SUGGESTED ALTERATIONS IN THE DESIGN OF THE 

 LE CHATELIER TYPE OF METALLURGICAL MICROSCOPE, 



By Professor F. Giolitti {Italy). 



It is well known that the principles laid down by Le Chatelier for 

 the design of his instrument have been applied, with different con- 

 structional details, by various Makers and it is also recognised that 

 the design of the Le Chatelier Microscope which has found greatest 

 favour is that adopted by Pellin of Paris and Dujardin of Diisseldorf. 



I have had long and practical experience of this latter type of 

 design, and I do not think I am wrong in stating that, even though 

 the Le Chatelier Microscope offers the best solution of problems 

 connected with the microscopic examination of metals, and is much 

 preferable to all similar types of apparatus on the market, it has 

 two disadvantages, which, however, are quite easy to rectify by 

 means of some simple modifications in constructional detail. 



The first of these disadvantages consists in the fact that the rack 

 which supports the stage is directly fixed " on one side " of the stage, 

 so that the weight of the stage and of the object placed upon it tends 

 to produce a sagging of the rack. 



This sagging effect becomes more and more pronounced as time 

 goes on, and prevents the focussing of the whole of the metallic section 

 under examination. It is intensified, and in a short time may seriously 

 damage the instrument when it is required to examine fairly heavy 

 specimens, and this is a case which frequently occurs in practice. 



The second disadvantage consists in the absence of an apparatus, 

 w^hich, like the revolving objective holder in the ordinary Microscope, 

 permits of rapidly and easily changing the objective. In the Le 

 Chatelier instrument, in order to change the objective, it is necessary 

 to raise the stage, unscrew the first objective, screw the second objective 

 into the place of the first, lower the stage, and refocus. This operation 

 is very long and tedious, and it is even more so when, with a view to 

 preventing the inconvenience of allowing the various objectives to 

 remain uncovered on the work table, it is necessary each time to put 

 back into its case the objective which has been removed from the 

 Microscope and take out of its box and fix on the instrument the new 

 one required. And, of course, it is often necessary to examine each 

 metallic section under various magnifications, in order to find out with 

 accuracy the true significance of the various structural elements, and 

 eliminate errors in the interpretation of the structure. 



For these reasons I have studied, with the help of Dr. A. Filippini 

 of Genoa (to whom I extend my heartiest thanks for his valuable 

 collaboration), a type of Microscope which, while still preserving the 

 -extremely useful fundamental principle of the " vertical " observation 

 which makes the Le Chatelier Microscope so practical, gets over the 

 disadvantages to which I have referred. 



The new Instrument differs from similar apparatus principally 

 by the addition and different arrangement of a few of the external 

 parts, which are clearly shown in the illustration. Fig. I. 



I will, therefore, only refer very briefly to the features of these 

 parts, without touching upon anything regarding the other components 

 of the Microscope — such as method of illumination, system of pro- 

 jection, etc. — which do not differ essentially (except for the special 



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