242 



KNO\VLi:i)GK, 



JfNE. 1912. 



this cclobratcul test object. The iris iliaphr.iKin of the 

 condenser was closed siitTicieiitlv to ol)t:iin more general 

 sharpness. The orJKin.il |)lii)loj;raph. which is taken on an 

 .S.J X (1^ plate, is magnified cij^hlv di.inicteis. The camera 

 extension was one hinidred .ind sixty-three centimetres. A 

 jjreen screen was employed for contrast, and an exposure of 

 twenty seconds Riven on .in Imperial N.I', plate of speed 

 two hnndred and twenty-five H. and D. The negative was 

 developed with Pyro-soda developer. The two examples 

 accompanyini,' this article are from negatives taken at the first 

 of the series of practical demonstrations on photomicrography 

 given at the South-Western Polytechnic on Monday, May 6th, 

 and must not be regarded as the best that could be obtained, 

 when more time could be spent in the adjustment of apparatus 

 than is possible when demonstrating before a class. They are. 

 liowever, good, and serve their purpose perfectly, in illustrating 

 as they do the application of photography in low power photo- 

 micrography. 



I'lnsics. 



Hy Alfred C. G, Egerton, B,Sc. 



.\CTIVi: NITROGEN,— In the Proceedings of the Royal 

 Society are to be found further accounts of Profes.sor Strutt's 

 experiments on "active" nitrogen. It appears that "active" 

 nitrogen is nitrogen in the atomic condition, and not 

 polymerised as oxygen is in ozone (On). Oxygen destroys the 

 nitrogen glow; which glow appears to be the luminosity 

 afforded by the process of passing from active to ordinary 

 nitrogen, or in other words, to combination of nitrogen atoms. 

 The oxygen does not appear to actually combine with the 

 nitrogen, but acts as a catalyst and hurries the production of 

 ordinary nitrogen. One very important result is that active 

 nitrogen appears to play no part in the production of oxides 

 of nitrogen by the spark discharge. Hydrogen only dilutes 

 the nitrogen and does not take part in the action (N-f-N = N..). 

 Nitric oxide combines with active nitrogen, giving a greenish- 

 yellow^ Hanie, due to the nitrogen peroxide produced, in all 

 probability. Fourteen parts by weight of " active " 

 nitrogen give seventy-six parts of nitrogen trioxide and 

 consequently the amount of active nitrogen is about 2-5 per 

 cent, of the total nitrogen present. The active nitrogen has 

 the property of developing the metallic spectra when certain 

 volatile metals are heated in it ; ozone is known to do this 

 also in some cases, but all attempts to isolate active nitrogen 

 by condensation in liquid air have not succeeded. The 

 spectrum is simpler than the ordinary nitrogen spectrum ; and 

 considerations such as these point to the probability of active 

 nitrogen, being nitrogen in the atomic condition. 



The writer has noticed that the flame of ammonia burning 

 in oxygen has several peculiarities, which lead to the idea that 

 the first action — the action going on in the inner cone giving 

 a yellow luminosity — is merely the splitting up of the 

 ammonia into hydrogen and nitrogen atoms, which then 

 combine as in the case of active " nitrogen." The flame 

 has a colour and spectrum similar to that of the active 

 nitrogen glow ; the shape of the inner cone is always such that 

 it exhibits a rounded appearance indicating that it is a decom- 

 position rather than a combustion with upward rising gases 

 which produces pointed flames. There is a considerable 

 amount of nitrogen peroxide produced, but this would pro- 

 bably be due to the combustion of the molecular nitrogen 

 and o.xygen ; but the main products of combustion are 

 nitrogen and water. A sn:all yellow streak of the same 

 colour is noticeable in the flame of burning cyanogen between 

 the pink and violet cones, and may be due again to some 

 re-combining atoms of nitrogen. In these cases it is necessary 

 to distinguish the yellow flame due to the production of oxides 

 of nitrogen and the glow due to recomposition of nitrogen 

 atoms. 



SPECTRA. — Much work has been done recently on the 

 shift of the lines in the spectra of metals by the effect of 

 pressure. Pressure would at first sight only appear to change 

 the molecular conditions of a substance, and could hardlv 



affect the vibrations within incompressible atoms. However, 

 as Professor Richards and others have pointed out. it is a 

 fallacy to assume an incompressible atom, and it would seem 

 thai the change of wave-length of light emitted front atoms 

 unili'r high pressure is caused by a change in those properties 

 (if Ihi- atom which depend on the specific inductive capacity. 



Coblentz has recently examined the luminous eflficiency of 

 various gases contained in vacuum tubes, through which an 

 electric current is passed. The luminous efficiency of air, 

 carbon-dioxide, helium, and so on. is of the order fifteen to 

 twenty per cent., owing to a major proportion of the energy 

 being distributed as infra-red radiation. The infra-red 

 radiation in neon is almost entirely absent, and the luminous 

 efficiency is upwards of ninety per cent. 



Professor Jones has given an account of seme work on 

 absorption spectra and the solv.ile theory of solution in the 

 May number of The Philosophical Magazine. A salt 

 dissolved in a given solvent is characterized by a definite 

 absorption spectrum : when such is dissolved in varying 

 mixtures of two solvents only two definite absorption spectra 

 appear, one being characteristic of each solvent : only the 

 relative intensities of these two spectra change on changing 

 the relative proportions of the two solvents. Thus neodymium 

 chloride dissolves in alcohol and in water, giving rise to 

 methyl-alcohol bands and water bands, the intensity of which 

 depends on the amount of methyl-alcohol and water present; it 

 appears that there is evidence in favour of the view that there 

 are definite hydrates and alcoholates in solution. The solvate 

 theory of solution which is being developed by Jones and his 

 pupils supplements the theory of electrolytic dissociation, and 

 is not at variance with it. 



Havelock has found that the departures from Kundfs rule. 

 that the greater the refractive power of the solvent the greater 

 the shift of the absorption bands of a solute towards the red, 

 are due to the formation of molecular aggregates. It is well 

 known that Kundfs rule is only true for a few substances in 

 dilute solution. 



ZOOLOGY. 



By Professoi{ J. Arthur Tho.mson. M..^. 



SKIN OF HAIRLESS DOGS.— Darwin and others have 

 directed attention to the occurrence of hairless dogs, especially 

 in warm countries. They are often called by such names as 

 "Egyptian" and "Chinese." and many of them show- very 

 abnormal development of the teeth. .-V study of the skin of 

 such dogs has recently been made by F. G. Kohn. who finds 

 in the new-born puppy (II a variety of stages in hair-develop- 

 ment in a state of arrest, and (2) an abnormal development of 

 horny material and an abnormal distribution of pigment. On 

 the one hand, the skin is like that of a young embryo : on the 

 other hand it is abnormal. The condition is not a gradual 

 adaptive diminution of hair, such as may have occurred in the 

 case of man. It is an abrupt hereditary " umtation " of 

 unknown origin. 



FEATHERS AND SCALES.— Aristotle discerned the 

 deep-seated sameness of feathers and scales, and the view- 

 that they are homologous has been generally accepted. But 

 it is not without its difficulties, for the development of the 

 feather, though much nearer that of a scale than that of a 

 hair, is very distinctive. And there are no transitional types 

 between scale and feather. The minute flat feathers on a 

 penguin's wings are no nearer scales than are the plumes of 

 an ostrich. Soine light has been recently thrown on the 

 (piestion by Frieda Bornstein's careful study of the foot of 

 the capercaillie where feathers and scales occur in such close 

 association. The conclusion reached is this, that a feather 

 corresponds not to an entire scale, but to part of a scale, 

 another part being suppressed. The same view has been 

 previously maintained by Ghigi. 



ALLEGED RL'DIMENTS OF TEETH IN MODERN 

 BIRDS. — The fact that teeth occurred in the oldest known 

 fossil bird iArchaeopteryx), and in many of its extinct 

 successors as well, has led to a repeated search for hints of 



