146 Transactions of the Society. 



III. — On an Improved Form of Metallurgical Microscope. 

 By Walter Kosenhain, B.A. (Cantab), B.C.E. (Melbourne). 



{Bead February 21, 1906.) 

 Plate VI. 



The importance which the microscopic study of metals has steadily 

 acquired during the past ten years has led to the development of 

 a special form of Microscope suited for the requirements of this 

 class of work ; the development of these instruments has, however, 

 been almost entirely confined to progressive modifications of the 

 standard type of Microscope as used for other purposes. While it 

 is undoubtedly possible to obtain very satisfactory results in the 

 study of metals by means of a good Microscope of the ordinary 

 type, provided with certain special attachments, limitations and 

 disadvantages soon become evident, and even the most specialised 

 metallurgical Microscopes hitherto available do not overcome the 

 most serious of these difficulties. On the other hand, as the author 

 has endeavoured to show elsewhere,* the design of the standard 

 Microscope does not, in certain respects, satisfy the demands of 

 correct mechanical design ; and while it may, perhaps, be fairly 

 urged that the optical requirements necessitate the sacrifice of 

 mechanical perfection, such a contention does not apply to the 

 metallurgical Microscope, which is intended primarily for the 

 examination of opaque objects by reflected light. These considera- 

 tions have led the author to design the instrument here to be 

 described, on lines which differ very considerably from those of the 

 standard type of Microscope. 



The main differences between the requirements of the ordinary 

 Microscope and the instrument intended for metallurgical purposes, 

 arise from the fact that the apparatus for the use of transmitted 

 light, which is so important in the former, is not required at all in 

 the latter, while, on the other hand, the appliances known as ver- 

 tical and oblique illuminators are essential for metallurgical work, 

 and are rarely used for other purposes. Further, the specimens to 

 be examined with the metallurgical instrument are sometimes of 

 considerable weight and size, and it may be desirable to examine 

 them by means of long-focus lenses (3-inch), so that a very wide 

 range of separation between stage and objective is required. In 

 the older metallurgical Microscopes this last requirement has 



* "The Mechanical Design of Instruments," by W. Rosenhain, Proc. Optical 

 Convention, London, May 1905. 



