176 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



bodies. The diminution, however, is very different with the 

 different metals. In reference to the prime angles for trans- 

 parent laminae of gold, platinum, and silver, he states that 

 they show an increase with the increase of the thickness of 

 the metal, but a different decree of increase for different col- 

 ors. The value of this angle was not altered by magnetizing 

 or electrizing the metallic mirrors. The effect of pressure, 

 or of the relative distance among themselves of the particles 

 of silver upon the angle of incidence, was most strikingly ex- 

 hibited with silver collodion films. These were obtained by 

 the process used in photography, the collodion film adhering 

 firmly to a plate of glass. This film contains, uniformly dis- 

 tributed, finely divided particles of silver. It is opaque, 

 even when very thin. If by a slight compression the silver 

 particles are brought nearer each other, the prime angle of 

 incidence varies considerably more than in the case of a layer 

 of pure silver particles on glass. This dependence of the 

 optical properties of a quantity of more or less transparent 

 and non-transparent particles, on the relative distance of the 

 latter, seems to him hardly compatible with the assumption 

 that absorption and dispersion of light are determined solely 

 by a mutual vibration of the molecules of the body, induced 

 by the vibration of the molecules of the ether. Lond.,Edin., 

 and Dub. Phil. Mag., XL VII., 321. 



OX THE FLIGHT OF BIEDS. 



By ingenious and precise experiments on the locomotion 

 of quadrupeds, birds, and insects, Marey has, during the past 

 ten years, created a new province of experimental physiol- 

 ogy. During this year he has elucidated one of the most ab- 

 struse points in the mechanical theory of flight. He has dis- 

 covered the manner in which the air reacts on the win^s of 

 the flying bird, and sustains the bird during its flight. The 

 steps by which he reached this beautiful discovery are in- 

 teresting, and we will rapidly narrate them. He construct- 

 ed an artificial bird, the proportion of whose parts and whose 

 moving force he had founded on data obtained from exper- 

 iments on flying birds. But when he tried his artificial 

 bird, he was surprised to find that in order for it to rise on 

 the wing he would be obliged to make its wings move with 

 from three to four times the velocity they really had. But 



