274 



to the direction of the current. On making the circuit of the magnet, 

 and breaking it immediately, the luminous strata rushed from the 

 positive arid then retreated, cloud following cloud with a deliberate 

 motion, and appearing as if swallowed by the positive electrode. 



The amount of electricity which passed appeared materially in- 

 creased on exciting the magnet ; once the discharge was so intense 

 as to fuse half an inch of the positive terminal. 



After this had occurred, the discharge no longer passed as before 

 when the terminals of the battery were connected with it ; but on 

 connecting the positive end of the battery with the gas-pipes of the 

 building, the discharge passed. 



The discharge could also be extinguished by the magnet ; and 

 the time necessary to accomplish this, furnished a beautiful indication 

 of the gradual rise and reduction in the power of the electro- 

 magnet. 



III. " On Vacua as indicated by the Mercurial Siphon-Gauge 

 and the Electrical Discharge." By J. P. GASSIOT, Esq., 

 F.R.S. Received January 19, 1860. 



That the varied condition of the stratified electrical discharge is due 

 to the relative but always imperfect condition of the vacuum through 

 which it is passed, is exemplified by the changes which take place 

 in the form of the striae while the potash is heated in a carbonic 

 acid vacuum-tube. In order, if possible, to measure the pressure 

 of the vapour, I had a carefully prepared siphon mercurial gauge 

 sealed into a tube fifteen inches long, at an equal distance between 

 the two wires A, B. 



This tube was charged with carbonic acid in the manner described 



