224 Intelligence and Miscellaneous Articles. 



and with the second the sensation of green to a higher degree than 

 is done by the sight of the green itself. 



This blue, however, still does not represent the sensation of that 

 colour in its greatest intensity, since a better is obtained by min- 

 gling the sensations of the fourth green and the third blue. The 

 orange, the second or third green-yellow, and the third blue are 

 therefore three points of the chromatic circle which possess for our 

 eye peculiar properties, since they permit the reproduction, by the 

 mixture of their sensations, of the most intense red, green, and blue. 



These three colours possess the properties of the fundamental 

 sensations of Young. But can they really be regarded as repre- 

 senting exactly those three points ? The theory of Young is only 

 an hypothesis ; and physicists have not come to a determination 

 upon the true position of these three sensations. The uncertainty 

 which prevails on the question causes Helmholtz* to say : — " The 

 choice of the fundamental sensations presents at first something 

 arbitrary. One might choose at pleasure three colours whose mix- 

 ture produces white There does not yet exist, to my know- 

 ledge, any means of determining the fundamental colours but the 

 examination of persons affected with dyschromatopsy." 



I purpose to demonstrate, in a second Note, that, on the con- 

 trary, the colours in question are situated in the chromatid circle 

 between very narrow limits, and that the three maxima obtained by 

 the study of which I have here given a summary are in reality the 

 colours corresponding to the fundamental sensations. — Comptes 

 Rendus de V Academic des Sciences, t. xcii. pp. 244-247, Jan. 31, 1881. 



ON THE LIBERATION OF ELECTRICITY IN TOURMALINE BY 

 PRESSURE. BY MM. JACQUES AND PIERRE CURIE. 

 "We will at once enunciate the laws which follow from our experi- 

 ments on the liberation of electricity in tourmaline by pressure. "We 

 will afterwards explain, with the rapidity required by the brevity 

 of this Note, our experimental processes and the limits within which 

 we have verified those laws. 



I. The two extremities of a tourmaline liberate electricity of oppo- 

 site signs, in quantities equal to one another. 



II. The amount set free by a certain augmentation of pressure is of 

 opposite sign, and equal, to that 'produced by an equal diminution of 



pressure. 



III. This quantity is proportional to the alteration of pressure. 

 IY. It is independent of the length of the tourmaline. 



Y. For one and the same alteration of pressure per unit of surface, 

 it is proportional to the surface. 



The direct result of the experiments from which laws IY. and 

 Y. are deduced can be stated in a simple manner thus : — For 

 one and the same alteration of pressure, the quantity of electricity set 

 free is independent of the dimensions of the tourmaline. 



The tourmalines which we wished to study had the form of prisms 

 parallel to the principal axis. The two bases were covered with two 

 sheets of tin foil protected outside by two thick plates of glass, 

 * Opti^ue Physiohgique, p. 384. 



