7 1) Intelligence and Miscellaneous Articles. 



Proceeding thus, I have obtained, as the mean o£ a number of 

 determinations, the number 2*79 milligrams for the value of/. On 

 the contrary, measuring the superficial tension by employing the 

 drop-counter, I obtained the value 3'47 milligr., considerably higher 

 than the preceding. This difference, which surprised me at tirst, 

 too great to be attributed to errors of experiment, would need to 

 be controlled by other similar determinations made upon other 

 liquids, of which there are but few capable of forming films of large 

 extent. It may have been due, according to M. Duclaux (to whom 

 I submitted the difficulty), to the circumstance that in a very thin 

 film like that of soap-solution, the superficial tension has a lower 

 value than in the free surface of the same liquid in indefinite mass 

 — which would indicate that the thickness of the liquid layer in 

 which the molecules have the abnormal arrangement which produces 

 superficial tension exceeds half the thickness of the soap-film. 



Thanks to the same arrangement, I have been able to execute 

 other experiments suitable for showing the superficial tension of 

 liquids. Moreover, on replacing, in Plateau's polyhedra (such as the 

 tetrahedron, the cube, the octahedron, <fcc), a certain number of 

 rigid rods by flexible threads, we can produce with great facility, 

 and with a minimum quantity of liquid, laminar systems of consi- 

 derable dimensions and a certain number of surfaces possessing the 

 characteristic property that their mean curvature is nil. — Comptes 

 Hendus de VAcademie des Sciences, April 29, 1878, tome lxxxvi. 

 pp. 1057, 1058. 



ON THE MAGNETIC ROTATION OF THE PLANE OF POLARIZATION 

 OF LIGHT UNDER THE INFLUENCE OF THE EARTH. BY HENRI 

 BECQUEREL. 



In the course of my investigations on magnetic rotatory polari- 

 zation, I have been led to the direct estimation of the action of ter- 

 restrial magnetism upon various substances. This action can be 

 very neatly made evident by an experiment which seemed to me 

 sufficiently interesting to be communicated to the Academy. 



Between a Jellet polarizer and an analyzer furnished with a tele- 

 scope and mounted on a divided circle is placed a tube of half a 

 metre length, terminated by parallel glass plates and containing 

 bisulphide of carbon. At the two ends of the tube, plane mirrors 

 arranged as Faraday arranged them gave several successive reflec- 

 tions of the luminous ray, and thus augmented the observed rota- 

 tion. In the present experiment the second reflection could be 

 viewed ; the ray had therefore traversed the tube five times, corre- 

 sponding to a thickness of 2-b metres of bisulphide of carbon. The 

 source of light was a pipe with oxyhydrogen gas. A great amount 

 of light was lost by absorption and by the successive reflections; 

 and the rays transmitted to the eye were chiefly the yellow rays. 

 The entire system was firmly fixed to a horizontal copper rule, and 



