March i, 1894] 



NATURE 



41 



contains a paper by Dr. G. H. Bailey, on some aspects of town 

 air as contrasted with that of the country. He proves that as 

 a means of discriminating between polluted and unpolluted 

 air, and as a means of forming some estimate of the extent of 

 pollution, the determination of the sulphurous compounds and 

 of organic matter are much to be preferred to that usually 

 adopted, viz. an estimation of the carbonic acid. It is also 

 urged that however minute the quantities of polluting matter 

 may be, they are sufficient to bring about serious disorganisation 

 in plant life and in human beings. Dr. Bailey has prepared a 

 number of tables showing considerable variations in the quantity 

 of sulphur compounds present in different localities in Man- 

 chester and London on clear days and on slightly or densely 

 foggy days. A remarkable result derived from one of the tables 

 is that during the dense fogs of December, 1892, in Manchester 

 and London, there was a much larger proportion of sulphur 

 compounds present in the London than in the Manchester air, 

 notwithstanding the fact that the coal consumed in Manchester 

 is generally understood to be much more sulphurous than that 

 burnt in London. 



An ingenious method of photographing the spectrum of 

 lightning is proposed in the current number of Wiedemann' s 

 Annalen by G. Meyer. The difficulty of directing the slit of 

 the spectroscope upon the flash is got over by substituting a 

 diffraction grating for the prism. A grating ruled on glass is { 

 placed in front of the object-glass of the apparatus, the object- 1 

 glass being focussed for infinite distances. Under these circum- 

 stances several images of the flash are obtained, a central image 

 produced by the undiffracted rays, and images of the first and 

 higher orders belonging to the diffraction spectra. The number 

 of images of each order corresponds to the number of lines in 

 the spectrum of the lightning. The arrangement was tested 

 during a night thunderstorm. Two plates were exposed in a 

 camera with a landscape lens of 10 cm. focal length, provided 

 with a grating with 40 lines to the mm. One of the plates 

 showed two flashes with their diffraction images of the first 

 order, but representing one line only. The other showed a 

 number of flashes, and one very strong one, passing apparently 

 between two chimney-pots, with its diffraction images well 

 marked. A calculation of the wave-length of the light produc- 

 ing these images gave 382 ju/x. The measurement was not 

 sufficiently accurate to warrant an identification of this line with 

 a known wave-length, but it is certain that a radiation of about 

 this wave-length must be added to the lines determined by 

 Schuster and Vogel. It is probable that with better apparatus 

 the method may be made to considerably increase our know- 

 ledge of the ultra-violet spectrum of lightning. 



The current number of the Electrician contains an abstract 

 of a paper, by J. Sahulka, on the measurement of the capacity of 

 condensers under alternating currents. The author has found 

 that condensers with a solid dielectric have a smaller capacity 

 when used with alternating currents than is given by measure- 

 ment by direct current methods. He considers that the reason 

 for this phenomenon lies in the condition of the dielectric; for 

 €ven if it has a very high electrical resistance it absorbs energy 

 in the process of charging, which energy is partly returned to 

 the circuit in the discharge, and partly converted into heat. 

 Thus, if a measurement of charge or discharge is made, the 

 galvanometer deflection is too high, for it is a measure not only 

 of the quantity of electricity passing on to or out of the coatings, 

 but also of that taken up or returned by the dielectric. Now it 

 is well known that the dielectric takes an appreciable time to 

 take up this quantity of electricity, and since in alternate-current 

 working charge and discharge occur successively -with great 

 rapidity, it follows that the dielectric has not time at every 

 charge to take up as much electrical [energy as it would if it 



NO. 1270, VOL. 49] 



were charged by an electromotive force applied for a much 

 longer time. It is thus necessary to define what is meant by 

 the capacity of a condenser where alternating currents are con- 

 cerned, and the author proposes the following definition : — ' ' The 

 capacity of a condenser on an alternating current circuit is equal to 

 the reciprocal of the product of 2 ttw and its inductive resistance, 

 the latter being equal to the quotient of the potential difference 

 at the condenser terminals caused by the charge, divided by the 

 strength of the current flowing into it." The author mentions an 

 experiment on a condenser with paraffined paper as dielectric, 

 having a capacity of about one microfarad when measured on 

 direct currents, which was found on an average of several experi- 

 ments with alternating currents to have a capacity about 14 per 

 cent, lower. Steinmetz's law, according to which condensers 

 having solid dielectrics should absorb, under alternating 

 Currents, an amount of energy proportional to the square of 

 the potential difference, was found by the author to be very 

 approximately true. 



We have received a copy of the seventh annual report of the 

 Liverpool Marine Biology Committee and their Biological 

 Station at Port Erin (Isle of Man), by Prof. W. A. Herdman, 

 P'.R.S. The report shows that progress has been made in the 

 scientific exploration of the Irish Sea during 1893, ^"d a number 

 of important investigations have been carried out by the sixty 

 natui^alists who worked at the station. The protective coloura- 

 tion of Vibrius varians was under observation during last 

 summer. The manner in which individuals of this small prawn 

 resemble the green, red, or brown seaweeds with which they are 

 associated, on even sandy and gravel bottoms, was discussed in 

 the report for 1S92, and the question was raised as to whether, 

 or to what extent, the adult animal could change its colour. 

 Prof. Herdman says that a number of specimens, of various 

 colours, were kept under observation in the laboratory during 

 the year, in jars with various colours of seaweed and of back- 

 ground, and in very different amounts of light. The results of 

 these experiments show clearly that the adult animal can change 

 its colouring very thoroughly, although not in a very short space 

 of time. The change in colour is due to changes in size and 

 arrangement of the pigment granules of the chromatophores. 

 It is remarked that an interesting point to determine is whether 

 in this case, as in some others of similar colour changes, the 

 modification of the chromatophores is due to nerve action and 

 is dependent upon sight, or is the result of the direct action of 

 light upon the integument. 



A FURTHER contribution to our knowledge concerning the 

 action of sunshine on microbes is to be found in a recent 

 number of the Comptes Rendiis (vol. cxviii. p. 151). MM. 

 d'Arsonval and Charrin find that if the b. pyocyanetis (an 

 organism frequently found in the pus from wounds) is exposed 

 to sunshine in culture liquid (presumably broth) for from three 

 to six hours, it is deprived of its pigment-producing power ; if, 



j however, it is only subjected to the influence of the red va.ys in 

 the spectrum, it exhibits subsequently the typical fluorescent 

 green colour on cultivation in agar-agar at 37° C. Moreover, if 

 the amount of sunshine it receives is extended, no growths at all 

 subsequently make their appearance, showing that it has been 

 destroyed ; whilst it can tolerate a similar exposure to the red 



' rays without exhibiting any signs of discomfort. This loss of 



' pigment-producing power may also, these investigators state, be 

 brought about by subjection to very low temperatures ; thus at 

 between - 40° and - 60° C. this bacillus loses its characteristic 

 rod-like shape, frequently becoming ovoid ; it multiplies very 



1 slowly, and exhibits only creamy white growths on agar-agar. 



i 



We have received a volume containing statistics of the colony 



I of Tasmania for the year 1892, compiled in the office of the 



[ Government Statistician from official records. 



