THE WOODWARD ILLUMINATOR. 177 



the Wenham forms, and in the comparative examina- 

 tion of objectives, the wedge illuminator is an exceed- 

 ingly handy accessory. In the determination of the 

 collar adjustment corresponding to the point of maximum 

 aperture, the same holds true. 



We have spent two or three entire evenings in the at- 

 tempt to determine which of the two illuminators is the 

 most effective ; and our experience leads to the conclusion 

 that the " reflex " is somewhat the superior instrument 

 in the resolution of the most difficult lined tests; never- 

 theless, we are glad to give the newcomer a place in the 

 accessory box, and expect to make it very useful. It is 

 easily made and mounted, and ought not to be expensive. 



Another matter closely allied to the new illuminator 

 may as well be mentioned here. Learning that the 

 Messrs. Spencers had just completed a new one-fourth 

 inch objective, which was to be sent to the Paris Expos- 

 ition, we wrote to these gentlemen asking the loan of 

 the glass for examination, the Messrs. Spencers re- 

 sponded promptly, and it occurred that we received 

 the one-fourth and the new illuminator the same day. 

 We were thus enabled to put the illuminator to practi- 

 cal use at once, in this manner: First, we took our one- 

 sixth, working it with the illuminator over the No. 20 

 of the Moller plate getting the radial bar as far from 

 axis as the objective would allow and preserve a good 

 display of the striae. This done, we substituted the 

 one-fourth in place of the one-sixth, keeping the illum- 

 ination, etc., carefully in the same position, (the cover 

 of the plate was as well adapted to the one glass as the 



