PKOCEEDINGS OP THE SOCIETY. 525 



Mr. J. Mayall, jun., described a somewhat remarkable instrument 

 from Mr. Crisp's collection, which he thought most persons would at 

 first sight be inclined to mistake for one of the old forms of reflecting 

 telescope, but which was really a Microscope, dating probably from the 

 commencement of the present century. It bore the name of Adams as 

 the inventor, and seemed to be a combination of an ordinary compound 

 Microscope and a projection Microscope, to be illuminated by a lamp, 

 or possibly by sunlight, though he scarcely inclined to the idea that this 

 was intended because the body had no movement in azimuth, but only 

 in altitude. The apparatus belonging to it was of an elaborate kind, 

 comprising various arrangements for carrying objectives of different 

 foci, also a spring stage and a very complicated stage on which opaque 

 objects could be viewed. There was a circular ground-glass screen for 

 receiving projection images, which fitted in a slot in the body-tube. 

 The instrument was evidently intended as a type of a first-class Micro- 

 scope of its day, both from the complexity of the design, and from the 

 care and finish bestowed on the workmanship. He had not yet been 

 able to meet with any description or figure of it. 



Mr. C. Curties exhibited two photomicrographs by Dr. Eoderick Zeiss, 

 of Jena, viz. : — 



Amphipleura pellucida x 2000 partly resolved into beads, taken with 

 an apochromatic 3 • mm. N.A. 1 ■ 40 oil-immersion objective. 



Pleurosigma angulatum x 4900 taken with an apochromatic 2 ■ mm. 

 N.A. 1*30 oil-immersion objective. 



Mr. J. Mayall, jun., considered these photomicrographs would bear 

 comparison with any they had yet seen. It would be remembered that 

 about a year ago they received some from Dr. Van Heurck, of Antwerp, 

 and Dr. Millar at the time called attention to the one of P. angulatum 

 in comparison with a transparent photograph by Nachet, of Paris, which 

 had been in the possession of the Society since 1867. In the case of 

 these now exhibited there was distinct progress shown ; in that of 

 Pleurosigma angulatum the features were beautifully defined and the 

 curious diffraction effects were well shown. The object itself was not 

 a difficult thing to photograph, but, with a power as high as that used 

 ( x 4900), to make a good picture was not an easy matter. The photo- 

 graph of Amphipleura pellucida showed the striations partly resolved 

 into beads, but in this case the resolution did not come out so clearly as 

 in the photograph by Dr. Van Heurck ; whether this beaded appearance 

 was real or whether it was the effect of improper illumination, as Mr. 

 Nelson alleged it to be, was a question which he must leave to others 

 to decide. During a visit to Antwerp, Dr. Van Heurck showed it to 

 him by means of the electric light ; therefore he had no doubt as to its 

 being seen. But it was worth mentioning that Dr. Zeiss used an 

 electric arc lamp in his experiments, and this method of illumination 

 was so unsteady — never two moments alike — and it altered the image so 

 frequently, that he doubted very much the possibility of getting the 

 finest effects by means of it. On the other hand, Dr. Zeiss had every 

 possible appliance at his command which could contribute to success. 

 He had concrete floors in his atelier, so as to ensure freedom from 

 vibration ; and he had also the pick of the fine lenses produced at his 

 works, so that if he could not produce good photographs, it was difficult 

 to say who could. 



