366 Scientific Intelligence. 



which M. Ruppell speaks. If M. Ruppell first saw the star near the mar- 

 gin of the field, and afterwards saw it near the middle of it, the explana- 

 tion would be easy; but it is necessary to suppose that the distinctness in 

 question arose from the proximity of the star to the moon. It is by no 

 means impossible that the dispersion produced by the lunar atmosphere 

 might correct the uncorrected colour in the telescope, if such uncorrect- 

 ed colour existed. 



8. Remarkable Dichroi.ini of Axinite. — The dichroism of this mineral 

 has already been observed, and mentioned in the Philosophical Transac- 

 tions for 1819, p. 20 ; but Mr Haidinger has observed in Mr Allan's Col- 

 lection a crystal from Cornwall, in which it is very remarkable, and he got 

 it cut for the purpose of exhibiting it to advantage. By looking through 

 the faces ?■?•' of the figures of Axinite in Hauy and Mohs, there is aline in- 

 clined towards the face t, where common light transmitted through the plate 

 is a minimum, and of a dark red colour, but not polarised, or rather consist- 

 ing of two superimposed pencils polarised in opposite planes. By continuing 

 the inclination towards i, the light becomes brighter and whiter, and all 

 polarised in one plane, as if transmitted through a bundle of glass plates. 

 By inclining the plate in the opposite direction towards x, the very same ef- 

 fect is produced. These effects are obviously owing to the absorption of 

 one of the pencils by the crystal, as described in the Article Optics, of the 

 Edinburgh Encyclopaedia, Vol. XV. p. 601. 



9. Optical Structure of Somervillite. — This interesting mineral species, 

 which we have already described in this Journal, Vol. I. p. 187, has one 

 axis of double refraction, as it ought to have by the optical law of primi- 

 tive forms. The action of that axis upon light is negative, by the exa- 

 mination of the rings, and the double images, as it ought to be by another 

 optical law. The separation of the images is easily seen through the faces 

 P and a, in our Figure, Vol. I. Plate VIII. Fig. 4. Somervillite contains 

 several crystallised cavities, when examined by the microscope. For the 

 specimen with which we made the preceding observations, we have been 

 indebted to Dr Somerville, whose name it bears. 



MAGNETISM. 



10. Magnetic Variation at Lake Superior. — The following observations 

 have been made by Mr Thompson, astronomer to the Boundary Commis- 

 sion: 



W. Long. N. Lat. Easterly Variation. 



