432 Prof. G. Yan der Mensbrugghe on a new Application 



There remain two objections to oppose to Sir B. C. Brodie; 

 but they are of less importance. The first is that Sir B. C. 

 Brodie admits, without any experimental proof, the compound 

 nature of certain bodies considered simple, like chlorine and 

 potassium, while others, like mercury, remain simple — although 

 it appears, according to the law of Dulong and Petit, that all 

 our elements ought to be compound, or none of them ought 

 to be compound, at least of those to which the law of Dulong 

 and Petit is applicable. We repeat, however, that though 

 Lockyer's experiences do not conclusively establish the com- 

 pound nature of our elements, this would be one step towards 

 the verification of Sir B. C. Brodie's hypothesis. 



The second objection is that the law of even numbers, which 

 serves as the basis of the new notation, can be thoroughly 

 established in the series of carbon combinations, but it cannot 

 be so completely established in the other series. It would 

 perhaps be simpler to admit that this law is not universal 

 than to admit that chlorine and nitrogen are compound bodies. 

 In any case we cannot do better than repeat, in conclusion, 

 that which we have already said. All hypotheses are but 

 mental artifices to guide us to the discovery of truth; and 

 since a new hypothesis opens new horizons to the investigator, 

 this hypothesis may be fruitful, and ought to be accepted, 

 either by replacing an old hypothesis which has become ste- 

 rile, or by concurrence with it. It is for this reason that we 

 have translated Sir B. C. Brodie's memoirs; it is for this 

 reason that we do not understand indifference towards his 

 work, and that we should understand such indifference still 

 less now that he has done away with one of the two principal 

 difficulties which we thought we had found in his system, and 

 that he promises before long to do away with the second. 



LXVI. On a neiv Application of the Potential Energy of Liquid 

 Surfaces. By Professor Gr. Van dee Mensbrugghe*. 



IN a recent memoirf I sought to confirm my theory of the 

 variations of potential energy of liquid surfaces by pre- 

 senting a series of proofs drawn from the observation of liquid 

 films either with two free faces or spread upon another liquid. 

 I had hardly finished the writing of that memoir when my 

 attention was drawn to the remarkable phenomena presented 



* Translated from a separate impression communicated by the Author, 

 from the Bulletins de V AcademieBoyale de Belgique, 2 e serie.t. xlvi. no. 11, 

 1878. , 



t " Etudes sur les variations d'energie potentielle des surfaces liquides," 

 Mem. de VAcad. royale de Belgique, 1878, t. xliii. 



