76 Anniversary Address by Lord Rayleigh.  [Nov. 30, 
millionth part. When we reflect upon the almost ultra microscopic magni- 
tude of a wave-length of light, the possibility of such an achievement may 
well excite our astonishment. 
For the advancement of science the main requirement is, of course, original 
work of a high standard, adequately explained and published. But this is 
not enough. The advances so made must be secured, and this can hardly be, 
unless they are appreciated by the scientific public. In some branches of 
pure Mathematics it is said that readers are scarcer than writers. At any 
rate the history of science shows that important original work is liable to be 
overlooked and is, perhaps the more hable, the higher the degree of originality. 
The names of T. Young, Mayer, Carnot, Waterston, and B. Stewart, will 
suggest themselves to the physicist ; and in other branches, doubtless, similar 
lists might be made of workers whose labours remained neglected for a shorter 
or a longer time. In looking into the more recent progress of Geometrical 
Optics, I have been astonished to find how little correlation there has been 
between the more important writings. That Coddington should have 
remained unknown in Germany and von Seidel in England need not greatly 
surprise us; but in this subject it would appear that a man cannot succeed in 
making even his own countrymen attend to him. Coddington seems to have 
heard nothing of Cotes and Smith, and Hamilton nothing of Airy and 
Coddington. 
It is true that no two writers on theoretical subjects could differ more in 
taste and style than do Hamilton and Coddington. The latter addressed 
himself to special problems, the solution of which seemed to have practical 
importance. Among his achievements was the rule relating to the curvature 
of images, generally known as Petzval’s, although Petzval’s work was of 
much later date. Hamilton, on the other hand, allowed his love of generality 
and of analytical developments to run away with him. In his Memoir on 
Systems of Rays, with its elaborate and rambling supplements, there is little 
to interest the practical optician, though the mark of genius is throughout 
apparent. It was only in two or three pages of a later paper that he applied 
his powerful methods to the real problem of Optics. As Finsterwalder 
has remarked, his “ six radical constants of aberration,” expressing the general 
properties of a symmetrical instrument, are at once an anticipation and a 
generalisation of von Seidel’s theorems. But the published work is the barest 
possible summary. If Hamilton had been endowed with any instinct for 
Optics proper, he could nave developed these results into a treatise of first-class 
importance. In more recent times Hamilton’s footsteps have been followed 
by Maxwell as well as by Thiesen and Bruns, of whom the two latter do not 
seein to have realised that Hamilton (or even Maxwell) had concerned himself 
