1814.] Scientific Intelligence. 467 



the perpendicular incidence of the influence of this last axis it is 

 null. Considering the simultaneous action of these two forces 

 when the plate is inclined, he deduces from them all the complex 

 phenomena which the mica presents under different inclinations. 



To confirm this theory by a striking proof, he assembles plates of 

 sulphate of lime and of rock crystal, so as to imitate tlie systems of 

 forces which he has discovered in mica. Tlie resulting phenomena 

 are absolutely the same with those exhibited by the mica. 



In another memoir, M. Biot dc;duces from his theory the con- 

 stancy of the colours which plates of sulphate of lime exhibit 

 under all incidences when they are inclined upon a polarized ray, 

 so that their axis of crystallization makes an angle of 45° with the 

 plane of incidence. He show.^ also, by calculation, on what the 

 change of colour depends, which takes' place when it is removed 

 from that position, and in what order it ought to take place accord- 

 ing to the different movements given to the plate. 



Hitherto all the experiments of M. Biot, as well as the theory 

 deduced from them, apply only to the cases in which the double 

 refraction is very weak. However, in a memoir read this summer 

 to the Society of Arcueil, he proved that the extraordinary refracting 

 force of Iceland crystal acts upon the different luminous molecules 

 in the same order as that of other crystals. And he has been able 

 to ascertain from theory how it is necessary to proceed, in order to 

 attenuate the repulsive force of Iceland crystal, so as to make it 

 produce the phenomena of colours similar to those of other crys- 

 tallized bodies that he had observed. He has succeeded in the 

 same way with arragonite, the double refraction of which is also 

 very strong. Further, by crossing these two substances with plates / 

 of sulphate of lime, he has produced colours under all incidences, 

 and in circumstances when they were very far from giving them 

 naturally. This shows, that the luminous molecules commence 

 oscillating in them, as well as in other substances, before assuming 

 a fixed polarization. These results, which complete the theory at 

 the same time that they confirm it, constitute the object of the last 

 memoir read by JNI. Biot. 



(To he continued.) 



Article XII. 

 SCIENTIFIC intelligence; and notices of subjects 



CONNECTED WITH SCIENCE. 



I. Method of grndikating Glass Tubes. 



I PROMISED last .summer to give a description of my method of 

 graduating glass tubes ; but Imvc not hitherto been able to find 



2(i 2 



