Section III, 1917 [137] Trans. R.S.C. 



An Automatic Device for Ike Make and Break of Electric Currents 



By O. M A ASS 

 Presented by Dr. R. F. Ruttan, F. R.S.C. 



(Read May Meeting, 1917.) 



During the course of some experimental work, it was found 

 necessary to stir a viscous solution continuously by means of an 

 electromagnet. The stirrer employed had a definite period which was 

 made up of two unequal parts, the time of rise when the elctro- 

 magnet acted, and the time the stirrer fell due to its own weight. It 

 was, therefore, necessary to devise an apparatus by means of which the 

 electric current could be sent through the electromagnet for a definite 

 length of time and turned off for a definite length of time. The follow- 

 ing is a description of such an apparatus w'hich also has the advantage 

 of handling heavy currents at high voltages without requiring a relay. 



The apparatus is represented by the accompanying diagram 

 drawn to scale. It is made entirely of glass tubing, the shaded portion 

 being mercury, (a) Shows the mercury levels at the start. Tube A 

 leads to an ordinary water suction pump. When the suction is started 

 mercury rises in tubes B, C and D until, as shown in (b), the pressure 

 has been reduced by 30 cms. of mercury, the length of tube C being 

 30 cms. The mercury from F is then completely drawn into B allowing 

 free access of air to the suction pump through F. and C. The mercury 

 falls in D and rises in G to its former level. The mercury in B and E 

 seeks its own level which, on account of the addition of the mercury 

 from F and C, is higher than M, the tube connecting E and F. Some 

 mercury will therefore flow out of E into F closing tube C so that the 

 mercury in D, B and C is once more drawn up by suction. 



Thus the mercury in G automatically is made to rise and fall 

 through 30 cms., the number of cycles in a given time depending on 

 the amount of suction applied at A, which is easily controlled by 

 means of a tap. 



H is one terminal making permanent contact with the mercury 

 in G; K is the other terminal leading through a wire in a glass tube 

 (from the end of which it emerges) to the mercury in G. When the 

 mercury has fallen 20 cms., contact is broken and then the mercury 

 falls another 10 cms. (see (b)) before returning to its original level and 

 again making contact on the way. Thus during two-thirds of the time 



Sec. 3, Silt. 10 



