78 The President's Address. 



Passing from organized beings to apparatus, I find a 

 valuable paper, contributed by Dr. Carpenter in June, on 

 " Nacliet's Stereo-Pseudoscopic Binocular Microscope." 



From the construction of this instrument the observer is 

 able to pass immediately from a stereoscopic to a pseudoscopic 

 \ie-\v of any object under investigation. It is only necessary 

 to change the position of the prism figured in the illustra- 

 tions to this paper, in order to send the rays to the left eye 

 which belong to the right eye, and vice versa; the effect 

 being that all stereoscopic results are reversed. 



Dr. Carpenter also referred to the application of Nachet's 

 binocular magnifier to Beck's dissecting microscope, with 

 which he found its jjerformance of great value. 



Microscopic lamps have been brought several times before 

 us during the year. Mr. Lobb described and exhibited an 

 elegant little camphine lamp made by Young. Mr. Piper 

 exhibited a convenient and economical travelling lamp. 

 Messrs. Murray and Heath exhibited an ingenious telescope 

 lamp, made with sliding tubes, by which its height can be 

 varied; and Mr. Bockett exhibited a lamp (made by Mr. 

 Collins) furnished Avith a form of parabolic illuminator and 

 chimney screen, adapted to prevent the diffusion of light, 

 and to concentrate it in parallel rays proceeding in the direc- 

 tion required. 



Amongst the presents which have lately enriched the 

 Society's collection is a new four-inch objective contributed 

 by Mr. Ross. Low powers have been too much neglected 

 by modern microscopists. Messrs. Powell and Lealand in- 

 deed have been in the habit of making a dividing objective 

 of which the lowest power was four inches ; but its utility 

 does not seem to have been sufficiently perceived. Mr. Poss's 

 four-inch gives great satisfaction to those who have tried it. 

 It enables a satisfactory view to be obtained of many living 

 objects, such as polyzoa and compound polyps, too large for 

 higher powers. It also gives excellent results with many 

 anatomical preparations, entire insects, and large polariscopic 

 objects. When employed with the dcejier eye-piece and the 

 binocular microscope, it enables considerable magnification 

 to be obtained, accompanied by a depth of penetration Avhich 

 higher objectives with larger angles of aperture cannot give. 



Mr, Wray has presented to the Society a two-thii'ds objec- 

 tive with an angle of aperture of 50°. This glass is stated by 

 those who have examined it to possess a high degree of 

 merit ; but excessive angles of aperture are necessarily fatal 

 to penetration, and involve peculiar optical errors from a 

 confusion of perspectives. We very justly praise them as 



