540 



SCIENTIFIC NEWS. 



[Nov. 23, 1? 



up the old Lake Agassiz, and its effects upon agriculture. 

 He stated that good alluvial soil occurred along the North 

 Saskatchewan and Peace Rivers, districts which have a 

 great agricultural future. The Laramie coal occurs as 

 pure anthracite in the disturbed districts. He asked 

 whether the flora of a country was not of a later type than 



the fauna. 



PHYSICAL SOCIETY. 

 At the meeting held on November 10th, 1888, Pro- 

 fessor Reinold, President, in the chair, the following 

 communications were read : " On the Calculation of 

 the Coefficient of Mutual Induction of a Helix and 

 Coaxial Circle," by Professor J. V. Jones. In arrang- 

 ing some experiments for determining resistance abso- 

 lutely by Lorenz's method the author had occasion to 

 consider what form of standard coil was most suitable 

 for accurate calculation, and chose a helix of large 

 diameter, with a single layer of wire. To obtain a 

 sufficient number of turns requires considerable axial 

 length ; and Lord Rayleigh's approximate method of 

 calculating the coefficient was found to be insufficient 

 where an accuracy of 10s per cent, is required. A more 

 accurate method of calculation is given which, applied to 

 a circle of 10 ins. diameter, placed concentric with a helix 

 of 20 ins. diameterand 4 ins. long, yielded the value of M = 

 «. 53'259,whereasLord Rayleigh's formula gives n. 53'3i7. 



Professor Perry asked if the thickness of the wire had 

 been considered, and whether the author could give any 

 information as to practical working formulae for the 

 mutual induction between the ordinary cylindrical coils 

 in any position. 



Dr. Fleming described a wooden anchor ring wound 

 like a gramme armature, and having a secondary coil 

 added, which he had devised as a standard of mutual 

 induction, and used for determining capacity absolutely. 



In reply, the author said he had not considered the 

 wire to have thickness, as he felt sure this would not 

 affect the result for his coil by one part in 100,000. 

 With respect to Dr. Fleming's anchor ring, he considered 

 the difficulty of winding it sufficiently uniformly to be a 

 great drawback to its general adoption. 



A paper on "The Upper Limit of Refraction in 

 Selenium and Bromine," by Rev. T. Pelham Dale, 

 M.A., read by Mr. Baily. In a former communication 

 (read February nth, 1888) the author showed that an 

 upper limit of refraction for selenium should theoreti- 

 cally exist about the middle of the visible spectrum, and 

 the present communication describes some experiments 

 which tend to confirm the prediction. On placing a thin, 

 transparent film of selenium under a spectro-microscope, 

 it was found to be opaque to rays above the green, and 

 previous calculations had given 5295*7 as the limiting 

 wave length transmissible. 



Sulphur at ordinary temperature should have its upper 

 limit beyond the visible spectrum, but theory indicates 

 that increased temperature will lower the limit. It is 

 well known that sulphur darkens when heated, and when 

 a film of boiling sulphur was examined under the spectro- 

 microscope all but the red end of the spectrum was 

 absorbed. On cooling, the region of absorption gradually 

 retreated towards the violet end. 



Selenium is also found to become more transparent 

 as it is cooled, and its refractive equivalent is equal to that 

 of sulphur multiplied by the ratio of its chemical equiva- 

 lent to its density. Important optical, as well as chemi- 

 cal relations thus exist between the two elements. 



The results obtained by bromine films were re- 



markably similar to those of selenium, the violet rays 

 being entirely cut off. 



A method of solving the equation a sin = sin m 9 

 (on the limiting solution, of which the upper limit of 

 refraction depends) by a table of Eulerian integrals is 

 given in the paper, and an analogy between total reflec- 

 tion and the upper limit of refraction is traced. 



Professor S. P. Thompson, D.Sc, exhibited some 

 Experiments on Glass in Polarised Light. Irregular 

 pieces of glass can be tested for internal strain by 

 immersing them in a liquid of equal refractive power. 

 Various specimens of tubing, rod, and thermometer 

 tubes were examined in this way, all of which showed 

 defective annealing. One piece of ordinary rod bent 

 zig-zag produced remarkable effects when rotated in the 

 liquid. Prince Rupert's drops, a glass wedge, and a 

 model ol the " Regency diamond " showed vivid colours, 

 and the stems of broken incandescent lamps exhibited 

 various degrees of annealing. 



Mr. Hilger wished to know whether parallel plates 

 had been tested, and with what result, for he had always 

 found pieces of shapes approaching to roundness, to show 

 greater defects than parallel plates. For this reason he 

 always cut his prisms and lenses from rectangular blocks. 



Mr. Blakesley said that no perfectly annealed ther- 

 mometer had been shown, and he was anxious to know 

 whether any existed. 



Mr. Wilson expressed a doubt as to whether it was 

 possible to anneal anything so as to be perfectly free 

 from internal strain, and thought the act of breaking 

 rods and tubes necessarily introduces strains. 



Professor Rucker asked whether the usual method of 

 detaching a mercury column for calibrating thermo- 

 meters produced any injurious effect, but the author 

 was unable to speak decisively on the subject. 



In answer to the President, Dr. Thompson said the liquid 

 used was a mixture of carbon bi-sulphide and alcohol. His 

 experience with parallel plates coincided with that of Mr. 

 Hilger. As an example of the remarkable effects which 

 could be produced in glass by various methods of cooling, 

 he directed attention to the fact that Professor Esener, of 

 Vienna, had produced lenses having plain faces. 



Dr. J. A. Fleming, M.A., described a new form of 

 standard resistance coil. Considerable difficulty had 

 been experienced with coils of the ordinary B.A. con- 

 struction when immersed in water or melting ice, due to 

 leakage across the paraffin wax caused by condensation 

 of moisture. To overcome this, various forms have 

 been tried, and the best yet devised is made by winding 

 the coil in the space between two shallow annular 

 casings screwed together by projecting flanges. The 

 joint is formed by indiarubber, and can be tested for 

 leakage by immersing in water and applying air pressure 

 through a small testing-tube. The rising part of the 

 terminal rods are enclosed in long brass tubes soldered 

 to the upper casing and insulated by air, excepting at 

 the top and bottom, where ebonite rings are placed. The 

 top ring forms a corrugated cap, and an annular channel in 

 its upper surface serves as a fluid insulator. The wire, 

 which is triple silk covered, is baked for some hours at a 

 temperature above ioo° C, and then soaked in anhy- 

 drous paraffine wax containing about 3 per cent, of resin. 



ENTOMOLOGICAL SOCIETY. 

 At the meeting held on November 7th, 1888, Dr. D. 

 Sharp, F.L.S., President, in the chair, Mons. A. Wailly 

 exhibited a large and interesting collection of butterflies 



