568 



SCIENCE 



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



fumes, having two sides of glass, one for the 

 admission of the light beam and the other a 

 window at right angles for observation. Two 

 coils placed outside the bos space and oppo- 

 site each other, or capable of application in 

 different relations will have advantages. The 

 addition of eye shields to cut out extraneous 

 light and a tortuous chimney conveying the 

 smoke but cutting off the light from the iron 

 arc are desirable additions to the equipment, as 

 also an analyzer as part of the apparatus for 

 the polarization effect. 



The Microscope. — Attempts have been made 

 to catch the particles in the smoke from the 

 arc upon a glass slide for microscopic exami- 

 nation as to their form under high powers. 

 That they are exceedingly fine is evident from 

 their remaining in suspension so long in the 

 air and diffusing themselves rapidly through- 

 out the air. That an exceedingly small amount 

 of material suffices for making the whole air 

 of a large room capable of showing the effect is 

 evident also. The sunbeam may enter the 

 room and its course is not disclosed by them 

 unless the magnetic field exists. It seems 

 natural to suppose that the particles consist of 

 some form of iron or iron oxide, but without 

 proof this can not be fully decided. Other 

 particles might exist giving such an effect, but 

 it must be confessed this does not seem prob- 

 able. Other fumes and smokes from arcs so 

 far have given no results. The smoke from a 

 nickel arc does not give the effect. Neither 

 does a cobalt arc yield fumes behaving like 

 iron smoke. 



The fumes and smoke of an iron arc were 

 caught on a clean microscope slide \intil a 

 patch of sediment of a slightly yellowish 

 brown tint, but very pale, was deposited. Un- 

 der moderate powers, very little of any defi- 

 niteness is shown, but under the high power 

 of an oil immersion lens of about 1.5 mm. 

 focal length, there is disclosed a curious struc- 

 ture of particles seemingly between .0002 and 

 .0001 mm. diameter, which particles are fre- 

 quently strung together, 4, 5, 6, or more, in 

 a line, giving the effect of a short piece of 

 chain made of small roundish particles, 

 slightly spaced apart, or of a short section 



of a string of beads (round beads) not touch- 

 ing one another. Many of these structures 

 appear to be straight, and some are curved. 

 Evidently in a magnetic field these chains of 

 particles, presumably of oxide of iron, and 

 magnetic, would line up and reflect or diffuse 

 light of the sun striking them. If the direc- 

 tion of vision was such as to favor polariza- 

 tion of the rays in a direction nearly at right 

 angles to the incidence of the solar beam, the 

 polariseope effect would be accounted for, 

 measurably. Aside from polarization, the 

 lining up of the chains would also account for 

 the extra visihility of the smoke under the 

 conditions of the experiment. 



It would seem from the foregoing that a 

 considerable length of column of smoke from 

 tlie iron arc, and subjected transversely to a 

 magnetic field, might be expected to act as a 

 means for obtaining polarized light in the 

 direction of the beam itself. This assumes 

 that there will be a considerable scattering 

 of light polarized as above described in a 

 direction sidewise, leaving the light which 

 passes through polarized in a plane at right 

 angles. The apparatus might be compared in 

 its action to a Nicol's prism, transmitting rays 

 in one plane and throwing out laterally those 

 in the other plane. This suggestion will be 

 tested as soon as proper arrangements can be 

 made. 



The polarized light which is sent out from 

 the smoke particles in a direction transverse 

 to the sunlight beams, when the magnetic field 

 is put on, is in the same plane as that re- 

 flected from a sheet of glass at the polarizing 

 angle receiving the same beam. This fact 

 is in accordance with what might be expected 

 if the short sections of chain or beaded par- 

 ticles were oriented or lined up by the mag- 

 netic field; the transverse waves of light vi- 

 brating in a plane intersecting the length of 

 the chains would not be deflected on account 

 of the extremely small diameter of the par- 

 ticles composing them, but waves vibrating in 

 the plane of the length of the chains would 

 be reflected to the side and this would account 

 for their plane of polarization being what it 

 is. Such waves would behave as if reflected 



