MICROSCOPE: HEKMAN A. HOLZ 193 



ported stage below the objective, thus permitting the convenient 

 investigation and photography of heavy specimens, observation of 

 their edges, use of daylight, and large reduction of vibrations. 

 While these outfits are not available any longer, it seems to me 

 that the development of satisfactory photomicrographic apparatus 

 for metallography should follow this general design, and not the 

 inverted design, which possesses several disadvantages more impor- 

 tant than its one single advantage. 



Amongst other microscopic problems awaiting further develop- 

 ment, besides higher magnification, are: the utilisation of polarised 

 light for metallographic investigations and the application of kine- 

 niatographic work to the study of structural changes in metal 

 sections exposed to mechanical stresses or varying temperatures. 

 The pioneer work in solving the apparatus development problems 

 for these studies has been successfully carried out, and the high 

 value of such investigations will be appreciated. It is to be hoped 

 that research workers will take up systematically this work, which 

 has been successfully started. Further microscope development, 

 offering no more difficulties, will be in the direction of stereoscopy. 

 We are born with two eyes, and used to see with both of them; 

 mon-objective binocular microscopes, for work with the highest mag- 

 nifications, have been successfully developed, and there seems to be 

 no reason why this instrument development should not be applied 

 to advantage to metallographic practice. I believe that the near 

 future will see a large extension in the use of binocular optical 

 instruments. 



I would not like to omit here to mention some important pro- 

 gress made in Great Britain in the development of metallographic 

 equipment: The Edison-Swan " Pointolite " (tungsten arc) lamp, 

 which is the ideal source of light for photomicrographic work, and 

 the Wratten and Wainwright light filters and special plates for 

 photomicrography. These products represent the best that has ever 

 been developed in their respective lines, and every metallographer 

 will find the use of these appliances extremely valuable in his work. 



In ending my contribution, I want to make a few additional 

 remarks about the importance of " magnetic analysis " in metallo- 

 graphic research and routine work. The use of higher magnifica- 

 tions in microscopic investigation will most probably lead to valuable 

 results, although we must always remember that the higher we 

 magnify the less we see, i.e., the field of observation is getting 

 smaller with the use of objectives of higher powers. Magnetic 

 analysis (the accurate determination of the various magnetic proper^ 

 ties of iron and steel by means of a standard permeameter) enables 

 us to draw distinctions between steels where the present methods 

 (microscopic, hardness, tensile tests) fail to make differentiation. 

 Microscopic investigation of steel gives results which are qualita- 

 tive, rarely quantitative. The preparation of micro-sections often 

 releases stresses in the metal to be studied, and, in general, tests 

 of this kind require a great deal of individual judgment and experi- 

 ence. Magnetic data permit quantitative measurements of the state 

 of micro-structure and the interpretation of test data leaves no room 

 for conjecture. 



