26 



KNOWLEDGE. 



January, 1913. 



system cools down, so the chloroform again sinks to the 

 bottom. This experiment is similar to those devised by Mr. 

 C. R. Darling : as, for example, with aniline and water. 

 The solubility of the liquids in each other causes the 

 equilibrium to become unstable and the position of the 

 liquids to reverse, at a temperature slightly different from 

 the temperature corresponding to equal density. Chloroform 

 and water have different indices of refraction, but as the 

 temperature rises the index of chloroform decreases more 

 rapidly than that of water, and when the two indices become 

 equal the separating surface disappears from view and gives 

 the appearance of complete homogeneity. 



THE PHOTOELECTRIC EFFECT.— When metal 

 surfaces are exposed to ultra-violet radiations, negative 

 electrons are expelled from these surfaces. •■ Each metal has 

 a definite photoelectric effect of its own. It is interesting to 

 gain knowledge of the emission velocities of the electrons from 

 the salts of metals and various compounds, and the work of 

 Dr. A. LI. Hughes supplies that information. It was necess- 

 ary to experiment with surfaces of which the state of the 

 surface is similar to the mass of the substance, because the 

 photoelectrons come from a layer only a few molecules in 

 thickness. This has been ingeniously effected by vaporising 

 the substance in vacuo from a small quartz bulb furnace, 

 electrically heated, on to a nickel disc lowered near the mouth 

 of the furnace. Most halogen salts show marked photoelectric 

 effect after exposure to light, but such substances as zinc 

 chloride or phosphorus pentoxide show no such effect. It 

 appears that only those substances which are decomposed by 

 light show the photoelectric effect, and that the light first 

 decomposes the surface and then acts on the metallic element 

 in the ordinary way. 



SILENT DISCHARGES.— In Chili, observations have 

 been made on the " Andes glow," which appears to start from 

 an altitude of ten thousand feet along a ridge or conical peak. 

 Luminous arcs up to 25° in width, surrounding a dark core, 

 or radial groups of rays shooting up as far as the zenith, were 

 observed, and lasted for several seconds. The phenomenon is 

 frequent on warm, clear nights. 



FLICKER. — When a disc with black and white sectors is 

 spun round at a moderate speed, a flicker may be seen ; on 

 increasing the speed the flicker disappears, but if the illumina- 

 tion increases the flicker may reappear if the speed is not too 

 great. The disappearance of the flicker is connected with the 

 speed, the intensity and hue of the illuminating light, and with 

 certain physiological effects on the eye. Dr. T. C. Porter has 

 investigated the connection between illumination and critical 

 speed at which flicker vanishes, and an abrupt alteration in the 

 relation occurs when a certain low illumination is reached, 

 and this must in some way be connected with the behaviour 

 of the eye. Mr. H. E. Ives has published a detailed investiga- 

 tion on the application of the " flicker " method to the photo- 

 metric comparison of lights of different hue, a problem of 

 considerable complexity. The relative brightness of differently 

 coloured lights is not constant under all conditions, owing to 

 two main physiological effects — the Purkinje effect and the 

 " yellow spot " effect. The former is the greater sensitiveness 

 of the eye to blue light at low illumination, and the latter is 

 the change of relative brightness of different colours when the 

 size of the field of view is changed and different areas of the 

 retina of the eye are illuminated. Mr. Ives has found the 

 reverse of these effects when experimenting with the flicker 

 method of comparing lights of different colours. There are 

 four methods open to the comparison of lights of different 

 hue, viz. : — 



(I) The estimation of the sensation of equal brightness. 



(II) The visual acuity or the estimation of the fineness 

 of detail detectable as the luminosity decreases. 



(III) The critical frequency or the comparison of the 

 intensity of the light illuminating discs of black and the 

 colour at the same speed of alternation. 



(IV) The " Flicker " method, when the two colours 

 alternate and the slightest change of either at a particular 

 speed produces " flicker." 



The work of Mr. Ives will certainly lead to a method of 

 comparing the intensity of light of different hue, but the 

 accuracy will always be dependent on the eye of the observer 

 to some extent. 



ZOOLOGY. 



By Professor J. Arthur Thomson, M.A. 



HOW DOES EXPERIENCE COUNT FOR THE RACE? 

 It is certain that many animals have an inborn capacity of 

 reacting in a definite and adaptive way to particular stimuli. 

 We call their behaviour instinctive. In many cases it seems 

 possible to think quite clearly about the possible origin of 

 these inborn capacities. We can think of them beginning as 

 germinal variations; we can think of them progressing as 

 germinal variations ; we can think of them being most subtly 

 perfected in the course of Natural Selection. And all without 

 supposing that the tutelage of experience counted for anything 

 except in the individual lifetime. This is the ordinary 

 Darwinian view, in contrast, for instance, to the view of 

 Professor Richard Semon, who holds very strongly that we 

 must suppose that the offspring directly benefit by the 

 premiums which their parents and ancestors have paid to 

 experience. And some of the cases of very specific instinctive 

 reaction are so striking that one is inclined, at first sight at 

 least, to conclude that the lessons of experience must be in 

 some way entailed. Let us cite one case taken by Semon 

 from Lenz's " Schlangen und Schlangenfeinde " (Gotha, 1870). 

 Lenztook two young buzzards from the nest and reared them. 

 They killed slow-worms and ringed snakes carelessly, but they 

 were in a most striking way excited when they first had to 

 deal with an adder. They had previously devoured pieces of 

 adder's flesh quite greedily, so it could not be smell that 

 pulled the trigger. Moreover, buzzards work by sight. Now, 

 what was it made the buzzards treat the adder in a way 

 entirely different from that in which they dealt with grass 

 snakes ? 



VINDICATION OF THE CABBAGE FLEA.— When we 

 turn up the well-known leaflets of the Board of Agriculture 

 under the heading Cabbage Flea or Haltica oleracea, we 

 find it stated that this little bluish-green beetle is often far 

 more harmful than the Turnip Flea, that " in some districts it 

 is the chief root crop and general pest," and that it " attacks 

 old and young plants, especially cabbages, but also turnip and 

 other crops." Now we do not wish to take up the cudgels on 

 behalf of flea-beetles, but it is of interest to call attention to a 

 vigorous protest by Franz Heikertinger in Vienna, who has 

 been engaged for seven years in a study of the Palaearctic 

 Halticinae. The cabbage flea has been grossly libelled. It 

 frequents Polygonaceae like buckwheat and Onagraceae like 

 willow herb. It does not frequent Crucifers, nor eat them, 

 nor develop on them. The fact seems to be that Haltica 

 oleracea has been carelessly mixed up with species of 

 Phyllotreta such as Ph. nemorum, the turnip-flea-beetle, 

 and with species of Psylliodes, such as Ps. chrysocephala. 

 It is strange that the mistake should have remained so 

 long undetected, and it is satisfactory to have it corrected. 

 For not only should justice be done even to a flea-beetle, but 

 it is of practical importance in agriculture, that the true culprit 

 should be persecuted. 



CTENOPHORES. — In his finely-illustrated memoir on the 

 Ctenophores of the Atlantic coasts of North America, Mr. 

 A. G. Mayer calls attention to the fascinating beauty of these 

 animals. " In the extreme tenuity of their bodily substance 

 and their diaphanous delicacy of coloration, the ctenophores 

 stand apart from other marine animals. Their presence in 

 the water is commonly denoted only by the brilliant flash of 

 rainbow colours, which play along the lines of their ciliary 

 combs as they move languidly beneath the unrippled surface 

 of the sea. Yet these creatures are no more wonderful in 

 their complex organization than in their remarkable adjustment 

 to their habitat; for so delicate are most of them that a 

 current such as that of an oar suffices to tear them into mis- 

 shapen shreds — a fate which they escape in time of storm by 



