620 PLATEAU ON FIQUBESOFEQUILIBRIUM OFALIQUID MASS. 



hollow ; the layers in pi-ogress of formation are plane, and 

 arranged symmetrically, so that the system tends towards the 

 form represented at fig. 20. But when a certain limit is attained, 

 a sudden change occurs, the layers become curved, and the 

 system tends to assume the singular form which we have men- 

 tioned. I have several times repeated the experiment, varying 

 the circumstances as much as possible, and the same effects are 

 always produced. 



In the course of this memoir, I shall point out another pro- 

 cess for obtaining laminar systems ; it is an extremely simple 

 one, and has moreover the advantage of producing all the sy- 

 stems in a complete state. 



36. In concluding our observations upon polyhedric liquids, 

 I shall remark that the triangular prism may be employed to pro- 

 duce the phaenomena of dispersion. In this way a beautiful solar 

 spectrum may be obtained by means of a prism with liquid faces. 

 But as the effect only depends upon the excess of the refracting 

 action of the oil above that of the alcoholic liquid, to obtain a 

 considerably extended spectrum the angle of refraction of the 

 prism must be obtuse ; an angle of 1 10° gives a very good result. 

 Moreover, it is evidently requisite that the faces of the prism 

 should be perfectly plane, which is obtained by using a carefully 

 made frame ; by establishing exact equilibrium between the 

 density of the liquids ; and lastly, by arresting the action of the 

 syringe exactly at the proper point. 



[To be continued.] 



