July 13, 1906.] 



SCIENCE. 



49 



mercury connected metallically to the earth; 

 and the wire on the inside of the tube was 

 connected to a quadrant electrometer. Under 

 these conditions, positive electricity was dis- 

 charged from the wire, for five or six minutes, 

 and the electrometer indicated the accumula- 

 tion of a negative charge. After the expira- 

 tion of ten minutes, the electrometer indicated 

 the accumulation of a positive charge, and the 

 emission from the wire of negative electricity. 

 This is in accord with the accepted views as 

 to the charges carried by the a and ^ rays. 

 Radium A radiates a rays only, and radium 

 C, both a and fi rays. Further, radium A 

 disappears in ten minutes, so that the a rays, 

 coming from radium A and radium C, passing 

 through the rubber, caused a negative charge 

 to appear on the wire for the first few minutes. 

 After ten minutes radium A disappeared, and 

 the positive charge appearing at that time was 

 due to the (S rays of radium C, the ft rays 

 passing through the rubber more easily than 

 the a rays. 



In the second series of experiments, a wire 

 was made radioactive as before, and placed 

 inside of and coaxial with a metal tube, the 

 diameter of which was very slightly greater 

 than that of the wire. The metal tube was 

 made air-tight, and the air within it rapidly 

 exhausted to a pressure of about one tenth of 

 a millimeter of mercury. The wire being 

 connected to the electrometer, and the tube to 

 earth, the deflections of the electrometer indi- 

 cated a continual accumulation of a positive 

 charge from the very start. A series of care- 

 ful measurements were made of the rate of 

 discharge of negative electricity from the wire 

 at different instants of time after the wire 

 had been taken out of the emanation. These 

 measurements showed plainly that the rate of 

 discharge of negative electricity was not pro- 

 portional to the ordinary ionization effect of 

 the induced activity; that is, was not propor- 

 tional to the quantity of radium A and C 

 present on the wire. The curves, represent- 

 ing the decay of the rate of emission of elec- 

 tricity, are much steeper than those represent- 

 ing the rate of decay of the ionization cur- 

 rents, except for the first ten minutes. They 



agree, approximately, with the theoretical 

 curves, given by Rutherford, representing the 

 sum of the quantities of radium B and radium 

 C on the wire. From this we may conclude 

 that radium B, which hitherto has been con- 

 sidered non-radioactive, emits, approximately, 

 as much negative electricity as does radium C. 



If the tube and wire are placed in a mag- 

 netic field, so that the lines of force of the 

 field are parallel to the axis of the tube, the 

 rate of emission of electricity is considerably 

 decreased. Further, an electromotive force 

 of a few volts will stop a portion of the dis- 

 charge of electricity. From these two experi- 

 ments, it appears, using the usual formulas, 

 that the ratio of the charge to the mass of the 

 carriers of this negative electricity is, at least 

 roughly, equal to that of the /? rays. The 

 experiments, however, give only the order of 

 magnitude of this ratio. The velocity, too, 

 of the carriers is very much smaller than that 

 of the y8 rays, which explains the fact that the 

 rays do not pass through the thin rubber tube, 

 and do not produce a sufficient ionizing effect, 

 to have been discovered by the ionization of 

 gases. The small velocity indicates that the 

 carriers are probably similar to those called 

 by J. J. Thomson 8 rays. 



A much more detailed account of the ex- 

 periments will be published as soon as the 

 absolute quantity of electricity emitted by a 

 given quantity of induced activity has been 

 measured. 



William Duane. 



the usb of astronomical telescopes in de- 

 termining the speeds of migrating birds. 



During the spring and fall of 1905 there 

 was developed at the University of Illinois 

 Observatory a method of determining the 

 heights of migrating birds. Two observers 

 watched the moon's disk at night through 

 small telescopes placed some distance apart, 

 and from the different paths seen projected 

 against the moon from the two stations, it 

 was possible to compute the height and direc- 

 tion of flight for each bird. These methods 

 and results are given in papers by Messrs. 



