1 88 



SCIENCE-GOSSIP. 



CONDUCTED BY JAMES QUICK. 



Physics at British Association. — One of the 

 evening discourses at the recent meeting of the 

 British Association at Dover, was given, on Sep- 

 tember iSth, by Professor J. A. Fleming, upon 

 " The Centenary of the Electric Current," and was 

 illustrated by many successful and interesting experi- 

 ments. It is just one hundred years ago, since Volta, 

 of Como, invented the instrument which gave us the 

 first practical means of generating a continuous 

 electric current. Volta showed that if two pieces of 

 different metals were placed in contact and then 

 separated they were found to be at different electrical 

 potentials. Starting from this primitive but impor- 

 tant discovery, Professor Fleming veiy ably traced the 

 history of the production of the electric current down to 

 the present da)'. It is here, when one contrasts the capa- 

 bihties of the simple voltaic cell with the huge, powerful 

 dynamos now working in the numerous central 

 electric light stations, that one sees more clearly the 

 enormous strides made in electricity during the 

 present century. Passing through the stages of Volta's 

 " Couronne de Tasses," in which the two metals are 

 separated by a conducting liquid. Professor Fleming 

 led up to Cavendish and Faraday. By them and by 

 Oersted and Ampere an enormous advance was made 

 in electricity in discovering the important part played 

 by the medium or "dielectric" surrounding the wire 

 carrying the current and in showing the intimate con- 

 nection betvC'een electricity and magnetism. Electro- 

 magnetic induction, resulting in the dj'namo electric 

 and other machines, so e.xten.sively used all over the 

 world at the present day, may be said to have begun 

 its life with the researches of Faraday and Ampere. 

 Some brilliant experiments were shown illustrating 

 induction, which brought the lecturer to the interest- 

 ing topic of signalling through space by induction, or 

 as it is more generally termed, " wireless telegraphy." 

 No doubt the reader is acquainted with some of 

 Marconi's successes, achieved in carrying out his 

 method. A good example of its capabilities was 

 given by Professor Fleming during his lecture. A 

 message was sent from the instrument upon the 

 lecture table to the receiving instrument at Wime- 

 reux, upon the French coast, and then conveyed by 

 telephone to the President of the French Association 

 for the Advancement of Science, at Boulogne. The 

 reply was conveyed back by the same method and re- 

 ceived by Professor Fleming a short interval after- 

 wards. It was not only at Professor Fleming's 

 lecture that experiments with Marconi's signalling 

 apparatus were successfully performed. On the i6th 

 and 1 8th of September messages were also conveyed 

 via Wimereux, to and from the President of the 

 Electrical Congre.ss then hieing held at Como, Italy — 

 Volta's birthplace. As regards other Physics work 

 done during the British Association meeting there is 

 no doubt that the absence of some leading 

 physicists was due to the Volta ' Congress at 

 Como, and to the Switzerland meeting of the 

 Institution of Electrical Engineers, both taking place 

 at about the same time. After Prof. Poynting's 

 presidential address before Section A (Mathematics 



and Physics), on September 14th (S.-G., p. 151), 

 came an important paper read by Mr. G. J. Burch, 

 M.A., entitled "The Spectroscopical Examination 

 of Contrast Phenomena." The two theories of colour 

 vision to the fore at the present day are the Young- 

 Helmholtz theory, which supposes there are three 

 primary colours, red, green, and violet ; and Ilering's 

 theory demanding only two. Mr. Burch's experiments 

 have led him to the conclusion that blue is also a 

 primary colour ; that we have, in fact, separate 

 primary sensations both for blue and violet, besides 

 those for red and green. Mr. Burch thus supports 

 the three-colour theory, but with this modification. 

 On the other hand, Hering's theory requires that red- 

 blindness should be accompanied by green-blindness ; 

 but Mr. Burch finds it need not be so accompanied. 

 His experiments show that if the eye is fatigued by 

 exposure to a very intense red light and a spectrum 

 be then looked at, the red is invisible, but the 

 remainder of the spectrum, from green to violet, 

 appears in its ordinary colours. To avoid all errors 

 due to pigment colours, the above experiments were 

 carried out with spectral colours. It will be interest- 

 ing if other experimenters, working upon similar 

 lines, obtain the same results to those of Mr. Burch. 

 On Saturday, September i6th, when .some members of 

 the French Association were present. Prof J. J. 

 Thomson communicated a most important paper 

 bearing upon the question whether the atoms 

 of matter, a,s we now consider thenr, are not capable 

 of sub-division. The three principal lines along 

 which this question may be attacked are, electrolysis, 

 the velocity of charged particles in a magnetic field, 

 and the magnetic deflection of kathode rays. From 

 Prof Thomson's experiments he considers that 

 electrification consists in the removal from the 

 " atom " of a small corpuscle with which the negative 

 charge is associated, the remaining portion of the atom 

 being positively charged. An important discussion 

 upon platinum thermometry was opened by Prof. 

 Callendar, who suggested the adoption of the variation 

 in the resistance of platinum as a basis for a practical 

 scale of temperature. Prof. Carey Foster was of 

 opinion, however, that for absolute values the gas 

 thermometer must be used, because we have no theory 

 of the variation of resistance with temperature. Dr. 

 Chree also said that some platinum Ihermonieters 

 purchased by the Kew Observatory had worked in a 

 peculiar manner and were not satisfactory. Principal 

 Glazebrook suggested that before accepting platinum 

 as a standard, experiments should be made to ascertain 

 whether other metals — such as gold, were more 

 efficient. Mr. Alexander Siemens, M. Inst. C. E., 

 reviewed the application of electricity to machinery 

 used in ships ; and the more recent improvements, 

 such as substituting electric motors for small engines 

 distant from the boilers, by this means much steam- 

 piping with consequent leakages is avoided. 



Refractive Indices of Chloride Solu- 

 tions. — In the Royal Society Proceedings 64, an 

 account is given of the determinations of the refractive 

 indices and densities of solutions of various chlorides. 

 From these observations it appears that both the 

 densities and the refractive indices increase with the 

 molecular weight of the substance in solution. An 

 exception occurs in the case of the refractive index of 

 potassium chloride, which is slightly lower than that 

 of sodium chloride. In these experiments a hollow 

 prism was used, and filled with the solution in 

 question, care being especially taken to keep it at a 

 temperature of iS" C, as the slightest variation was 

 found to make a considerable difference in the final 

 values obtained. 



