the flame or a weak spark, totally disappear at the higher temperature. The new bright lines, which supply the part of the broad bands, are generally not coincident with any part of the band, sometimes being less and sometimes being more refrangible. The gentlemen who made these experiments add, that possibly the cause of the disappearance of the broad bands and the production of the bright lines may be, that at the lower temperature of the flame or weak spark, the spectrum observed is produced by the glowing vapour of some compound, probably the oxide of the difficultly reducible metal, whereas, at the enormously high temperature of the intense electric spark, these compounds are split up, and the true spectrum is obtained, namely, the narrow bright lines. No such changes take place in the easily reducible metals, potassium, sodium, or lithium, which remain unaltered by change of temperature. In these experiments, a bead of the metallic salt on a platinum wire was placed between the platinum terminals, from which the spark of a powerful inductive coil could be passed, but in order to have a more intensely hot spark the coating of a Leyden jar was placed in communication with the terminals of the secondary current respectively. By this addition of static electricity, the intensity of the current was increased four-fold, and must have been beyond estimation. By high temperature the cæsium spectrum has been so changed, that for number, colour and distinctness of its lines, it is the most beautiful of those of the alkaline and earthy metals, for besides its characteristic blue lines, it has six red and an orange-red line in the red part of its spectrum, a fine yellow line, and nine green lines, the last coinciding with Fraunhofer’s E. The thallium spectrum also acquires more lines when evaporated by electricity, for besides the remarkable green line in the green, it acquires a faint one in the orange, two of nearly equal intensity in the green, a third fainter, and a fifth in the blue. MM. Plücker and Hittorf, in recent experiments, proved that many non-metallic bodies, such as nitrogen and sulphur, give two distinctly different spectra on change of temperature, and that the transition from one spectrum to the other is sudden. The change is particularly striking in sulphur, for at the moment the first spectrum attains its maximum brightness, it disappears, and gives place to the second or high temperature spectrum, which is one of the richest in brilliant rays known. When the temperature is lowered the first spectrum reappears. These changes M. Plücker ascribes to the existence of the elements in two allotropic conditions. M. Plücker has also found that each metalloid possesses a peculiar and characteristic spectrum: as hydrogen, which has three bright lines, all of which are coincident with dark solar lines, and nitrogen, which exhibits a complicated series of bands.