed that with the exception of Snow Hill and the Gauss Station, the 

 amplitude decreases with the distance from the Pole. It will be found, however, that they are 

 only roughly proportional to the latitude. When the mimbers are plotted on a globe, it is 

 found that they are more nearly symmetrical around a position about 10° away from the Pole. 

 By a series of trials and errors it was found that the amplitudes were nearly inversely 

 proportional to the distances of the stations from the position 80° S. 120° W. If one takes 

 as the ampitude of the surges at this position '677" and calculates the amplitude of the other 

 stations on the assumption that the amplitude decreases from this position lineally at the rate 

 of •162" per thousand miles, the amplitude at the stations are shown in the following table : — 



