3tt6 Trowbridge — Electric Discharges through Hydrogen. 



beam by electrostatic action ; it readily passes when the current 

 is reversed. The phenomenon of rectification is shown in a prac- 

 tical way in the U-shaped tube represented in fig. 7, which 

 is provided with two anodes, A and A, and two cathodes, I) 

 and D'. The cathodes have orifices at their centers. The two 

 anodes are connected together, and also the two cathodes— the 

 tube forming a multiple circuit. A transverse magnetic field 

 can be so placed near one cathode that no current will pass in 

 the branch of the tube of which it is a part, while the current 

 passes freely in the other branch of the U tube. This form of 

 tubes rectifies an alternating current. 



The apparent repelling, or driving back action, of the cathode 

 beam on striae is shown in a suggestive manner in a straight 

 cylindrical tube when a diaphragm is inserted between the anode 

 and the cathode. We will take for illustration one branch of 

 the U-shaped tube (fig. 7), and suppose that the current is 

 led into the tube at A and out at D. A metallic diaphragm 

 with a small hole at its center is inserted in the tube about one- 

 third of the distance between A and D, measured from the 

 cathode to anode, the latter also having an orifice at its center. 

 The striae are slowly driven back by the cathode rays as the 

 exhaustion proceeds. At a definite stage of this exhaustion a 

 stria takes refuge behind the diaphragm near the anode, where 

 it is protected from the driving back action of the cathode 

 rays ; finally at higher exhaustions this stria is driven through 

 the orifice in the anode and shelters itself behind the anode. 



At a higher state of rarefaction a stria issues from the orifice 

 in the anode and this also shelters itself behind the diaphragm 

 on the side toward the anode. There are, thus, three definite 

 stages of stratification in this form of tube. At a pressure of 

 four centimeters fine striae appear on the side of the orifice in 

 the diaphragm opposite to the anode. These soon disappear 

 with increasing rarefaction. At a pressure of approximately 

 3 mm a large stria shelters itself behind the diaphragm opposite 

 the anode. This disappears with diminishing pressure ; and 

 at a pressure of approximately 15 mm a large stria w T ells up out 

 of the orifice in the anode and takes a similar place near the 

 diaphragm. When the state of canalstrahlen is reached, all 

 striae have been driven into the anode. Can we regard these 

 strahlen as a stratification which cannot be driven back by the 

 cathode rays ? In this form of tube we find evidence of suc- 

 cessive states of stratification which may depend upon positive 

 rays of different velocity. 



When we turn our observation of stratification in the neigh- 

 borhood of the cathode instead of in the neighborhood of the 

 anode, we find that a stratification always takes place on the 

 glass wall close to the entrance of the cathode, or to its sealing 

 in place. It can be produced equally well by causing the 



