178 



SCIENCE. 



[N. S. Vol. XV. No. 370. 



in falling and have therefore sunk deep- 

 est before losing their liquid load. The 

 strata mount upward as fresh exhaustion 

 proceeds. The last colors to appear are the 

 browns and yellows of the first order, also 

 seen in the steam tube for vanishing con- 

 densations. The whole phenomenon is thus 

 the result of strata of invisible nuclei, 

 graded in virtue of the loading mechanism, 

 and partakes throughout of a mechanical 

 character to the extent that the nuclei are 

 not even a uniform product. The forced 

 distribution is sufficiently powerful to en- 

 tirely mask the elementary optical phe- 

 nomenon.* 



On shaking the liquid benzine in the 

 receiver uniform distribution is again pro- 

 moted, with the result that annular coronas 

 reappear. It is particularly to be noticed 

 that subsidence is due to loaded nuclei. 

 The free nucleus does not appreciably de- 

 scend. Even with water vapor, loading 

 does not produce stratification. AVater fogs 

 when exceptionally dense may sometimes 



* Since writing the above I have made similar 

 experiments with benzol, reaching the additional 

 result that nuclei are produced by the liquid it- 

 self, spontaneously, in the dark. They ascend 

 against gravity in horizontal strata, at the rate 

 of 2 or 3 cm. per sec. in the lower hemisphere. 

 They may be completely precipitated by partial 

 exhaustion, leaving the air in the vessel free from 

 nuclei (but the above flask will be refilled to sat- 

 uration in 10 or 20 minutes). The experiment 

 may be repeated any number of times. The sharp 

 demarcation of the pure air above from the rising 

 surface of nuclei is beautifully evidenced by the 

 coronas, which are annularly perfect for axial 

 beams below the surface, asymptotically bowl- 

 shaped at the surface, and absent for axial beams 

 above the surface. Shaking produces the coronas 

 from pure air instantly, but these are usually 

 smaller. In so far as the spontaneous coronas have 

 fixed diameters for fixed exhaustions (supersatur- 

 ation ) , the number of nuclei eventually reaches a 

 maximum or saturation. Among many interest- 

 ing problems growing out of the present observa- 

 tions, the corresponding behavior of water is 

 most important. 



be seen to rise, but the diffraction pat- 

 tern is always annular and usually with- 

 out color distortion. 



Carl Baeus. 

 Beown Univeesitt, 

 Peovidence, R. I. 



DATA ON SONG IN BIRDS: THE ACQUISI- 

 TION OF NEW SONGS. 



The purpose of this paper is to set forth 

 the evidence that has come under the 

 writer's personal observation regarding the 

 propensity of birds to acquire new methods 

 of expression in song. 



This faculty may be properly divided 

 into three categories: First, the disposi- 

 tion of wild birds to interpolate new phra- 

 sing into what may be called their normal 

 song, or to acquire new songs. Second, 

 education of expression, by direct teaching 

 from man to birds in confinement. Third, 

 the propensity of caged birds to imitate, 

 voluntarily, sounds that attract their 

 attention. 



The evidence under the first division of 

 this thesis is absolute and also well known. 

 However, a few special cases may serve to 

 emphasize the matter. 



Every trained field ornithologist dis- 

 criminates individuality in song, and some 

 have been so fortunate as to have noted 

 wide and radical departures from what I 

 have distinguished as the normal song. 

 The slight variation from the normal is of 

 too common occurrence to be dwelt on here. 

 Suffice to say that as set forth in a previous 

 paper in this journal,* most observers 

 recognize degrees of excellence in the songs 

 of vsdld birds of the same Idnd. 



Again, a few observers have heard wild 

 birds imitate or produce not only the songs 

 of other birds, but also the barking of dogs, 

 human speech and mechanically produced 

 sounds such as the crealdng of a wheel, the 

 filing of a saAV and the like. The facility 



•See Science, October 4, 1901, p. 522. 



