20 
of lantern diagrams the theory of colour vision was explained by 
the lecturer. The methods used for testing for colour blindness 
are (I) the lantern test; (2) the classification test by means of 
coloured wools ; and (3) the spectrum test. The wool method 
was declared by the lecturer to be unsatisfatcory, many normal 
sighted being thereby rejected, while intelligent colour-blind persons 
frequently fail to be detected. 
Friday, December 4th. Dr. G. D. Pidcock in the chair. 
Mr. J. C. Maxwell Garnett, M.A., gave a lecture on ‘‘ The 
Birth of the Moon,” in which the history of the moon was 
traced back to the time when it was thrown off the still fluid earth 
and forward to the time when it will again closely approach its 
parent planet. 
After insisting upon the importance of the search for knowledge 
for its own sake, without hope of reward, and with no regard to 
its practical application, the lecturer gave some account of the 
true scientific method of investigation—the collecting of facts, 
the propounding of an hypothesis to explain these facts, the de- 
ducing of consequences, and the testing of the hypothesis. Striking 
instances of this method were supplied by Charles Darwin’s theory 
of the evolution of species by natural selection, and by his son Sir 
George Darwin’s theory of the evolution of the earth-moon system 
by the action of tides. The lecturer explained the formation of 
the two daily ocean tides by the action of the gravititional attrac- 
tion of the moon upon the waters, and described how the main 
tidal waves, generated principally in the Pacific Ocean, become 
highly complex as they travel through seas and straits. A wave 
will travel more slowly in shallow than in deep water; indeed, 
nowhere is the ocean deep enough to allow the tidal wave to travel 
as fast as the earth rotates. Hence the tides are greatly delayed, 
the tide at London, for instance, having been generated in the 
Pacific two days before its arrival. The earth, rotating under 
the tidal waves, is subjected to friction, in consequence of which it 
is being slowly retarded and the day is being lengthened. An 
important deduction from Newton’s laws of motion is that the 
total amount of spin or angular momentum of a system of bodies 
remains constant whatever be the interactions among these bodies. 
It follows then that, if the moon be checking the earth’s spin, it 
must be increasing its own. This it is doing by increasing its 
distance from the earth. Sir George Darwin traced this process 
backward in time, and arrived by mathematical calculation at 
