



Description of an Automatic 



Let B = battery. 

 « m> m ' == electro-magnets. 



" a, a' = wheels having one tooth, and revolving in 

 the direction of the arrows. 



£ = screw supporting the arm, carrying two platinum 

 wires p and p' . 



d = platinum disk carried by the float b. 



The two wires p, p f , are respectively above and below 

 the centre of the disk d. 



W= wheel with 40 teeth in which is inserted the screw S. 



n = a small steel wire passing through the brass cup c, 

 to prevent the disk d from revolving. 



e = an ivory disk inserted in the tube, to prevent the float 

 b from rubbing against the sides of the tube. 



Now suppose the mercury should rise in the short leg of 

 the siphon, as represented in the figure. The float b will 

 be raised, and cause the platinum disk d to come in con- 

 tact with the point of the platinum wire p y closing the 

 circuit through the electro-magnet m ; the armature of 

 which being attracted, unlocks the clock-work, and allows 

 the wheel a to make a complete revolution. By this 

 means the wheel W is advanced one tooth, which raises 

 the screw S the w Vo of an inch, and consequently carries 

 the point p f that distance away from the disk d. 



As long as the mercury rises, the magnet m will be 

 operated, and the platinum point p will be constantly kept 

 the of an inch above the disk d. 



If, on the contrary, the mercury falls in the siphon, the 

 under side of the platinum disk d will be brought in con- 

 tact with the point of the wire p' 9 thereby closing the 

 circuit through the magnet m' ; the armature of which 

 allows the one tooth wheel a f to make a complete revolu- 

 tion, thereby causing the screw S to be depressed the 

 -ysV^ of an inch, carrying, of course, the platinum point p f 

 with it. 



It will now be readily seen how the platinum disk d, 



