Natural-PhUosopkical Collections. 385 



well as M. Brongniart complain that this opinion has been laid to their charge. 

 The latter considers motion as inherent in these molecules ; and Mr. Brown de- 

 clares, that the extremely divided particles of a solid body, when they are sus- 

 pended in pure water, or in any other aqueous fluid, show motions for which, he 

 says, he cannot account, and which, from their irregularity and apparent inde- 

 pendence, resemble, in a remarkable degree, the less rapid motions of some of the 

 most simple of the inferior animals. Mr. Brown had, in his first paper, stated 

 that the granules in motion were spherical, of an uniform diameter, although he 

 had seen them varying from 1-15 thousandth to 1-20 thousandth of an English 

 inch, according to the different substances submitted to examination. Now he says 

 that these molecules, which he calls active, appear to be spherical or nearly so, and 

 have a diameter of fVom 1-20 thousandth to 1-30 thousandth of an English inch, 

 and that other particles of a considerably larger and diversified volume, and of a 

 form either similar or very different, also present similar motions in the same cir- 

 cumstances. The author could not make broader concessions for our refutation. 

 On the subject of forms and volumes it is precisely what we opposed to the first 

 epinion of the learned members of the two French and English academies. 



The causes to which we have attiibuted the different motions described by 

 these gentlemen, have no doubt appeared so clearly established to Mr. Brown, that, 

 80 far from seeking in the least to refvite our opinion, he has laid aside all his 

 first experiments, and has had recourse to a new one, which, according to the 

 author, is of itself sufficient to prove the reality of these motions, which are no 

 longer spontaneous. 



Mr. Brown, wishing to set aside the external causes to which these motions 

 were attributed by those who do not admit this property as inherent in matter, 

 has devised a precaution which M. Ad. de Jussieu has forthwith found to be 

 fimple and ingenious. This precaution consists in immersing the droplet of wa- 

 ter which contains the particles under observation in a drop of a fluid specifically 

 lighter, with which it cannot mingle, and whose evaporation is extremely slow, 

 almond oil for example. The two fluids are agitated together. The drop of 

 water d'vides into several others of unequal size, which are, as it were, imprison* 

 edin the oil. Evaporation is thus suspended, and the formation of currents which 

 resnk from it is suspended, as well as the disengagement of gas ; yet the motion 

 of the particles continues with the same activity. There may thus be obtained 

 droplets which contain only a single particle, and its motion, which continues to 

 take place, cannot then be attributed to a reciprocal action. So says Mr. Brown ; 

 and thus all the other experiments are good for nothing. All the motions of 

 which they give evidence may be then attributed to external influences. Mr. 

 Brown had therefore blundered at first ; and if such motions exist, it is now only 

 that he proves their existence. But yet, at the risk of being accused by the edi- 

 tors of the Arinales des Sciences Naturelles, of professing a snappish incredulity, 

 we declare explicitly that of all the experiments of Messrs. Brongniart and Brown, 

 this is the most defective and most unpardonable ; and for these reasons, whidi 

 no doubt Mr. Brown will at the same period of next year do us the honour of re- 

 Riting: 1st, The agitation impressed upon these different droplets does not 

 cease promptly, and the motion still continues after the fugitive moment of a mi- 

 croscopic examination % 2dly, The aqueous droplets suspended in the oil are not 

 withdrawn from the laws of attraction or capillarity, but are seen coming together 

 and rapidly xmiting ; 3dly, The drops of water, being heavier than the oil, tend 

 to fall towards the bottom of the capsule ; 4th]y, By the very fact of their suspen- 

 sion in fluid, they must be subject to the motions impressed upon this fluid mass 

 by the agitation of the air, the more or less sensible shaking of the place, and 

 the breath of the observer. All these indisputable causes of motion, althou^ 

 Mr. Brown has not foreseen them, cannot take place without the single molecule 

 which the droplet of water contains, changing its position with relation to the eye 

 af the observer, and without its seeming to direct itsdf downwards, or horizontally, 

 et upon -an inclined plane. 



