HIGH MAGNIFICATION MICROGRAPHS 187 



Fig. 6 reproduces a micrograph obtained with a platinum layer 

 of a definite thickness, scarcely providing any appreciable increase 

 in light intensity; exposure 20 sees., as in the other cases. A 

 somewhat thinner coating might have been desirable. 



It is of interest to note, however, that the micrographs obtained 

 in this way were characterised by an unusually large extension of 

 the sharp image. The contrasts seem to be somewhat weaker than 

 those obtained with the other illuminators, and possibly this is the 

 reason why on Fig. 5 (in original) are to be seen details, e.ff., some 

 characteristic irregularities in the ferrite ground mass, which scarcely 

 are to be seen on any other of the micrographs taken. 



Thus it was found from these experiments that any essential 

 gain in light intensity is difficult to obtain by platinum coating, 

 but on the other hand a more detailed investigation is required to 

 find out whether the filtering of the light on passing through the 

 thin metal coating might possibly be of some advantage when it 

 is a question of bringing out a maximum of detail. 



11. Further remarks. 



It has to be added that every exposure w^as repeated several 

 times, and found consistent with similar experiments, so that, not- 

 withstanding the obvious difficulty of avoiding focussing errors, the 

 results obtained appear to be quite reliable. 



A detailed account of these investigations has been published in 

 Swedish in Biharig till Jernkontorets Annaler, Vol. 19, p. 537, 1918. 



A detailed account will also probably appear in Zeitscfirift fur 

 Wissenschaftlich e Mikroskopie . 



Summary. 



The investigations were started as a detailed and critical ex- 

 amination of the new Reichert microscope, which is of the Le Cha- 

 telier type. It was found to produce excellent results at the very 

 highest magnifications. 



Then some points of a more general character were examined, 

 as: 



(1) The using of an arc lamp (350 c.p.) or of an incandescent 

 lamp (50 c.p.) gave exactly the same result. 



(2) A modification of the microscope is proposed in order to 

 diminish its vibration sensitivity. 



(3) The proper arrangement of the diaphragms is discussed. 



(4) A Le Chatelier prism and a 45° prism give at high magnifi- 

 cation exactly the same result. 



(5) A metal mirror gives slightly better contrasts than a prism. 



(6) In the plain glass illuminator a thickness of 0.45 mm. does 

 not injure sensibly the image quality. 



(7) A slightly platinised glass illuminator gave somewhat finer 

 details than any other illuminator used; this question, however, 

 needs further research. 



