TROWBRIDGE & CrANDaXI.. 



Phil. Mag. Ser. 6. Vol. 22, PL IX. 



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WOOD GRATING No. 7. 



GRATING SPACE: 00123 cm. 



ANGLE BETWEEN COLLIMATORS: 19 " 2. 

 Form of Groove as in Fig. 4 (Text). 



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