126 
SHIDY. 
as given by Lagrange’s formula—that is, it corresponds to one- 
half of the trough just mentioned. The tidal motion of the 
rest of the Red sea imparts regular impulses to the waters of 
the Gulf of Suez, which behaves exactly as the water in the 
trough did—that is, it forms a nodal line at Tor with no tide, 
although having tidal currents. The phase of tide is reversed 
above and below the node, and it is high water at the same 
time all the way from Tor Bank to Suez. It is seldom that 
laboratory experiments fit so beautifully to the conditions 
of nature as in this case. 
In the Gulf of Maine, including the Bay of Fundy, the 
boundaries are not so regular and canal-like as in the Gulf of 
Suez, but there is considerable evidence of a stationary wave 
there. If we take Georges Bank as the southern or sea edge of 
the Gulf of Maine, its length to Eastport is about 200 sea miles, 
and to St. John, N. B., perhaps 40 miles more. The average 
depth is about 85 fathoms, which is just about the depth re¬ 
quired by Lagrange’s formula to produce one-quarter of the 
length of a free wave in the length of the gulf. If the con-, 
ditions were such that the basin had regular parallel side walls, 
the slope of the bottom near the shore reaching the average 
depth so quickly that the slanting portion was but a small 
fraction of the whole length, while the length of the basin 
was exactly that required for one-fourth of a free wave, 
gigantic tides would be formed. But, as only rough ap¬ 
proximations to these conditions exist, we have tides of 10 
feet in Boston harbor, far off to the extreme west of the Gulf, 
the range gradually increasing as the axis is approached 
until it becomes 20 feet at the entrance to the Bay of Fundy. 
This bay, being a shallowing and narrowing corner of the 
Gulf-of-Maine area, has an unusually large range of tide; 
but there is a further increase toward the head and in the 
arms of the bay, due to the fact that the energy of the pro¬ 
gressive portion of the wave is well conserved from point to 
point. The range becomes greater and greater as the cross- 
section diminishes, until at its head it attains the enormous 
range of 50 feet at spring tides, and sometimes, in rare in- 
