228 Proceedings of Royal Society of Edinburgh. [sess. 
hitherto, or to times 1, 2, 3 . . . after mid- orbit passages. Lines 
drawn across the orbits through 1, 2, 3 ... on the left, show 
simultaneous positions of the ten particles at times 1, 2, 3 after mid- 
orbit. The line drawn from 4 across seven of the curved orbits, 
shows for time 4 after mid- orbit, simultaneous positions of eight 
particles, whose undisturbed distances are 0, T, . . . *7. Remark 
that the orbit for the first of these ten particles is a straight line. 
