802 Professor Sir James Dewar [Jan. 21, 



the effect being very much like tliat of some Japanese lacquer, 

 the simulation of a volcano enhancing this suggestion (see 3, 

 Fig. D). 



In an horizontal film many similar movements may be produced ; 

 the various stages observed in one case are figured at 4 to 7, Fig. 9, 

 the convection finally established passing in a coloured stream 

 across the black film, and back round either side through the 

 Gibb ring. 



Variation in. the amount of liquid near the Gibb ring has been 

 referred to as being a disadvantage for certain purposes. With the 

 object of avoiding this a ring support was arranged for the film. 

 Platinum wire about 0*2 mm. thick was used, and was sealed in 

 at the neck of the double bulb. The film was thrown as usual ; 

 the peripheral part between the wire ring and the glass was then 

 destroyed either by touching with a glowing pencil of carbon, or more 

 conveniently with a small sponge saturated with liquid air. "With such 



Fig. 10. 



an arrangement there is no actual necessity for an open way on both 

 sides of the film to equalise the pressure, because the film hangs free 

 of the glass. A simpler form of double bulb can then be used, with 

 the result that there is greater freedom in illuminating and viewing 

 the film. This was found to be especially desirable with the use of 

 ultra-violet light, for which purpose a quartz bulb was obtained of 

 the shape shown in Fig. 10. For some purposes the convex front 

 of the bulb may be replaced by a plane window set at a small angle 

 to the film in order to avoid subsidiary reflections. This form of 

 support is well adapted for showing the permanence of the film under 

 vibration, the wire ring being then sealed to the bulb neck at one 

 point only, and thus behaves as a sensitive index to anv vibration 

 communicated to the l)ulb. A spot of light reflected from the film 

 shows the movement. It can be seen that the film is not destroyed 

 even though strongly vibrating when the ring is projected in profile ; 



