1879.] Spontaneous Segmentation of a Liquid Annulus. 55 



top was "4 centim., and of the outer "625 centim. ; the principal 

 diameters being 5"35 centims. and 7*475 centims. respectively. B is a 

 sort of catapult to project the disk vertically downwards, and consists 

 of a short brass tube 3 centims. long, clamped vertically, in which an 

 inner tube c slides loosely, but is kept thrust out as far as the slots in 

 the outer tube permit, by the action of a strong spiral spring inside. 



By looping a string, s, over a small central hook in the disk, the latter 

 can be drawn up tight against the end of the outer tube, and 

 held firmly in a horizontal position, and then, after a known weight 

 of mercury has been poured into either groove, the end of the 

 string is let go, and the disk is shot downwards, leaving the mer- 

 cury annulus in the air. A tray of fine wet sand is placed below 

 the annulus to catch and preserve the impressions of the circle of 

 drops formed, while the disk is steered out of the way by striking 

 with its two projecting arms against the slanting brass rods, as shown 

 in the figure. 



The inclination of these rods should be such as to get the disk out 

 of the way as soon as possible, and will depend on the strength of 

 the spring used ; the stronger the better. 



The object of slanting the sides of the grooves is to prevent the 

 annulus being carried downwards by any friction with the disk. 



I have tried smoked glass, lard, and wet sand, for receiving the 

 drops and their impressions — the last is cleanest and answers best ; 

 the best consistence is easily found by practice, and depends a little 

 on the depth of fall. If too soft, the impressions of separate drops 



