272 



HARDWICKE'S SCIENCE-GOSSIP. 



this subject to the Academy of Sciences, by M. Ch. 

 V. Zenger. He observed that Mont Blanc occa- 

 sionally displays a blue-greenish glow long after 

 sunset, and succeeded in obtaining a night picture of 

 the mountain by means of this glow, which is 

 highly actinic. This he did by projecting the images 

 given by photographic lenses, in a dark chamber, on 

 a glass plate coated with a layer of Balmain's phos- 

 phorus instead of collodion. After a short exposure 

 thus, he removed the glass plate in the dark, and 

 placed it in contact with a moderately sensitive dry 

 photographic plate. After an hour of contact in the 

 dark, a picture was found on the plate with all the 

 details as in an ordinary photographic negative. 



I am unable to find the original account of this, 

 and only write doubtfully from memory. Perhaps 

 some of the readers of Science-Gossip may possess 

 the record, and be able to supply particulars. 



TEETH OF FLIES. 

 By/VV. H. Harris. 



No. 11. MYD/E URBANI, Meig. 



THE creature possessing the dental organs shown 

 in the present illustration belongs to the large 

 sub-family of the Muscidse, known as the Antho- 



Fig. 171. — Teeth of Flies, Mydtc urbani. 



Something of this kind was done many years 

 ago by Robert Hunt, but without the luminous paint. 

 He placed newspapers in the dark in a drawer, 

 covered with plain paper, and after a considerable 

 time, found some sort of impression on the plain 

 paper. 



myiidae. These flies may be distinguished from the 

 more highly developed or typical muscidse by the 

 arrangement of the veins of the wings. The 

 first posterior wing-cell is always fully open ; the 

 fourth longitudinal vein runs direct to the margin 

 of the wing, without being bent upwards towards 



