Final Remarks on Immersion Ajyertures. 



125 



angles (E) which the ray, before crossing, makes with the axis, 

 numbered in the same order. 



Through the kindness of Dr. Woodward I am enabled to send, 

 to the care of the Editor,* several photograj^hic copies of the whole 

 computation for the inspection and review of those having sufficient 

 interest in the matter. 



[* Any gentleman who is desirous of possessing one of these 

 may do so on communicating with the Editor. — Ed. ' M, M. J. 'J 



Georgetown, D.C., July 9, 1874. 



III. — Final BemarJcs on Immersion Apertures. 



By J. J. Woodward, Assistant- Surgeon U. S. Army. 



In his reply to my article " On Immersion Objectives of greater 

 Aperture than corresponds to the Maximum possible for Dry Objec- 

 tives," t Mr. Wenham asks me : '• Can he show us the passage of the 

 rays through one of the object-glasses such as he advocates in a 

 diagram of correctly enlarged dimensions ? I shall then have 

 tangible material before me, and will enter upon the consideration 

 with enthusiasm." t To this demand I rephed : "If Mr. Tolles 

 thinks proper to deviate from the ordinary practice of those who 

 make objectives for sale, and to communicate for pubhcation the 

 details of the construction of either or both the objectives described 

 in my November paper, it will be an easy matter for me to gratify 

 Mr. Wenham, and I will endeavour to do so. Not that I think 

 this additional testimony needed to show the accuracy of my mea- 

 surements of the immersed apertures of these objectives, but because, 

 besides the value of the information to objective makers, I should 

 be hapj)y to be the means of adding to the scanty store of facts 

 which the objective makers have placed at the disposal of science." 

 The paper in which I made these remarks § having been communi- 

 cated to Mr. Tolles before its publication in England, he generously 



t This Journal, November, 1873, p. 210. 



X Ibid., December, 1873, p. 257. • 



§ Ibid.. Mi.rch, 1874, p. 121. 



