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SUMMARY OF CURRENT RESEARCHES RELATING TO 



of the centre of gravity in clianging the inclination of the instrument, 

 so that great stability in all positions is secured, and the optical 

 centre is thus made the centre of all the circular motions of the parts 

 of the instrument. 



The first application of the sliding motion of the body was made 

 by Geo. Wale in his 'Working Model,' but he did not make the 



Fig, 29. 



centre of motion the optical centre of the instrument. Mr. Wenham 

 in his elaborate concentric Microscope uses a separate rocker arm 

 with the whole body of the ordinary instrument pivoted above it. 

 My design, which has been constructed by the Bausch and Lomb 

 Optical Company, greatly simplifies the Wenham instrument, and 

 extends the principle contained in Wale's, and makes a very compact, 



