Fig. 3.
Fig. 4.
This arrangement, which is adopted in Mr. Kapp's instruments, gives very good results, as may be easily seen by reference to Figs. 3 and 4, in which the current intensities or differences of potential are referred as ordinates and the degrees of deflection of the needle as abscissas. The unbroken lines represent the curves obtained with the apparatus just described, while the dotted ones give the curve of deflection of an ordinary tangent galvanometer. These curves show that for strong intensities of current Mr. Kapp's instrument is more advantageous than the tangent galvanometer. Mr. Crompton has constructed an amperemeter upon the same principle, which is shown in Fig. 5.—La Lumiere Electrique.
Fig. 5.
THE CHEMICAL ACTION OF LIGHT.
Professor A. Vogel, in a communication to the "Sitzungsberichte der Munchener Akademie," brings into prominence the fact that the hemlock plant, which yields coniine in Bavaria, contains none in Scotland. Hence he concludes that solar light plays a part in the generation of the alkaloids in plants. This view is corroborated by the circumstance that the tropical cinchonas, if cultivated in our feebly lighted hothouses, yield scarcely any alkaloids. Prof. Vogel has proved this experimentally. He has examined the barks of cinchona plants obtained from different conservatories, but has not found in any of them the characteristic reaction of quinine. Of course it is still possible that quinine might be discovered in other conservatory-grown cinchonas, especially as the specimens operated upon were not fully developed. But as the reaction employed indicates very small quantities of quinine, it may be safely assumed that the barks examined contained not a trace of this alkaloid, and it can scarcely be doubted that the deficiency of sunlight in our hothouses is one of the causes of the deficiency of quinine.