July 29, 1921] 



SCIENCE 



85 



large relatively to the particles in the stria- 

 tion covering the most of the surface of the 

 slide. But each of these straight settings of 

 globules possessed a singular appendage, gen- 

 erally at one end only, but sometimes at both 

 ends. It consisted of a brush-like tail com- 

 posed of the brown filamentous chains of par- 

 ticles like those covering the slide as noted 

 above. They gave the appearance of tufts, 

 suggesting a growth of beaded fibers from the 

 end of the string of globules. By focusing, 

 these tufts or tails could be seen as projecting 

 outward (upward) in an inclined direction. 

 This means that the tufts did not lie on the 

 slide surface, but sprang outward from the 

 globule which carried it. The globule at the 

 other end of the short chain (generally the 

 largest in the line) was often to be seen as 

 having a convergence upon it of the usually 

 parallel striae of the other parts of the slide, 

 indicating clearly that the globules strung to- 

 gether were acting as small magnets with poles 

 at each end, towards and from which poles, 

 the convergence and divergence of the mag- 

 netic lines was indicated by the fine striae 

 of particles taking their direction. 



The polariscope showed that the striated 

 smoke layer caught on the slide has the same 

 property of scattering or diffusing light (as 

 plane polarized light) that the smoke oriented 

 in the air by a magnetic field has, but, of 

 course, the slide preserves the orientation and 

 needs, to produce the results, no magnetic 

 field after its formation or deposition. The 

 slide covered with the striated smoke film 

 is, in fact, a polarizer. 



Examination between crossed Nicol's prisms 

 (dark field) discloses the fact that the tufts 

 of fine fibers carried by the rows of globules, 

 show as luminous spots on the black field, 

 clearly indicating that the groups or tufts 

 have a polarizing effect if they are in proper 

 relation to the rays passing through. 



As was to be expected, any hollow vessel or 

 enclosure capable of retaining the smoke from 

 an iron arc can be used in demonstrating the 

 original luminous phenomenon. A glass flask 

 of from 1 to 2 liters is readily sensitized, as it 

 were, by holding its mouth over an arc for a 



short time, allowing smoke from the arc to 

 enter, and then corking the flask. It may 

 then be used to show the effects by allowing a 

 beam of light to traverse it while held in the 

 field of a current-carrying coil. While this 

 was being done, it was noticed by Dr. Holl- 

 nagel of the laboratory that when the coil 

 was traversed by an A.-C. current of twenty 

 cycles, the flask, when near the coil, gave the 

 usual effect of increased luminosity of the 

 smoke in its interior. When, however, the 

 flask was removed from the coil a distance 

 of several feet, the steady luminosity was re- 

 placed by a flicliering which kept pace, not 

 with the alternations of current in the coil, 

 but with the cycles only. The flickering was,, 

 as it appeared, at the cyclic rate. This flick- 

 ering was noted even at a distance of twelve 

 feet from the coil, although the coil was but 

 7 inches in diameter and about 2 inches in 

 axial direction. The flickering is a curious 

 effect, and it is diificult to explain, especially 

 the fact that it appears to keep time with the 

 cycles and not the alternations of current. It 

 points to some sort of magnetic retention or 

 polarization of the iron particles of the 

 smoke. They may even rotate or oscillate in 

 obedience to the field fluctuations, but there 

 is needed much more work of investigation as 

 to the cause of the peculiar Ijehavior. The 

 experiment clearly shows that a very moderate 

 field intensity suffices for lining up the par- 

 ticles in the air, and so producing the lu- 

 minous effect. 



Emphasis is again given to the fact of the 

 extremely small amount of iron particles sus- 

 pended in the air, capable of giving a decided 

 effect. Elihu Thomson 



Thomson Laboratobt, 

 Lynn, Mass., 

 June 17, 1921 



SCIENTIFIC EVENTS 



THOMAS HARRIOT 1 



The tercentenary of the death of Thomas 

 Harriot, the mathematician and astronomer, 

 occurred on July 2. Not only was he the most 

 celebrated English algebraist of his time, but 



' From Nature. 



