136 ANNUAL OF SCIENTIFIC DISCOVERY. 



need not here be noticed. Before going further, let us remark, that 

 there is something wonderful in the experiments which have led nat- 

 ural philosophers legitimately to talk of the different sides of a ray of 

 light. The word " wonderful" which I have just used, will certainly 

 appear natural to those who are aware that millions and millions of 

 these rays can simultaneously pass through the eye of a needle, with- 

 out interfering one with the other. Polarized light has enabled 

 astronomers to augment the means of investigation by the aid of some 

 curious instruments, from which great benefit has accrued already, 

 among others, the polarizing telescope, or polariscope, merits attention. 

 In looking directly at the sun with one of these, telescopes, two white 

 images of the same intensity, and the same shade will be seen. Let 

 us suppose the reflected image of this orb to be seen in water, or a 

 glass mirror. In the act of reflection the rays become polarized, the 

 lens no longer presenting two white and similar images ; on the con- 

 trary they are tinged Avith brilliant colors, their shape having experi- 

 enced no alteration. If the one be red, the other will be green ; if 

 the former be yellow, the latter will present a violet shade, and so on ; 

 the two colors being always what are called complementary, or sus- 

 ceptible, by their mixture, of forming white. By whatever means 

 this polarized light has been produced, the colors will display them- 

 selves in the two images of the polarizing telescope, as when the rays 

 have been reflected by water or glass. The polarizing telescope, thus 

 furnishes a very simple means of distinguishing natural from polarized 

 light. 



It has been long believed, that light emanating from incandescent 

 bodies, reaches the eye in the state of natural light, when it has not 

 been partially reflected, or strongly refracted, in its passage. The 

 exactitude of this proposition failed, however, in certain points. A 

 member of the Academy has discovered that light emanating under a 

 sufficiently small angle, from the surface of a solid or liquid incandes- 

 cent body, even when unpolished, presents evident marks of polariza- 

 tion ; so that in passing through the polarizing telescope it is decom- 

 posed into two colored pencils. The light emanating from an 

 inflamed gaseous substance, such as is used in street illumination, on 

 the contrary, is always in its natural state, whatever may have been its 

 angle of emission. The means used to decide whether the substance 

 which renders the sun visible is solid, liquid or gaseous, will be noth- 

 ing more than a very simple application of the foregoing observations, 

 in spite of the difficulties which appeared to arise from the immense 

 distance of the orb. 



The rays which indicate the margin of the disc, have evidently 

 issued from the incandescent surface under a A r ery small angle. The 

 question here occurs, The margins of the two images, which the 

 polarizing telescope furnishes, do they, when viewed directly, appear 

 colored? then the light of these margins proceeds from a liquid 

 body ; for any supposition which would make the exterior of the sun a 

 solid body is definitely removed by the observations of the rapid changing 

 of the form of the spots. Have the margins maintained their natural 



