42 THE FRESH- WATER LOCHS OF SCOTLAND 
drawn to scale for a selection of different particles in the middle part 
of fig. 15 ; the upper part of the figure is a similar diagram for a 
tank of rectangular longitudinal section. The nature of the motion 
at various places may be demonstrated by dropping in red ink as 
before. In the present case the whole of the water is in motion, and 
the striking thing is that all the water particles keep exact time, like 
a company of well-drilled soldiers. Each particle is at the end of its 
orbit at the same time ; each at the arrow-marked end at the same 
time ; and so on. This collaboration is expressed mathematically 
by saying that the particles are always in the same phase, although 
Fig. 15. 
the directions and lengths ot the orbits vary from point to point. 
It is a matter of wonder that this should be the case for two particles 
12 feet apart in our experimental tank ; but it seems well-nigh in- 
credible, though unquestionably true, that the same holds good for 
two water particles at the two ends of the Lake of Geneva — that is to 
say, 45 miles apart. It was therefore not an obvious remark, but a 
brilliant generalisation, which Forel made long ago, when he asserted 
that the seiches of the Lake of Geneva were standing oscillations, 
similar in nature to the one which may be started in a 12-foot tank. 
By stirring with a period of about 2^ sec. at a distance from the 
end of our miniature lake = 0*21/, a standing oscillation of another 
description is raised, with two nodes each somewhat nearei' the ends 
