264 Scientific Intelligence. 



The red aud blue solutions of cobalt do not greatly differ in their spectra, 

 and the same is the case with the green and blue salts of copper. The 

 ammonical salts of copper give however a very different prismatic ap- 

 pearance. All the salts of sesquioxyd of iron absorb the more refrangi- 

 ble rays, leaving the least refrangible to penetrate almost any thickness. 

 The chromates exhibit a remarkable analogy in their spectra though 

 sometimes very different to the eye, but there is a wide diflference between 

 the compounds of sesquioxyd of chromium and chromic acid. The gen- 

 eral law laid down by the author is shown remarkably in the colors of 

 litmus, the neutral acid and alkaline solutions of this substance yielding 

 spectra which are only modifications of a common type. In compounds 

 of two colored bodies the chromatic effect of the components persists so 

 that it is often difficult to determine whether two bodies have combined 

 or not. The author draws the following conclusions as of value in analy- 

 sis. From the fact of the transmission of a particular ray we may infer 

 that none of those bodies which usually absorb that ray are present in 

 any kind of combination. The employment of the wedge and prism 

 will often present some familiar spectral appearance which is at once dis- 

 tinctive, although the unassisted eye cannot determine the source of the 

 color. The author in conclusion suggests that when a systematic com- 

 parison of different spectra shall have been made and regular tables of 

 comparison constructed, the prism will take its place among the recog- 

 nized instruments of the laboratory.— <2«<^^^^^y Journal of tJie Chemical 

 Society, x, 79. w, g. 



4, On the Disposition of Force in Paramagnetic and Diaraagnetic 

 Bodies ; by Professor Tvndall, F.R.S. (Proc. Roy. Inst, of Great Britain, 

 vol. ii, p. 159). — The notion of an attractive force, which draws bodies 

 towards the centre of the earth, was entertained hy Anaxagoras and h]S 

 pupils, by Democritus, Pythagoras, and Epicurus ; and the conjectures of 

 these ancients were renewed by Galileo, Huyghens, and others, who stated 

 that bodies attract each other as a magnet attracts iron. Kepler apphed 

 the notion to bodies beyond the surface of the earth, and affirmed the 

 extension of this force to the most distant stars. Thus it would appear, 

 that in the attraction of iron by a magnet originated the conception or 

 the force of gravitation. Nevertheless, if w^e look closely at the matter, 

 it will be seen that the magnetic force possesses characters strikingly dis- 

 tinct from those of the force which holds the universe together. The 

 theory of gravitation is, that every particle of matter attracts every other 

 particle ; in magnetism also we have the phenomenon of attraction, but 

 y^e have also, at the same time, the fact of repulsion, and the final effect 

 is always due to the dificrence of these two forces. A body may be in- 

 tensely acted on by a magnet, and still no motion of translation will fol- 

 low, if the repulsion be equal to the attraction. A dipping needle wa.s 

 exhibited : previous to magnetization, the needle, when its centre ot 

 gravity was supported, stood accurately level ; but, after magnetization, 

 one end of it was pulled towards the north pole of the eartli- The nee- 

 dle, however, being suspended from the arm of a fine balance, it was 

 shown that its wciffht was unaltered by its magnetization. In like man- 

 ner, when the needle was permitted to float upon a liquid, and thus to 

 follow the attraction of the north magnetic pole of the earth, there "vvas 



