BROAD-GUAGE OBJECTIVES, ETC. 233 



After experimenting 1 with the wide-angled inch, as 

 above related, we wrote to the Messrs. Spencers, asking 

 them if it w T as possible either to still further extend the 

 angle of the inch, or, maintaining the same aperture, 

 to increase its working distance. In reply, the elder 

 Spencer informed me that it would be difficult to fur- 

 ther increase the aperture or the working distance unless 

 the diameter ot the objective should also be enlarged. 



From this it would seem desirable to increase the di- 

 ameter of our low-power object-glasses, and this in turn 

 necessitates a change in the construction of the micro- 

 scope stand. Mr. Bullock's large stand, as also the Acme, 

 are especially arranged to accommodate these " broad- 

 gauge" low-power objectives. 



An one inch objective of large calibre is now in pro- 

 cess of construction for the author. The optician hopes 

 to endow it with an aperture of at least 62, maintain- 

 ing a working distance of one-eighth of an inch. 



It is but a simple act of justice to say that the idea 

 -conveyed to me by Mr. Spencer had already occurred to 

 Dr. W. W. Butterfield, of Indianapolis, Ind. While 

 in attendance at the congress of microscopists held in 

 Indianapolis in 1878, Dr. Butterfield showed me a 

 broad-gauge four-inch made to his order by London 

 opticians. He had also a stand then in process of con- 

 struction, and designed for the use of this class of ob- 

 ject-glasses. This, however, at the date mentioned, had 

 not arrived; consequently there were no accommoda- 

 tions for an examination of the objective. Should my 

 own glass be completed before these sheets go to press, 



