Page:Popular Science Monthly Volume 61.djvu/214

208 which would be the most favorable time. His position on the wave will be at S. If he is able to travel up the bay as fast as the wave he will keep his position near the crest, that is at S. But he can hardly do that, especially as the current would be very slight, and in the broad bay hardly strong enough for his guidance. Let us suppose that by the time he reaches Benicia, B, he has fallen behind the wave until he has the position at S'. It is then slack low water, and he can make no headway. Soon the next wave reaches him and he is in flood-tide. He will therefore swim back against the current. As the wave is going up the bay and he is going down, he soon gets past the crest and finds himself in the ebb-tide at S". He then turns and stems the ebb-tide, and as the wave is going in the same direction he is, he goes much beyond Benicia, B, before he again falls back to slack low water at S'", and gets into the flood of the next tide-wave.

By taking the statistics of the daily catch of salmon at various points, we have been able to trace the progress of a school up stream, and find that it requires four days to pass from Vallejo to Sacramento. We have been unable to determine the length of time required to reach Vallejo after leaving the ocean.

The spring run passes up the river quite rapidly, reaching their spawning grounds in the McCloud River in about six weeks after entering the river at Collinsville. The fall run moves more slowly. The flood and ebb tides are more nearly equal, owing to the small amount of water coming from the rivers, which makes a longer passage through