400 SCIENTIFIC KECOKD FOR 1885. 



" It is difficult for us living in dense air to conceive of the state of at- 

 tenuation probably present in the outer parts of the corona. Mr. Crookes 

 has shown by experiment that matter reduced to one-millionth part of 

 the density of ordinary air is still possessed of a sufficient number of 

 molecules to display a perfect corona when under the influence of an 

 electric current. In any case we may hope that our present knowledge 

 on the subject will be much increased by the daily photographs of the 

 corona, which are about to be commenced at the Cape by Mr. Ray 

 Woods under the direction of Dr. Gill." {Bull. Astron., June, 1^85.) 



Professor Yotmg on the solar corona. — In an article on '• Theories re- 

 garding the sun's corona," in the North American Review, Professor 

 Young expresses "his complete conviction that the corona is mainly 

 solar." He points out that the corona sends us three kinds of light, the 

 spectroscopic evidence showing that reflected or diffused sunlight is 

 present, though not the main constituent of the coronal luminosity, the 

 continuous spectrum indicating the presence of incandescent particles, 

 solid or liquid, whilst the bright lines show the presence of luminous 

 gases. These mingled gases form what has been called the " coronal 

 atmosphere," but in it " there are filaments and streamers and other 

 forms that are probably not gaseous, but composed of mist and dust ; 

 some of them may be of meteoric origin, and some composed of matter 

 ejected from the sun, while others perhaps are due to condensation of 

 vapors." The analogy of the channels in the tails of comets to the 

 coronal rifts, and the evidence comets afford to a repulsive force ex- 

 ercised by the sun, strike Professor Young as they do Dr. Huggins : 

 "All the luminous phenomena of the corona could be accounted for by 

 an atmosphere of a density millions of times below that in anj^ vacuum- 

 tube ever constructed." 



Photographing the corona in full sunshine. — Mr. W. H. Pickering, of 

 the Institute of Technology, Boston, made a series of attempts during 

 the partial eclipse of March 16, 1885, to obtain a photograph of the 

 corona. In this he was quite unsuccessful, for though his plates showed 

 several corona-like markings, they were clearly not due to the true 

 corona, as they were found in front of the moon as well as on the sun's 

 limb. From this Mr. Pickering was evidently led to conclude^that the 

 results which Dr. Huggins had obtained were probably of a similar 

 character, and he expressed as much in a letter to Science. Dr. Huggins 

 in reply pointed out that Mr. Pickering's method was faulty and was 

 calculated to produce such false images. The latter, therefore, some- 

 what modified his apparatus without, however, altering the two points 

 which Dr. Huggins considered most erroneous, viz, the use of an object- 

 glass instead of a reflector, and the placing his drop-slit close in front 

 of the object-glass instead of in its primary focus. The result has been 

 that he has obtained photographs free from false coronae, but showing 

 no real ones. At the same time he has made experiments which con- 

 vince him that to produce a perceptible image of a coronal rift it its 



