26 [Dee. 16, 
Haupt. ] 
forces which have produced the observed effects. It now re- 
mains to determine why this resultant should be sometimes 
from the north-east and at other times from the south-east. 
This leads at once to an examination of the phenomena at- 
tending the approach of the tidal wave and the position of 
the éotidal lines with reference to the coast line. For this 
purpose there are available the general cotidal maps of Prof. 
Guyot, and the more detailed maps of Prof. Bache, accom- 
panied by the tide tables of the Atlantic coast, as contained in 
the United States Coast Survey Reports. Meagre as these 
data are, they are yet sufficiently abundant to confirm the ex- 
istence of the alleged resultant movements, and to verify in 
the most satisfactory manner the reliability of this method of 
determining the forces by their effects. 
Although the phenomena of tidal movements in the open 
ocean are but little understood, it is well known that they are 
sensibly modified by the topography of the coast line. 
Professor Bache says that ‘‘ where a bay or indentation of 
the coast presents its opening favorably to the tidal wave and 
decreases in width from the entrance towards its head, it is well 
known that the tides rise higher and higher from the mouth 
upwards,” while Lentz, in his “Ebb and Flow of the Tides,” 
says: 
“The intricate, theoretical, tide-generating conditions are 
complicated by a number of circumstances, forming a be- 
wildering labyrinth of causes and results, through which the 
human mind cannot find its way.” 
“The numberless tidal waves rushing through the ocean in 
all directions may be compared to those formed by throwing 
ten (10) or twenty (20) stonesinto a small pond. By watching 
these we may learn as much as we know about the tidal waves 
moving on our ocean,” and he adds, “this certainly is discour- 
