72 JOURNAL OF THE 
William Crookes, the learned President of the British 
‘Association for the Advancement of Science, by more 
than nineteen centuries in the prediction of the exhaust- 
ion of ‘tthe wern-out Earth.’’ True he did not fix upon 
1931 as the date of complete exhaustion still he evidently 
did not think it very far off. Like all sturdy conserva- 
tives he praised the good old times. 
B’en now the worn-out earth with age effete, 
* og that in her early prime € = ¥ 
To children of her care Spontaneous gave— 
In rich abundance gave the shining grain, 
Which now with labor huge she scant supplies 
In niggard pittance to more pressing wants, 
With weary steps we urge the weary ox, 
And turn exhausted fields, that scarce return 
Decreasing harvests to increasing toil. 
The aged ploughman shakes his.weary head 
So oft his labor unavailing proves: 
How oft doth he then repining chide his lot 
Comparing present times with past, exalt ' 
The fortune of his sires. 
Book. II p. 114. 
He gives a remarkable explanation of the nature of re- 
flected images. These are made up of 
Thin effigies and forms 
Which singly are unseen; but when outpoured 
In a continuous andimpulsive flow, 
Give by reflection, images of things. 
These effigies ‘‘wander not alone.’’ They ‘‘fill the 
embracing air with floating forms.’’ This is proved by 
the fact that in whatever direction the mirror is turned, 
‘straight in its silent depths the scene responds.’”’ The 
reversal of the image in the mirror is explained at some 
length. The image itself suffers change on turning 
back from the mirror. 
As when the plastic mask of wax, or clay, 
Dashed sudden ’gainst a wall, backward reverts, 
The well-recognized law that the angle of reflection is 
equal to the angle of incidence comes from Lucretius 
thus: 
