December i, 1910J 



NATURE 



149 



of 21 metres in long. 139° 45' E., lat. 35° 41' N., and was 

 rebuilt in July, 1897, great care being taken to exclude 

 magnetic ingredients from the materials employed. The 

 present valuable report gives a brief description of the 

 building and apparatus, and also describes the methods 

 employed in registering the different variations of the 

 magnets. A number of tables give the hourly values, for 

 the whole year, of the three elements, with remarks as 

 to the nature of the variations, indicating storms, &c. A 



evere storm " was registered during the morning of 



bruarv 10, 1907, the magnets having been agitated 

 during the preceding three days. The principal disturb- 

 ances are shown on fourteen large-scale charts given at 

 the end of the report. 



The first part of vol. ii. of the Transactions of the 

 Royal Society of South Africa includes a paper by Dr. 

 .A. W. Roberts on a preliminary determination of the 

 absorption of light by the earth's atmosphere. The paper 

 is a brief statement of a single determination of the 

 coefficient of atmospheric absorption made on the summit 

 of one of the hills of the Winterberg Range, of an altitude 

 of about 4000 feet. More than 500 observations were 

 made, and it was hoped at first that these observations 

 would yield both the coefficient of absorption and the 

 height of the atmosphere, but a variety of solutions con- 

 firmed Dr. Roberts in the view that a more refined series 

 of observations would be necessary before any trustworthy 

 value of the height of the atmosphere would emerge from 

 the equations. Dr. Roberts obtained as a final value for 

 the coefficient of atmospheric absorption at sea-level 

 0-19 m, where ni is the apparent magnitude of a star. 

 The mean of the results obtained by Seidel, Langley, 

 Pritchard, Muller, and Pickering is 021 w. Taking 

 0-20 m as a mean result. Dr. Roberts points out that 

 this signifies that 17 per cent, of all rays that strike the 

 atmosphere perpendicularly are absorbed by the atmo- 

 sphere. On the horizon the brightness of a star is reduced 

 so that it shines with only about one-fortieth of its zenith 

 •brightness. 



Prof. Edgar Bcckingham contributes to the Bulletin 

 of the Bureau of Standards, vi., 3, a short note on the 

 definition of an ideal gas, embodying a brief statement 

 of the main principles of thermodynamics associated with 

 fhe definition in question. 



On February 21, 191 1, the well-known firm of publishers 

 iuunded by Benedikt Gotthelf Teubner will celebrate its 

 centenary. In this connection a catalogue has been issued 

 of recent works published by Messrs. Teubner dealing with 

 scientific subjects, which affords a striking example of the 

 influence which private enterprise can bring into play in 

 the advancement of learning. Moreover, the list only 

 deals with a small portion of the Teubner publications, 

 separate catalogues being issued for literary and other 

 subjects. 



In the Rendiconto of the Naples Academy, 5, 6 (May 

 and June), Dr. Paolo Rossi describes observations on the 

 double refraction induced by strain in caoutchouc. The 

 principal conclusions appear to be that the difference of 

 the principal indices of refraction is proportional to the 

 tension, that the results are pretty much the same for 

 vulcanised and unvulcanised caoutchouc, and that when the 

 elongation is maintained constant the double refraction 

 maintains its proportionality to the tension, even though 

 the latter gradually decreases. 



The action of light on plants forms the subject of a 

 note in La Nature for October 20 by M. H. Rousset, 

 dealing with some recent experiments by M. Combes. 

 The author points out that the effects of light vary accord- 



NO. 2144, VOL. 85] 



ing to the age and nature of the plant, a strong light 

 favouring the development of large stores of reserve 

 material, as in the tubers of the potato and in the beet, 

 while a weaker light favours the growth of vegetative 

 organs. The effect of light on the ova of trout is studied" 

 by Prof. Felice Supino in the Rendiconti del R. Istitut(y 

 Lombardo, whose experiences tend to show that blue light 

 is more favourable to the hatching and development of the 

 ova than red. 



In the Rassegna contemporanea for October (a journal 

 which, by the way, has during the past few months con- 

 tained a number of well-written articles dealing with 

 English national movements), Signor Gino Cucchetti 

 publishes an article dealing, as the author claims, with a 

 suggestion by the geologist, Venturino Sabatini, accord- 

 ing to which a remedy for the disastrous effects of earth- 

 quakes in Messina and southern Italy should be sought 

 in an efficient scheme of afforestation. It is pointed out 

 that the cutting down of trees in such districts may fre- 

 quently result in a loosening of the subsoil, which is 

 largely argillaceous or sandy in character, thus giving rise 

 to faults and lessening the resistance to the effects of 

 seismic disturbances. The cutting down of woods receives 

 further mention in an article by the deputy Giovanni 

 Posadi dealing with the preservation of natural beauties, 

 while an article by Signor Arnoldo Faustini dealing with 

 changes that have occurred on the earth's surface in recent 

 times, with special reference to the subsidence of the 

 island of Bogoslaw, in .Alaska, possesses collateral interest 

 in the same connection. 



The report on the work of the Government Laboratories, 

 Johannesburg, for the year 1908-9, has recently reached 

 us. Whilst pointing to excellent services in the past, it 

 gives evidence of the need for further inquiry into and 

 control over the food and water supply of the district. 

 The total population of the colony is about one and a 

 quarter millions, including 300,000 persons of European 

 descent ; but only 158 samples of foodstuffs other than 

 milk were examined during the year. This, as the 

 analyst remarks, is very inadequate surveillance. As 

 regards the water supply, that of Johannesburg was well 

 looked after both chemically and bacteriologically ; and 

 that of Pretoria, where excellent water is obtainable, was 

 also examined, though by bacteriological methods alone. 

 But spasmodic attempts only have been made to control 

 the condition of any of the other supplies of the colony 

 by scientific means, and no proper systematic water survey 

 has yet been made. Among other matters, it is noted that 

 out, of a total of 8526 samples examined, more than three 

 thousand, mostly rats, were dealt with in connection with 

 plague investigations. 



The contradictory results which have been obtained as 

 to the effect of a magnetic field on the potential difference 

 necessary to cause a discharge to pass between two elec- 

 trodes in a rarefied gas are explained in a paper by Prof. 

 Righi communicated to the Academy of Science at 

 Bologna in May, and reproduced in the October number 

 of Le Radium. The electrodes were about 2 square cm. 

 in area and from 0-5 to 8 mm. apart, the gas having a 

 pressure of a few tenths of a mm. of mercury. The 

 difference of potential was provided by small storage 

 cells, and the current transmitted measured by a galvano- 

 meter. The magnetic field in which the discharge tube 

 was placed could be raised to 9000 units. Prof. Righi 

 finds that the effect of the field, for strengths up to about 

 1000 units, is to diminish the required potential, but for 

 greater strengths to increase it, and in the case of trans- 



