208 Intelligence and Miscellaneous Articles. 



action on the coherer ; and hence the arrangement was used for 

 some quantitative determinations. 



The refractive indices of a series of solid and liquid substances 

 were determined. The following values were obtained for the wave- 

 length in question corresponding to a value of JNT = 37'500x 10 6 . 



Paraffine rc = l*524 n 2 = 2S2 



Ebonite 1-739 3-02 



Crown-glass 2*381 5-16 



Flint-glass 2-849 8-41 



Sulphur 1-802 3 24 



Benzole 1-767 3-13 



Glycerine 1*843 3-4 



Oil of turpentine 1*782 3- 17 



Vaseline 1*626 2-65 



Oil of almonds 1-734 3-01 



Absolute alcohol 2-568 6-60 



Distilled water 8-972 80-45 



— Wiener Berichte, Julv 1896. 



A LECTURE EXPERIMENT ON DIATHERMANCITY. 

 BY DR. SILVIO LUSSANO. 



A very simple and elegant method of showing to a large audience 

 the transparency or opacity of bodies for calorific radiations is the 

 following, which is based on the change of colour some substances 

 experience by variations of temperature. 



Double iodide of silver and mercury is prepared in a fine powder. 

 At the ordinary temperature it has a beautiful canary-yellow colour, 

 changing to a purple-red at the temperature of about 49°, and 

 resuming its original colour when cold. This double iodide is 

 prepared by mixing in molecular proportions the two substances 

 Hgl 2 and 2AgI, then adding to the mixture alcohol which partly 

 dissolves the mercuric iodide ; the magma is then well stirred 

 together in a mortar, alcohol being added from time to time. The 

 mixture, which at first is red, then changes to orange, and, after 

 some time, becomes of a canary-yellow colour ; the alcohol is 

 allowed to evaporate, the magma being stirred all the time. 



The double iodide thus prepared is spread on cardboard, forming 

 a screen of a canary-yellow colour sensitive to calorific radiations. 

 If, then, this is placed below a metal ball strongly heated, the 

 colour of the screen changes, showing the heating due to the 

 radiations. The same thing takes place if a plate of ebonite is 

 interposed between the ball and the screen ; but if a plate of a 

 substance opaque to thermal radiations is placed on the ebonite, 

 the shadow of this plate is projected on the screen, showing a 

 yellow colour on a red ground. In this way it can be understood 

 that it is easy to obtain the projections of athermanous substances 

 enclosed between two ebonite plates. — Communicated by the Author 

 from 'II Nuovo Cimento/ May 1896. 



