VI 



Proceedings. {October sth, i8gj. 



97- 8" 



Fig. 6. 



Numerous examples of its use can be given, but the foregoing 

 will serve to show the use to which the instrument can be put, 

 and although its indications will not suffice where great accuracy is 

 required still the results are very satisfactory, and in any case I 

 cannot but think that it will prove of some educational value in 

 affording a better insight into the principles underlying refraction 

 than can be obtained from the usual geometrical constructions. 



Professor Lamb mentioned Sir George Airey's model illus- 

 trating the refraction of light, and Dr. Lees and Mr. C. L. Barnes 

 took part in the discussion of the instrument and the geometrical 

 construction which it is designed to illustrate. 



