June 24, 1921] 



SCIENCE 



567 



beams, so that the magnetic field would be in 

 the main horizontal and transverse to the light 

 of the sun entering downward as before. An 

 iron arc was arranged to be operated so that 

 the smoke from it would rise from below and 

 enter the field of the loop, and by changing 

 the relative position of the arc, the smoke col- 

 umn, widening as it rose, could be made to 

 bathe the turns of the coil, cross its axis, or 

 at a distance away, merely enter the field. As 

 the experiments thus far had always involved 

 connection to the shop plant, with 60 cycle A. 

 C. current, a cheek apparatus was set up, con- 

 sisting of a storage battery (of a type such as 

 is used in automobile starting) arranged on 

 a stand. In circuit with it, and under control 

 of a switch was a coil of about .2 meter d' 

 ameter and giving a field due to about 2,500 

 ampere turns when the switch was closed. 

 This second apparatus could be moved about 

 and was entirely independent of supply cir- 

 cuits, or static dusturbances which might be 

 present in them. 



The first tests were made with the trans- 

 former loop (representing a field of 20,000 

 ampere turns) and were very striking. The 

 rising smoke from the small iron arc, only 

 moderately visible in the sunbeam, became 

 decidedly luminous when the field was put on. 

 Each closure of the current switch to the 

 primary of the transformer was instantly fol- 

 lowed by the brilliant smoke effect, and the 

 effect instantly disappeared on the opening. A 

 black background had been provided in front 

 of which the smoke rose. After the arc had 

 been running a few minutes only, it was seen 

 that the air of the room was carrying suffi- 

 cient of the smoke particles to give the effect 

 anywhere in the space covered by the magnetic 

 field and the sunbeams, even a number of feet 

 away from the coil. In this case the appear- 

 ance was as if in the air there were diffused 

 some substance or material which only became 

 visible in the combined sunlight and mag- 

 netic field. That in this case the luminous 

 effect is not greater near the coil loop than 

 feet away, indicates that orientation, or what- 

 ever causes the effect, is complete even in a 

 rather weak field. Thorough ventilation of 



the room by opening windows, caused the ef- 

 fect to fade out gradually by removal of 

 the active particles. 



The experiments with the D.C. current coil 

 and battery conclusively showed that the 

 effect was present with it, as with alternating 

 current, and incidentally established the fact 

 that the effect on the particles is independent 

 of the direction of magnetization. It is 

 doubtful if high frquency tests would allow 

 us to discover whether the establishment of 

 the effect requires tima Probably not. 

 Observations made through the axis of the 

 loop of two turns show a minimum of effect, 

 from which it may be inferred that it is not 

 present if the viewing is exactly along the 

 field line direction. 



Polarization. — Having obtained, as de- 

 scribed in the foregoing, a controllable and 

 relatively brilliant source of the luminosity, 

 tests with the Nicol's prism were resumed. It 

 was soon noted that the polarization was de- 

 cided as controlled by the magnetic field. 

 Moreover, the very curious fact was discov- 

 ered by me that the fumes from the iron arc 

 were composite so far as analysis by the polar- 

 izing prism was concerned. The bluish colored 

 smoke arising gave but little effect, but there 

 was with it a yellowish gray fume, which was 

 highly luminous in one position of viewing 

 by the prism and invisible when the prism 

 was at right angles to that position. This in- 

 dicates complete polarization when the field is 

 on, for the light diffused from the particles in 

 the yellowish gray fumes. This is an extra- 

 ordinary effect, for which no evident explana- 

 tion suggests itself, for the field lines are not 

 straight but wrap themselves around the coil 

 or loop in curved directions, and the effect is 

 apparently complete even with the fumes risinr 

 in the space where the lines are strongly curved. 



It remains to use a vertical beam of light 

 and make tests from opposite directions across 

 the field, also to use artificial light instead of 

 sunlight. The design of a small demonstration 

 apparatus seems possible, consisting of a coil 

 to be put on a battery or lighting circuit, A.C. 

 or D.C, a small iron arc between two wires, a 

 box with darkened interior to be filled with 



