644 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



strong lever H, and clicks in three resting-spots. At the centre of one 

 of these spots the two teeth z of the cog-wheel lying behind the lever H 

 are released, so that H goes out of gear. When F is moved to the right 

 spot, the object is also moved to the right through a distance of the field- 

 diameter. When F is moved to the left resting-spot, the object is 

 similarly moved the distance of a diameter to the left. The apparatus, 

 it will be observed, bears some resemblance to Engel's mechanical stage, 

 as made by Leitz. But the distinctive peculiarity of the perquirator is 

 that its movement is adjusted for a diameter of the new field. Fig. 107 

 shows the perquirator in plan. Fig. 108 shows it in lateral elevation. 



WMMMM&-'M^h^ m 



Fig. 108. 



New Method of Measuring Hardness.* — V. Poschl has devised a 

 combination of sclerometer and Microscope for the purpose of measuring 

 hardness with more precision than is possible by the ordinary methods. 

 His sclerometer (fig. 109) consists of a zinc plate on three levelling 

 screws, and a circular level is attached to the plate. When the plate is 

 level the axis of a certain lever is also horizontal. This lever carries at one 

 end the scratching-point surmounted by a scale-pan for receiving any 

 suitable weight. A pointer attached to the lever-axis works on a gradu- 

 ated arc (something like the pointer of a balance), and insures that the 

 lever remains at a constant inclination. The beam carrying the lever 

 slides up and down in a hollow vertical pillar attached to the zinc plate, 

 and can be clamped at any required height. The crystal, or other hard 

 body to be tested, is set, so as to have the tested surface horizontal on a 

 specially designed bearer. This bearer rests on a carriage working on 

 three runners attached to the zinc plate. A cord running through a system 

 of pulleys pulls the carriage with the bearer and crystal across the zinc 

 plate, and so brings the crystal into contact with the scratching-point. 

 Although there are other methods of estimating hardness, the author 

 considers that it should be taken as proportional to the weight pressing 

 upon the scratching-point. 



Next, it is necessary to examine microscopically the breadth and 

 depth of the scratch upon the crystal, and hardness is now considered to 

 be inversely proportional to the size of the furrow. The instrument 

 used was Reichert's Metall-mikroskop, as designed by Rejto. It was 

 combined with the sclerometer in such a way that the crystal, after being 



* Zeitschr. wiss. Mikrosk., xxvi. (1909) pp. 104-10 (1 fig.). 



