i8 



NA TURE 



[November 30. 1899 



Leguminous plants, whether first used as fodder for animals 

 or simply left to decay in the soil, have their albumen changed 

 in the first instance to amides, which under the influence of 

 ammonia-ferments are decomposed with formation of ammonium- 

 carbonate. The saltpetre bacillus then converts the ammonium- 

 carbonate (and probably also amides) into saltpetre, i.e. into 

 the best form of nitrogen plant-food. 



Unfortunately the whole of the nitrate thus formed is never 

 available for plants, on account of the destructive action of the 

 nitrate-destroying bacilli, which decompose the nitrates with 

 evolution of free nitrogen, and so complete the nitrogen cycle. 



The nitrate destroyers are usually present in stable-nianure, 

 and cause a deplorable loss to agriculture, amounting in 

 Germany to a sum of several million pounds annually. 



Efforts which, as Prof. Maercker assured the German Chemical 

 Society, are likely to meet with success at an early date, are 

 being made to avoid this loss ; and for this purpose special 

 bacteriological investigations are now being conducted at many 

 agricultural stations in Germany. 



UNIVERSITY AND EDUCA TIONAL 



INTELLIGENCE. 



■ Cambridge. — Dr. Langley, F.R.S., has been appointed 

 Chairman of the Examiners for the Natural Sciences Tripos. 



Mr. E. A. N. Arber, of Trinity, has been appointed Demon- 

 strator in Paleeobotany. 



Mr. W. F. Cooper, of Clare, has been nominated to the 

 occupation of the University table in the Naples Zoological 

 Station. 



Mr. H. H. W. Pearson, of Gonville and Caius, and Mr. 

 J. Barcroft, Fellow of King's, have been awarded the 

 Walsingham medals for research in botany and in physiology, 

 respectively. 



The degree of Master of Surgery was on November 23 con- 

 ferred on Mr. Timothy Holmes for his distinguished contributions 

 to the art and science of surgery. 



Sir Ernest Clarke has been re-appointed Gilbey Lecturer in 

 Agricultural History and Economics for the ensuing year. 



Prof. Woodhead, and Drs. Anningson, CoUingridge, Notter, 

 and Stevenson, have been appointed Examiners in State 

 Medicine. 



Dr. Somerville, Professor of Agriculture, has been elected a 

 Fellow of King's College. 



The Lawrence Scientific School of Harvard University has 

 received a gift of twenty thousand dollars to be used to equip 

 the mining and metallurgical laboratories. 



Dr. Paul Staeckel, assistant professor of mathematics at 

 Kiel, has been appointed professor ordinarius. Dr. J. Traube, 

 privatdocent in physical chemistry at the Berlin Technical High 

 School, has been appointed professor. 



The new leather industries buildings in connection with the 

 Yorkshire College, Leeds, which have been erected by the 

 Skinners' Company of London at a cost of 5000/., were opened 

 on Monday by the Master of the Guild, Mr. J. Colman. In 

 addition to the gift of the buildings the Company has granted 

 an endowment of 250A a year for ten years, thus placing the 

 instruction in the branches connected with the leather industry 

 on a solid foundation. 



The Canadian Educational Review announces that Sir W. C. 

 McDonald, of Montreal, whose magnificent gifts to McGill 

 University have made him justly celebrated as a public bene- 

 factor to education in Canada, has placed in the hands of Prof. 

 Robertson, Dominion Agricultural Commissioner, sufficient 

 funds to establish for three years technical schools in various 

 centres throughout the Dominion. The nature of the plan is to 

 take one city or town in each province in which to establish 

 regular classes in some of the ordinary schools on one or two 

 days a week, in which scholars between nine and thirteen years 

 of age shall spend a portion of the day in actual work with 

 tools. This will be supplemented whenever desired by more 

 advanced and special evening classes in manual training and 

 technical instruction. 



A COPY of the Magnet, the magazine of University College, 

 Bristol, has been received. There are several noteworthy ar- 

 ticles and items of information in the magazine, not the least 



NO. 1570, VOL. 61] 



interesting being the editorial note on the appointment of Dr. 

 Ryan, professor of engineering, to the principalship of the 

 Woolwich Polytechnic. Dr. Ryan has been at the College for 

 fourteen years, and has devoted his best energies to bringing 

 the engineering department to its present satisfactory position. 

 He would have done much more if the funds at his disposal 

 had permitted him to develop the work of the department ; but, 

 unfortunately, the College possesses only a small endowment, 

 and Bristol manufacturers are not so actively interested in the 

 progress of their University College as are many commercial 

 men in Liverpool, Birmingham, and other cities. Leaving this 

 point, attention may be called to an article in the Magnet on 

 life in a mediteval university, by Dr. Hastings Rashdall. The 

 description of the ceremonies through which the freshman or 

 bejannus of the middle ages had to pass before he could call 

 himself a student of the university would suggest many compari- 

 sons to an ethnologist. It must be remarked that the periodical 

 does not show the signs of active interest in scientific work which 

 are given in the form of notes and articles in some other magazines 

 of the same type. 



SOCIETIES AND ACADEMIES. 

 London. '' 



Physical Society, November 24.— Prof. G. Carey Foster, 

 F.R.S., Vice-President, in the chair. — A paper on the 

 conductivities of certain heterogeneous media for a steady 

 flux having a potential was read by Dr. C. H. Lees. 

 Two formulae have already been proposed to express the 

 conductivity of a mixture in terms of the conductivities 

 of its constituents. In the first formula the conductivity 

 is represented as the sum of a number of terms, each one of 

 which is the product of the conductivity of any constituent and 

 the fractional part of the mixture which is made up of that 

 constituent. In the second formula the resistivity of a mixture 

 is expressed in the same way with respect to the resistivities 

 and percentages of its constituents. In general, the first of 

 these suppositions gives results which are above the experimental 

 values, while the second gives results which are below. If we 

 suppose that the mixture is malie up of a series of columns of 

 the separate parts stretching normally between two equipotential 

 surfaces, then the conductivity would be accurately represented 

 by the first formula. If, however, we assume that the con- 

 stituents are arranged in parallel layers, then the second formula 

 would apply. In the present paper the author has attacked 

 the problem two-dimensionally, and has investigated the relation 

 which holds between the conductivities, when the constituents 

 are arranged in the mixture alternately like the squares on a 

 draughts board. Dealing first with two components it is easily 

 shown that the problem reduces itself to finding the form of the 

 equipotential curves and of the stream lines in a square which 

 is divided by a diagonal into two parts of different material. 

 By means of conformal representation Dr. Lees has referred 

 the square under consideration to a kite-shaped quadrilateral with 

 two opposite angles right angles, and the other two so deter- 

 mined by the conductivities of the constituents as to give 

 straight equipotential lines in the two portions of the figure 

 which represent the two materials and which are separated the 

 one from the other by the axis of symmetry. The general 

 relation which exists between the vector co ordinates in the 

 two systems has been proved by Love to consist of elliptic 

 functions ; but near the angular points of the figures a close 

 approximation can be obtained by the use of a simple 

 exponential expression. Talcing the known solution to the 

 problem in the case of the kite-shaped quadrilateral, it is 

 easy to calculate the result for the square under consideration. 

 This leads to the conclusion that the conductivity of the square 

 is the geometric mean of the conductivities of the constituents. 

 Allowing the medium to become fine-grained and introducing 

 new materials, it follows at once that the logarithm of the con- 

 ductivity of a mixture is equal to the sum of a number of 

 terms, each one of which is the product of the logarithm of the 

 conductivity of any constituent and the fractional part of the 

 mixture which is made up of that constituent. By a super- 

 position of fluxes, the author has shown that the above law 

 holds for flows in four directions, and he therefore considers 

 that with the assumed structure the formula represents the con- 

 ductivity for any flux. — Dr. Lees then read a second paper on 

 the thermal conductivities of mixtures and their constituents. 



