430 Scientific Intelligence. 



were more in harmony. In time a condition of stability would 

 be established, and we should have our present series of chemical 

 elements, each with a definite atomic weight — definite on account 

 of its being the average weight of an enormous number of sub- 

 atoms, or meta-elements, each very near to the mean. The 

 atomic weight of mercury, for instance, is called 200, but the 

 atom of mercury, as we know it, is assumed to be made up of an 

 enormous number of sub atoms, each of which may vary slightly 

 round the mean number 200 as a centre. 



We are sometimes asked why, if the elements have been 

 evolved, we never see one of them transformed, or in process of 

 transformation, into another. The question is as futile as the 

 cavil that in the organic world we never see a horse metamor- 

 phosed into a cow. Before copper, e. g., can be transmuted into 

 gold, it would have to be carried back to a simpler and more 

 primitive state of matter, and then, so to speak, shunted on to 

 the track which leads to gold. 



This atomic scheme postulates a to-and-fro motion of a form 

 of energy governing the electrical state of the atom. It is found 

 that those elements generated as they approach the central 

 position are electro-positive, and those on the retreat from this 

 position are electro- negative. Moreover, the degree of positive- 

 ness or negativeness depends on the distance of the element from 

 the central line; hence, calling the atom in the mean position 

 electrically neutral, those sub-atoms which are on one side of the 

 mean will be charged with positive electricity, and those on the 

 other side of the mean j3osition will be charged with negative 

 electricity, the whole atom being neutral. 



This is not a mere hypothesis, but may take the rank of a 

 theory. It has been experimentally verified as far as possible with 

 so baffling an enigma. Long-continued research in the laboratory 

 has shown that in matter which has responded to every test of 

 an element, there are minute shades of difference which have 

 admitted of selection and resolution into meta-elements, having 

 exactly the properties required by theory. The earth yttria, 

 which has been of such value in these electrical researches as a 

 test of negatively excited atoms, is of no less interest in chemistry, 

 having been the first body in which the existence of this sub- 

 group of meta-elements was demonstrated. 



10. Geschichte der Photographie ; by C. Schiendl. pp. 380, 

 small 4to, Vienna (Hartleben). — The author commences with a 

 brief review of what few observations were made by the ancients 

 upon the action of light, which seem to have amounted to very 

 little, and then passes to the early beginnings of photography in 

 modern times. These chapters are full of interest. From his in- 

 vestigations the author concludes that the first actual image pro- 

 duced by light was obtained by J. H. Schulze in 1727 who ob- 

 served that a mixture of nitric acid, silver nitrate and lime in ex- 

 cess produced a compound which darkened in sunlight but that 

 the portion under the piece of cord, which he tied around the flask 



