Ivii 



" At one time I had hoped that I had altered one coloured ray into 

 another by means of gold, which would have been equivalent to a change in 

 the number of undulations ; and though I have not confirmed that result as 

 yet, still those I have obtained seem to me to present a useful experi- 

 mental entrance into certain physical investigations respecting the nature 

 and action of a ray of light. I do not pretend that they are of great value 

 in their present state, but they are very suggestive, and they may save 

 much trouble to any experimentalist inclined to pursue and extend this line 

 of investigation." 



He gave two Friday discourses, the first on certain magnetic actions and 

 affections; and the second on M. Petitjean's process for silvering glass, 

 and some observations on divided gold. 



He gave five reports to the Trinity House, and he entered into an en- 

 gagement regarding the Board of Trade Lighthouses, and made four re- 

 ports, two on Cape Race Lighthouse, and one on Dr. Normandy's distilled 

 water-apparatus. 



He was made Corresponding Member of the Netherland Society of Sci- 

 • euces, Batavia, and Member of the Imperial Royal Institute of Padua. 



JEt. 65 (1857). 



Two Friday discourses were given, the first on the Conservation of Force, 

 and the second on the relations of Gold to Light. 



" Various circumstances," he begins, " induce me at the present moment 

 to put forth a consideration regarding the conservation of force. 

 . . . . There is no question which lies closer to the root of all 

 physical knowledge than that which inquires whether force can be de- 

 stroyed or not. ..... Agreeing with those who admit the con- 

 servation of force to be a principle in physics as large and sure as that of 

 the indestructibility of matter, or the invariability of gravity, I think that 

 no particular idea of force has a right to unlimited and unqualified accep- 

 tance that does not include assent to it. . . . Supposing the truth of 

 the principle is assented to, I come to its uses. No hypothesis should be 

 admitted nor any assertion of a fact credited that denies the principle. . . . 

 The received idea of gravity appears to me to ignore entirely the principle 

 of the conservation of force, and by the terms of its definition, if taken in 

 an absolute sense, ' varying inversely as the square of the distance,' to be 

 in direct opposition to it." 



To Mr. Barlow he writes : — 



" I am in town, and at work more or less every day. My memory 

 wearies me greatly in working ; for I cannot remember from day to day the 

 conclusions I come to, and all has to be thought out many times over. To 

 write it down gives no assistance, for what is written down, is itself for- 

 gotten. It is only by very slow degrees that this state of mental muddi- 

 ness can be wrought either through or under ; nevertheless I know that to 

 work somewhat, is far better than to stand still, even if nothing comes of it. 



