82 THE FRESH-WATER LOCHS OF SCOTLAND 
observable under ordinary circumstances in a lake ; ^ but the experi- 
ment is interesting in view of the important discovery recently made 
by the Japanese observers,^ that the secondary oscillations in many of 
the bays on the coast of Japan are seiches, having a node at the mouth 
and a loop at the bottom of the bay. These oscillations, which are 
sometimes of considerable range, are apparently due to resonance with 
comparatively inconspicuous undulations in the external oceanic swell, 
the periods of which are equal to some of the natural periods of 
the bay. 
It was also possible, by means of a trough like that described 
above, but of different dimensions (length, 5 feet ; breadth, 4 inches ; 
depth, 5 inches ; depth of water, 3 inches), to illustrate during a 
lecture at the Royal Institution the generation of seiches in an ordinary 
lake by periodic variations of the surface pressure. By laying a sheet 
of tin on the top of the trough, an air-channel was formed over the 
surface of the water. Through this channel air could be blown by 
means of a Blackman's fan, and, by working a slider timed by the 
metronome, the air-current could be made intermittent. When the 
whole of the surface was covered over by the sheet of tin, the effect of 
the current, whether steady or intermittent, was merely to generate a 
train of progressive surface waves. But, when only half the length of 
the miniature lake was covered in, an intermittent current having the 
proper period generated a uninodal seiche. When a strip of tin 
dipping into the water at the end of the covering sheet just over the 
middle of the water was used to block the air-current, after a few 
alternations of the blast the amplitude of the generated seiche was such 
as to cause the water to splash over the ends of the trough. 
In like manner, by covering in the tank up to the theoretical 
position of the binode, a binodal seiche was generated, the parabolic 
surface of which at its culmination had about the same curvature as 
the parabolic bottom of the trough. 
Om the Vibrations which cause the Embroidery on 
THE LiMNOGRAM 
To the oscillations of a lake-surface having a period of less than 
2™, which under certain circumstances cause a regular or irregular 
embroidery on the limnogram, Forel gave the name of vibrations. 
The complete explanation of these vibrations can hardly be said to 
have been given as yet. They are, however, of great interest, because 
^ Endros, however, has given examples in j^oint, in some cases of constricted 
lakes, where a seiche in one part forces a seiche of the same period in another part. 
^ "Secondary Undulations of Oceanic Tides," by Honda, Terada, Yoshida, and 
Isitani, Journal of the College of Science, Im'perial University, Tokio, vol. xxiv. 
p. 1 (1908). 
