Biographical Memoir of Dr Thomas Young. 225 



without scruple, then, attached to the plaything of a child, the 

 discovery which I am about to analyze, with the assurance that 

 it will not suffer from its connection with this origin. At all 

 events, I have no occasion to call to recollection, either the ap- 

 ple which, leaving the branch on which it grew, and falling un- 

 expectedly at the feet of Newton, directed the thoughts of this 

 great man to the simple but pregnant laws which regulate the 

 movements of the stars ; nor to the divided frog to which 

 Physics has been recently so much indebted in the wondrous 

 pile of Volta. In truth, without even pronouncing the name of 

 soap-bubbles, I might have supposed that a philosopher had 

 chosen for the subject of his experiments distilled water, that is 

 to say, a liquid which, in its pure state, exhibits only the slight- 

 est tints of blue and green, and then only when seen in thick 

 masses. What then, would have been the thought of his vera- 

 city, if he announced, without any further explanation, that 

 to this limpid water he could, at will, communicate the most 

 resplendent colours ; that he knew how to make it violet, blue 

 and green ; that he knew how to make it yellow like lemon-peel, 

 and red like scarlet, without altering its purity, or mixing it 

 with any foreign body, or even without changing the propor- 

 tions of its principal gaseous constituents ? The public would 

 assuredly consider the philosopher unworthy of all credit when, 

 after so many strange propositions, he should moreover add, that, 

 to produce the colour in the water, all that was necessary was 

 to reduce it to the state of a thin pellicle ; and that thinness 

 may thus be regarded as synonymous with coloured; that the 

 transition of each tint to a tint the most different is a necessary 

 consequence of a simple variation of the thickness of the liquid 

 lamina ; and that this variation, in the transition of the red to 

 the green ray, for example, is not more than the thousandth 

 part of the thickness of a hair ! Well then, these incredible 

 theorems are nothing more than the inevitable consequences of 

 the properties of the colouring which are presented by the soap- 

 bubbles, and even by the very thin laminae of all kinds of 

 bodies. 



That we may comprehend how such extraordinary pheno- 

 mena have, for more than two thousand years, daily presented 

 themselves to the eyes of philosophers, without exciting their at. 



