Intelligence and Miscellaneous Articles. 325 



obtained which possesses the property of fluorescence. In this state 

 the fluid is rather too concentrated, and in order to obtain the proper 

 degree of dilution I proceed in the following manner : — I take a 

 quadrangular glass vessel with parallel walls of about an inch and a 

 half in height, half-fill it with alcohol of the above strength, and 

 then add the fluid. By producing a cone of light in this by means 

 of a biconvex glass of short focus, the intensity of the colour will 

 soon show whether the right degree of dilution has been attained. 

 The fluorescence is greenish-blue, like that which is obtained by 

 means of an extract of the seeds of the thorn-apple. Its beliaviour 

 towards coloured glasses is also the same. If a brownish-yellow glass 

 be held between the eye and the fluorescent cone of light, the latter 

 is seen almost unaltered ; but it disappears almost entirely when the 

 glass disc is brought between the lens and the fluid. 



2. Relation of fluorescence to the electric light. — The luminous 

 phEenomena of electricity may evidently be divided into two classes ; 

 namely the phaenomena of the electric spark, and the luminosity 

 produced by the ignition of the bodies through which electricity- 

 passes. The former light may be produced by the sparks of the 

 machine, or still better, because stronger, by the induction apparatus 

 with Neef s arrangement. I have therefore operated with the latter 

 apparatus. The induction apparatus is connected with an electro- 

 meter in such a way, that the wire which touches the lead forms the 

 negative electrode. When the apparatus is in action, a blue light is 

 observed, covering the surface of the wire like a cloak. 



The following fluids were poured into test-tubes to a certain 

 height ; these were held at the height of the fluids to the electric 

 light, and looked into from above : — 1. A solution of sulphate 

 of quinine in water. 2. A decoction of the bark of the horse- 

 chestnut. 3. An alcoholic extract of the seeds of the thorn-apple. 

 4. A similar extract of turmeric root. 5. An alcoholic extract of 

 litmus (dispersed yellow light). 6. A solution of chlorophyll in 

 alcohol. The result of these experiments was, that the first five 

 fluids were fluorescent, but no fluorescence could be detected in the 

 sixth. A repetition of this experiment gave the same results. From 

 this it would appear that the electrical light is deficient in the rays 

 which produce red in the solution of chlorophyll. 



I now instituted a series of experiments in order to ascertain the 

 eflPects of the light of a platinum wire ignited by the passage of an 

 electrical current. For this purpose a platinum wire of an inch and a 

 half long was fixed in such a manner, that porcelain saucers con- 

 taining the above-mentioned fluids might be placed beneath it. The 

 wire was then brought to a red heat by the current, and the fluids 

 placed under it one after another. These experiments were made 

 in a camera-obscura lined with black, and the result was entirely 

 negative. They were then repeated by pouring portions of the fluids 

 into test-tubes, holding them to the ignited wire, and looking in 

 from the top. Under these circumstances also no fluorescence could 

 be detected. Only the fluid No. 5 glittered with a reddish light, 

 but this is its ordinary colour. The experiment showed that the 

 light of the ignited wire contained many red rays. This fact agrees 



