370 Professor Sir James Dewar [Jan. 18, 



card fixed one on each side of the central black stand. These side 

 screens alone are snfficient for this purpose if the whole apparatus 

 stands in a good light. A striking contrast is obtained when the 

 column is drained to blackness and illuminated hj a beam from 

 below, if an occasional drop of soap solution is allowed to trickle 

 down through the nozzle. Before this is done very little is seen 

 except the bright point reflections from the curved surfaces ; but, as 

 the falling drops arrive in rapid succession at the planes between the 

 adjacent segments, the thin circular channels flash up into sparkling 

 silvery light from the internal reflections of the accumulated liquid. 

 Fig. 7 gives some idea of the appearance. 



The following particulars show how some of the results were 

 obtained : — 



(a) Nozzle, 3 cm. diameter; constriction, 1-15 mm. bore ; drop, 

 18 mgms. ; air current approximately 500 c.c. a minute ; drop 

 interval, 5 seconds ; giving a volume of 42 c.c. for each segment. 

 While they were being blown the free end was caught on one of the 

 movable glass rings already mentioned, by means of which fifteen 

 bubbles were steadily drawn out into a flexible catenary with its ends 

 13 cm. apart (Fig. 8). 



(h) Nozzle, 3*4 cm. diameter ; air current, 565 c.c. per minute ; 

 drop interval, 7h seconds ; giving a volume of about 70 c.c. for each 

 segment. A column of eight of these bubbles reached from the rim 

 of the nozzle to the wet floor of the cube, where contact was made. 

 The same nozzle could give a chain of nine bubbles of three times 

 this volume. 



(c) Same nozzle ; air current, 305 c.c. per minute ; drop interval, 

 9 1 seconds ; giving a volume of about 48 c.c. for each segment. A 

 column of ten of these bubbles was held on a fairly straight axis 

 inclined at about 50° to the horizontal after they were drained free 

 of excess liquid. 



Some of these chains are liable to break with excess liquid 

 (Fig. 8). This can be largely obviated by using a percentage of 

 hydrogen in the air current, provided an atmosphere of pure air is 

 maintained in the glass cube. The buoyancy of the bubbles is 

 thereby increased for a time sufficient to allow the column to be 

 manipulated. When the chain has once been secured any further 

 accumulation of liquid must be continually removed. For this 

 purpose a fluted glass rod some 2 mm. thick and 3 or 4 cm. long 

 was very effective. (It was made by drawing out a bundle of seven 

 small glass rods in the blow-pipe, and was utilised by attachment to 

 one of the movable bent glass rods passing through the top of the 

 cubical box.) 



When very large bub])lc segments are required it is safer to 

 interrupt the air current l)etween two adjacent segments, while a 

 few extra drops of liquid are run in to remoisten the glass surfaces. 

 In this way bubbles of over 1 litre were obtained on a nozzle 5 cm. 



