Intelligence and Miscellaneous Articles, 235 



tating mirror. From the upper point of the flame to the spark, the 

 image in the mirror appears to have serrate incisions, and at the 

 lower point of each dark incision there is a passing spark. During this 

 transition of an individual spark, the flame, therefore, is always extin- 

 guished above. The part below the spark is constant and steady. 



The reason of this extinction of the upper part of the flame by the 

 spark is due to the fact that the spark causes a very rapid combus- 

 tion of the gases on its path, and then by the mechanical pressure 

 which the spark thereby exercises on all sides, the access of gas 

 from below is prevented for a moment. 



The extinction of the upper flame at each spark which passes is 

 also seen by another mode of investigation, in the following manner: — 



While the sparks pass through the flame, and in such a manner 

 that the latter is apparently quite steady, it is viewed through a rota- 

 ting disk in which there are several narrow slits. Viewed at right 

 angles to the direction of the passing spark, the flame above the 

 spark seems formed of bright and dark layers ; viewed in the direction 

 of the spark, layers in the proper sense are not seen, but dark circles 

 rather continuously rising on the flame. It is best for the latter ob- 

 servation if one electrode is in the flame, the other remaining out- 

 side, and this latter is looked at from the side. 



It is not necessary here to explain minutely in what manner this 

 production of bright and dark lines by the cooperation of the alter- 

 nating flame and momentary observation is brought about. The 

 phenomenon depends essentially on the same principle as that on 

 which an emerging jet of water, when looked at through a rotating 

 disk, seems formed of individual drops. It is clear that the number 

 and motion of the dark and bright layers of the flame alter with the 

 number of slits of the rotating disk, and with the velocity of rota- 

 tion. — Poggendorff's Annalen, May 1866. 



ON 



DUCTION OF TEMPERATURE. BY DR. E. LINDIG OE SCHWERIN. 



As the physical processes in the so-called supersaturation of 

 Glauber's salt solutions have as yet found no sufficient explanation, 

 either from physicists or chemists, it will not be uninteresting if I 

 communicate a few observations on this subject. 



If a solution of Glauber's salt, whether saturated or not, is allowed 

 to cool slowly, it contracts with diminution of temperature, like any 

 other body, as long as there is no crystallization. But as soon as 

 the first crystals form in the clear solution, instead of contracting, it 

 begins to expand, and continues to do so in proportion as the crys- 

 tallization proceeds. Hence the density of the crystals forming is 

 less than that of the solution from which they form*. 



Surprising as is this deportment of a gradually crystallizing solu- 

 tion of Glauber's salt, that of a so-called supersaturated solution is 



* With this the circumstance seems to disagree, that detached crystals 

 did not swim in the liquid, but sank to the bottom. 



