THY. LIFE OF MATTKR. 409 



Mction of the lu'ighboriiio- particles. We ti|)pr():ich that coiKliiioii 

 when we observe through "the microscope grains of dust suspended in 

 a li(juid or g-lobules of oil suspended in water. Now the result of 

 this case is well known to all niicroscopists. If the granulations are 

 sufficientl}' small, they are seen to be never at rest. Thev are 

 animated l)v a sort of incessant tremor; we see the phenomenon 

 cidlcHl the "'Brownian movement."" The spectacle of this agitation 

 has sti'uck all ol)servers since the invention of the loupe or simple 

 microscope. But the Englishman, Hrt)\vn, in 18:^7, made it the object 

 of a special study and left it his name. The exact explanation of it 

 remained for a long time obscui'e. It was given in 1S',I4 ]>y the learned 

 ph3'sicist of the faculty of Lyons, M. Uouy. 



The observer who for the first time looks through the microscope 

 at a drop of water from the river, from the sea, or from any ordinary 

 source — that is to say, water not specially puritied — is struck with sur- 

 prise and admiration at the spectacle of the motion that appears in it. 

 Infusoria, microscopic articulata, various micro-organisms, people the 

 microscopic tield and animate it with their movements; but at the 

 same time all soi'ts of particles are also agitated, particles which can 

 not be considered as living beings and which are, in fact, nothing but 

 organic detritus, mineral dust and debris of every description, (^uite 

 often the singular movements of these g"ranulations, w^hich sinndate up 

 to a certain ])oint those of living- beings, have perplex(Kl the observer 

 or drawn him into error, and the bodies that manifest them ha\'e Ixmmi 

 taken for animalcules or for l)acteria. 



Charactei'K of thh inot'einent. — But it is ordinarily quite easy to 

 avoid this confusion. The Brownian movement is a sort of oscillation, 

 a treadmill of to and fro movement not accompanied by translation. 

 It is a Saint Guy's dance executed in one spot, thus distinguished from 

 the movements of displacement habitual to animate beings. Each 

 particle executes its own special dance. Each one acts on its own 

 account independently of its neighbor. Theri^ is, however, in the 

 execution of these individual oscillations a sort of connnon and regular 

 character which arises from the fact that their amplitudes ditiei- little 

 from each other, Th(> largest particles are the slowest; alK)\'e four 

 one-thousandths of a millimeter in diameter they almost cease to be 

 mobile. The smallest are most active. WhiMi so small as to be barelv 

 visible througi) the microscope the mo\ ement is extremely rapid and 

 can only occasionally be perceived. It is proba])l(^ that it would be 

 still more accelerated for smaller ot)j(H-ts. but the latter ai-e destined 

 to eternally escape our observation. 



Its iiid('ju'ii<hnc(' of tin' )t(ifin'(' (ftJir Jxid'us oiid <f the eiirlroiniKiif. — 

 M. Gouy has remarked that the movement depends neither on the 

 nature nor on. the form of the j)articles. Even the nature of th(> 

 liquid has but little intluence. Its degree of viscosity aloiu^ is of etle(!t. 



