566 



SCIENCE 



[N. S. Vol. LIII. No. 1382 



the work and back was carrying about 7,000 

 amperes, and that the luminous effect was 

 spread in the space in which would be located 

 the magnetic field from this loop; that the 

 sunlight was entering the building through 

 high windows and shining across the space in 

 which the field was produced at intervals ; that 

 the effect was most conspicuous when one 

 looked towards the shadows, and across the 

 sunbeams, and also across the magnetic field. 



This would be expressed by saying that the 

 best effect was observed when the line of 

 vision was downward at an angle intersecting 

 the entering sunbeams, and into the shadows 

 under the beam furnished fortunately by a 

 partition a few feet high, over which the 

 sunlight came. The magnetic field, neglect- 

 ing the curvature of the lines, was, generally 

 speaking, at right angles to the line of sight 

 and to the direction of the sunlight. My son 

 also noticed that the effect of increased lumi- 

 nosity was coincident with the putting on of 

 the current and disappeared at once on cutting 

 off the field. It was thus clear that it de- 

 pended on the establishment of the magnetic 

 field. He reported these facts to me and they 

 were confirmed by me. Other observers were 

 soon enlisted, and on several favorable sunny 

 days all the above observations were confirmed 

 by them. Further, my son had not been able 

 to see any effect when looking across the sun- 

 beam from the opposite side. This means that 

 with the sunbeams streaming in from the 

 south, the effect was observed looking south- 

 ward and downward; the windows admitting 

 the light being to the south. Looking from 

 the south across the beam gave no result, 

 though it was not possible to look directly 

 across the beam on a slant upward into any 

 dark shadows and at the same time have the 

 line of vision cross the magnetic field. 



It is interesting to note at this point that 

 the luminosity filled the whole space and ex- 

 tended as far away as four feet or more from 

 the magnetic loop, and that it was not espe- 

 cially noted as more intense near the loop than 

 at a distance therefrom of say two feet or 

 more. 



Mx. Malcolm Thomson had further observed 



that by cutting out the loop from the secon- 

 dary terminals (clamps) of the welding trans- 

 former and simply joining those terminals 

 by an iron bar, as is done in resistance weld- 

 ing, the luminous effect in the neighborhood 

 of the transformer was still visible, but was 

 much more feeble than when the heavy loop 

 was used. It occurred to me to examine the 

 light by a large Nicol's prism. It was found 

 that there was a distinct polarization of the 

 light from the space. This means that when 

 the magnetic field was on, the sunlight was 

 scattered in the direction of the observer, from 

 the space occupied by the sunlight beam and 

 the magnetic field, and that such scattered or 

 deflected light was polarized. 



It occurred to me, as a possible factor in 

 the case, that as the building was used in part 

 to carry on arc welding by iron arcs, there 

 might be suspended in the air of the building 

 iron particles or finely divided oxides or com- 

 pounds of iron, which in some way were 

 oriented by the magnetic field, resulting in 

 the scattered light noted. This was con- 

 firmed in part by making the test observations 

 when the large doors of the building had been 

 open for some hours. The effect was present 

 though difficult to detect. This led to the 

 suggestion to bring an iron arc into operation 

 near the space in which the luminous effect 

 had been seen. This was done and with an 

 enhancement of the effect. 



At this stage, the further observations were 

 carried on in the Thomson Laboratory at 

 Lynn, Mass., with the aid of the laboratory 

 corps (A. L. EUis, H. L. Watson, Dr. Hohl- 

 nagel, and others). 



Two sets of test apparatus were prepared at 

 my suggestion. One large welding trans- 

 former was mounted in a special room, into 

 which the sunbeams could be received in the 

 afternoon, as the windows faced south by west. 

 The secondary terminals were joined by p 

 large loop of heavy copper cable about 12 

 square centimeters section and of a loop di- 

 ameter of .6 meter. The loop consisted of two 

 turns. The plane of the loop was vertical and 

 was nearly north and south, or in a plane 

 parallel to the direction of the entering sun- 



