1894.] MICROSCOPICAL JOURNAL. 185 



2. The substage is suspended on a pivot to swing out of the 

 optical axis when not in use. 



3. The tail piece swings forward, and the mirror being at- 

 tached by a saddle and crank arm, can be adjusted for use 

 above the stage. 



Increasing Angular Aperture. — The owners of high angle 

 objectives are indebted to Dr. Henry G. Piflard of New York, 

 for valuable hints as to the use to which such lenses can be put, 

 in which the angular aperture can be considerably increased. 



He found that a I inch water immersion having an angular 

 aperture of 143°, would also work perfectly well with cedar oil, 

 and more recently he discovered that by closing the svstems as 

 far as the correction collar would permit, and shortening the 

 tube length to about 155 mm. that the objective would correct 

 perfectly with mono-bromide of naphthalin. By these means 

 he increases the aperture to N. A. 1.56. 



Dr. Pitiiird made several experiments with other lenses on 

 this basis, and found that most of them but not all, would re- 

 spond to this tieatment. In order to obtain the benefit of the 

 full aperture here described, it is necessary to have at command 

 adequate substage illumination, and of course the objective 

 must have the collar adjustment. 



I have a dry 1-6 inch of 165°, and have made a few experi- 

 ments with it, following Dr. Piffard's suggestion and find it can 

 be used as a very good water immersion lens. Dr. Piffard con- 

 cludes by making a suggestion as to what an ideal immersion 

 lens should be for general bacteriological, biological and histo- 

 logical work. Thus, it should have the largest practical angu- 

 lar aperture and be corrected for either the 160 mm. or 216 mm. 

 tube, and a cover-glass not exceeding .20 mm. The adjustment 

 should be arranged to close a little beyond the mono-bromide 

 point, and open a little beyond the oil point, so as to permit 

 the objective to be used at will for either fluid. 



John Michels. 



A Cheap Instrument. — T. S. Middleton has made a mi- 

 croscope for $5.45 Avhich he says any one can dui)licate. 



Take a board two feet long, four inches wide, one inch thick. 

 On its edges screw paralled strips having beveled edges. In this 

 slot, the various parts slide during adjustment. The tunnel is 



