550 Intelligence and Miscellaneous Articles \ 



of union ; the attractions of very close -lying parts enter into it evi- 

 dently in great measure. 



When a simple substance unites with another element, the force 

 of union is not always attractive ; and thus we have an explanation of 

 facts hitherto difficult to understand — for instance, the heat produced 

 by the decomposition of binoxide of nitrogen. The atoms of oxy- 

 gen and those of nitrogen attract at distances greater than e with a 

 force (universal gravity) which is only appreciable for large masses. 

 At distances less than a certain quantity e', very small as compared 

 with e, they still attract; but in the interval ee' they repel one an- 

 other, and the work of chemical union consists of one part negative 

 and one part positive which is less. They do not combine directly, 

 because they repel one another ; but when by any means they are 

 made to traverse the interval e e\ they may remain united. These 

 latter views are partly hypothetical ; hence we shall not fail to sub- 

 mit them to all the verifications of which they are capable. The 

 principal difficulties arise from the circumstance that chemical pro- 

 ducts must be used which are very pure, and capable of furnishing 

 the best determinations. With ternary compounds, if the choice is 

 not good, the errors to be feared accumulate very rapidly in the cal- 

 culation. 



We have shown, by the known values of the forces of union and 

 attraction on contact, that the general law of attraction would not 

 be expressed by several terms obtained by multiplying whole powers 

 of the inverse of the distance by constant coefficients. It would 

 appear to be represented by the sum of three functions of the dis- 

 tance, of which the first (that is, the astronomical function) would pre- 

 dominate completely at great distances, and could be entirely neg- 

 lected at small ones. The second, which might be called the phy- 

 sical function, would predominate in the interval e e'\ it would almost 

 completely determine the force of union, and would be common to 

 all simple substances, provided it were preceded hy the inverse of the 

 equivalent as a factor. The third, finally^(that is, the chemical func- 

 tion), would predominate in turn from zero to e' . — Comptes Rendus, 

 April 2, 1866. \ 



ON A NEW METHOD OF MEASURING THE LENGTHS OF LUMINOUS 

 WAVES. BY PROF. STEFAN. 



If light be allowed to fall on a column of quartz with polished 

 faces parallel to the optic axis, each ray is resolved into the ordinary 

 and the extraordinary ray, if the faces of entrance and of emergence 

 are parallel. If both are again brought into a common direction of 

 vibration, all those rays are extinguished the difference of whose 

 path amounts to an uneven number of semi-wavelengths. If the 

 spectrum of the light is formed, dark interference- bands appear, 

 which are the more numerous and the finer the thicker the quartz. 

 The difference of phase between two rays may be calculated from 

 the thickness of the quartz, and from the quotients of refraction, — 

 and with great accuracy, since only the differences, and not the ab- 

 solute values of the latter are required. Twice the difference of 

 phase divided by the wave-length is an uneven number for each 

 dark band, and for each succeeding one towards violet is two units 



