LETTERS TO THE EDITOR expansion for only a of the discharges of the telescope. At the present time 1000 photos have been taken (equiva lent to 4000 if the cut-off counter had not been used Two tracks of interest, in that they have ionization densities definitely greater than usual, have been obtained one A(see Fig. 2)is believed due to a proton and the other B (see Fig. 3)to a particle of mass approximately 130 times the rest mass of an electron. Track A which terminated in the lead strip at the center of the chamber exhibited an ionization density 2, 4 times as great as the usual thin tracks and an Hp value approximately 2X10 gauss cm in a direction to indicate a positive particle Track B which passed out of the lighted region above the lead plate had an ionization density about six times as normal thin tracks (the to permit an accurate ion count) and an Hp value of that i gauss cm. If it is assumed, as seems reasonable, 96×104 above, the sign is negative. If it is taken that the ionization density varies inversely as the velocity squared, the rest mass of the particle in question is found to be approximately 130 times the rest mass of the electron. Because of uncertainty in the ion ount this determination has a proba FIG, 3, Track B 25 percent. In any case it does not seem possible to explain this track as due to a proton traveling up, for the observed Hp value would indicate a proton of 4.4x105 electron one cm in the chamber The track is clearly visible for The only possible objection to the conclusions reached above is that the bending of track A is largely due to istortion but this is ver unlikely, for the deflection is quite uniform and has a maximum value greater than ter times any distortions usually encountered in the thin tracks of high C, STREEt E. C. STeVeNSON 可吧能 Variation of Initial Permeability with Direction in Single on Magnetic measurements at flux densities ranging from single crystals of 3.85 perce iron, in the crystallographic direction [100], [110] and [111]. Up to this ti reported on the magnetic properties of single crystals at ch low flux densi hat single crysta Large crystals were produced in an atmosphere of pure IG.4. Photograph of the track, of a penetrating particle of high were cut in the form of hollow parallelograms. Each