NATURAL PHILOSOPHY. 129 



same space of time. Another nnexplainable peculiarity of this 

 tidal freak is, that the water from the sea wouhl run up to one side 

 of the channel and down the other side at the same time." 



The same day irregularities in the tides in the Oakland Creek 

 were noticed by several persons. The tide alternately rose and 

 fell, and it was observed, at the foot of Washington Street, in 

 Oaliland, that, while drift-wood floated towards the mouth of 

 the creek, the water was gradually rising. On the morning of the 

 13th, according to a telegram from San Francisco, which appeared 

 at the time in tlie *' Tribune," a series of waves commenced flow- 

 ing upon the coast off San Pedro, causing the tide to rise 63 or 64 

 feet above the ordinary high-water mark, which was followed by 

 the falling of the tide an equal distance below the usual low-water 

 mark. The rise and fall occurred regularly every half hour for 

 several hours. Thus it appears that the tidal upheaving produced 

 by the earthquake travelled nearly 4,000 miles in about 36 hours. 



An earthquake wave which followed the recent eruption in the 

 Sandwich Islands was transmitted to the Pacific coast, and re- 

 corded on the government self-registering tide-gauges at San 

 Francisco and Astoria, in about 6 hours. 



The great tidal wave from Hawaii reached this coast, distant 

 over 2,000 miles, in 5 hours, and was observed along a stretch of 

 shore over 13 geographical degrees in length. These earthquake 

 waves appear to have moved with a velocity of about 400 miles 

 an hour. 



The papers have lately announced the terribly destructive force 

 of waves of the sea, produced by earthquakes in the West India 

 Islands. Prof. Brocklesby, in his "Elements of Physical Geog- 

 raphy," states some facts of an interesting character in reference 

 to the velocity of these waves. On the 22d of December, 1854, 

 immediately after an earthquake, the sea rolled in upon the town 

 of Simoda, in Japan, in a wave 80 feet high, overwhelming it in 

 an instant. After the wave fell, there were only 4 feet of water 

 in the harbor. Four or five similar waves followed at intervals, 

 completing the destruction of the town. 



Prof. Bache, by observations made on the tide gauges at San 

 Francisco and San Diego, which registered all changes in the sea- 

 level, discovered that these earthquake waves at Simoda travelled 

 across the Pacific. Tlie distance from Simoda to San Francisco is 

 4,527 geographical miles, which was traversed by the waves in 12 

 hours and 28 minutes, or with a velocity of 6 miles a minute. At 

 San Diego, which is 4,917 miles distant from Simoda, the waves 

 arrived an hour later, the velocity being sensibly the same. The 

 curious fact is stated, that the breadth of a wave, its velocity, and 

 the depth of water in which it travels, have been found by Prof. 

 Airy to have a relation to one another. For example, a wave 

 100 feet broad, travelling in water 100 feet deep, has a velocity of 

 15 miles an hour ; while a wave 10,000 feet broad, travelling the 

 ocean with a depth of 10,000 feet, advances with a velocity of 154 

 miles per hour. So that, given the velocity of a wave and its 

 breadth, the depth of the water may be calculated. Prof. Bache, 

 from these data, calculated a depth of the Atlantic, and found it 



