ELECTRO-MAGNETIC INSTRUMENTS. 39 



tact between the wires in the tube, G, is broken, a spark 

 appears, and the gases are immediately exploded. 



Price, $25.00 



Dr. Bird's Inversor.(F\g. F5 - 461 - 



461.) An instrument to re- 

 verse quickly the current from 

 the galvanic battery. Its action 

 is very simple, complete, and 

 convenient. A B is an arc of 

 solid brass, formed of three separate pieces, either distinct 

 from each other, with a cavity between them ; or else two 

 pieces of ivory are inserted, that the surface at the top may 

 be quite even. The two outer pieces of brass forming this 

 arc are connected together by a wire underneath the stand, 

 but the centre pillar has no connexion, with the others. A, 

 and the centre piece, have binding screws attached ; c and 

 D are two bars of brass, fixed to each other, so that when 

 one is moved the other follows it, yet there is no metallic 

 communication between them. There are binding screws at 

 one end of each, while the other ends fit tightly upon the 

 nrc. The whole cross moves stiffly round the centre pin. 

 The battery connexion being made with E and F, the object 

 to be galvanized placed between the binding screws of the 

 arc and the bars or cross, as represented in the cut, the 

 positive pole being at E, the current would traverse from D 

 to B, thence underneath by the connecting wire to A, from 

 A through the object to the middle piece, and from this by 

 c to F. Slipping the cross aside so that c is moved to A 

 (other things as before), the current would pass along D to 

 the centre piece, thence through the object to A, and back 

 by c to F, or to the opposite end of the battery. 



Price, $5.00. 



The Water Regulator for modifying Galvanic Shocks. 

 (Fig. 462, next page.) The water regulator, contrived by 

 Mr. Lockey, is a useful piece of apparatus for the purpose 

 of modifying the physiological effects of the galvanic shock 

 obtained by the medium of the self-acting coil or other 

 source of power. The most powerful shock can by this 

 regulator be readily reduced to one in the mildest form. In 

 the medical administration of galvanic electricity, this was 

 formerly a point of some importance, as obviating the neces- 



