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XXXVI. The Tangent Lens-Gauge. 

 By George J. Burch, M.A* 



THIS simple piece of apparatus, which for want of a better 

 name may be called the Tangent Lens-gauge, is intended 

 to afford an inexpensive means of measuring the radius of 

 curvature of convex lenses. 



It consists of two pieces of stout plate-glass about 4 cms. 

 wide, cemented with marine glue on to a third and larger 

 piece, as in the annexed figures. 



ZJ 



Side Elevation. 



Plan. 



End Elevation. 



A strip of ordinary window glass is placed under the 

 outer edge of each of the square pieces, so that they are 

 inclined at a small angle to each other, and they both project 

 equally beyond the end of the third piece. The lens to be 



* Communicated bv the Author. 



