318 Scientific Intelligence, Sfc. 



3. No comets have presented hitherto any phases, so that we were 

 ignorant of the nature of the light of these bodies. It was expected 

 that the intensity would have been determined during the last 

 appearance of Halley's comet, but the remarkable changes which it 

 underwent prevented this from being effected. M. Arago, therefore, 

 adopted another method. On the 23rd October, having applied an 

 apparatus adapted for observation, he saw two images, which pre- 

 sented complementary tints, one red, the other green. By making 

 a half revolution of the telescope upon itself, the red image became 

 green, and vice versa. " Thus the light of the star, was not com- 

 pletely, at least, composed of rays endued with the properties of 

 direct light, peculiar or assimilated; it contained some light reflected 

 specularly or polarized, that is to say, definitely, some light proceed- 

 ing from the sun." 



VIII. — -Diamonds of the Uralian Mountains. 



Professor Engei,hardt, of Dorpat, from an examination of the 

 geological nature of these mountains some time ago, gave it as his 

 opinion, that they contained diamonds ; but Count Polie was the 

 first to discover them, during the travels of Humboldt in that country. 

 M. Parrot has examined 30 of these precious products of the mine, 

 which were formerly confined to India and Brazil. All of them 

 have 24 triangular faces, more or less irregular and mostly striated. 

 They belong to a kind of rhomboidal dodecahedron, of which each 

 rhomboid is here as it were folded up on the diagonal which passes 

 through the obtuse angles. Several of them have a yellow tinge. They 

 are all oblong and more or less flattened. Two of them, one weighing 

 \ carat, and the other §4 carat, contained small black bodies. They 

 are not crystallized, but may be compared to bodies in the form of 

 moss as in agates. They are not acted on by the magnet. Parrot 

 conceives, that as " chemical analysis has proved that the diamond 

 is composed almost entirely of carbon and a very little hydrogen like 

 vegetable carbon, it is Very probable, that the black matter of these 

 diamonds is a species of vegetable carbon, under an uncrystallized 

 form. It is well known also, that jewellers who receive diamonds 

 for cutting, deprive them of the black streaks which are frequently 

 attached to them externally by ignition, which would not happen if 

 these were not formed by a compound of carbon and hydrogen. This 

 observation on the exterior streaks which form a mass with the ex- 

 terior layers of the diamond, furnish us with a new analogy, for 

 admitting with a high degree of probability, that the black matter 

 of the two diamonds which we have examined, is a substance, con- 

 sisting of carbon and hydrogen, and that these diamonds themselves 

 are still imperfect diamonds. But what appears to decide the 

 question is, that the small black masses in the crystal which we exa- 

 mined are isolated and entirely enclosed in the crystalline mass, 

 without touching any of its faces or angles. If they were hetero- 

 geneous bodies, formed previous to crystallization, they would have 

 been placed upon some base and covered there with the crystalline 

 mass, as occurs, for example, in quartz, agates, &c, where the foreign 



