proceedings: philosophical society 129 



Then d = M+N (^-^A 2 ). A table of the complex factor, call it 



n', is easily computed from Barlow's Tables of Squares and Recipro- 

 cals if b, c, and d are taken equal to 0.01, as they are approximately 

 for quartz. But the same table of values of n' will fit values of X in- 

 creased or decreased by as much as 30 ju/z, which is ample to allow three 

 comparison wave-lengths in a spectrogram to be brought into coin- 

 cidence with the curve. Other wave-lengths are then interpolated 

 by d = M + Nn.' The paper was discussed by Mr. Burgess. 



Mr. P. D. Merica then presented an illustrated paper on Some 

 metallographic methods. The term metallography connotes in its gen- 

 eral sense the study of the structures of metallic substances and the 

 properties of these substances as related to structure ; it has often been 

 confused with the microscopic study of metallic substances, which is 

 really only one phase of metallography. Slides were shown to illus- 

 trate the crystalline structure and growth of metals and alloys. De- 

 fective materials are often to be detected by microscopic examination, 

 such as, for example, the presence of slag or oxide, the application of 

 improper heat treatment, etc. The method of thermal analysis is used 

 to determine the melting points and transformation temperatures of 

 metals and alloys ; it has been used to detect the presence of impurities 

 in metallic tin, for example, the presence of 0.3 to 0.5 per cent of zinc. 

 Initial stresses are found in most metallic materials, due to unequal 

 rate of cooling or working; it has been shown that these are often re- 

 sponsible for failures of materials, for example, in the case of brass rods 

 and tubes. A method for determining structural identity or differ- 

 ence according to Hanemann was described. The theories of plastic 

 deformation of metals were discussed and evidence described bearing 

 upon these theories. In conclusion a plea was made for a fuller de- 

 scription of metallic materials used in determinations of constants. 

 The paper was discussed by Messrs. White and Tillyer with reference 

 to methods of getting wire of certain properties for thermo-elements. 



The 764th regular meeting and 45th annual meeting of the Society 

 was held at the Cosmos Club, December 11, 1915. Vice-President 

 Briggs in the chair ; 33 persons present. The minutes of the 44th Annual 

 Meeting were read. 



The report of the Secretaries was read by Mr. Fleming, showing an 

 active membership of 149. Sixteen regular meetings have been held. 

 The report was ordered accepted. The Treasurer's report through 

 December 9, 1915, was read by Mr. Sosman. The total receipts for 

 the year were $1075.09; total expenditures, $1420.09, including pur- 

 chase of bond of par value $500; total investments, $12,000; cash in 

 hand, $109.72. The report of the Auditing Committee consisting of 

 Messrs. Kimball, Ferner, and Wallis was read by Mr. Kimball. This 

 Committee reported the statements in the Treasurer's report to be 

 correct. The report was ordered accepted and to be filed with that 

 of the Treasurer. The Treasurer's report was ordered accepted. 



