ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1061 



These prisms are adjustable so that the image may be viewed at any 



inclination between the vertical and the horizontal. The combination 



of the binocular prisms with the eye-piece 



prisms inverts the image in both planes, 



so that the movement ujjon the stage is 



seen through the instrument to be natural 



or erect — " a condition essential to the 



convenient manipulation or dissection of a 



microscopic object." 



In the original description Professor 

 Eiddell states that the instrument, with 

 its firm stand, broad stage [6 by 4 in.], 

 and erect images, is pre-eminently adapted 

 for use in prosecuting minute dissections, 

 or the unravelling of minute structures 

 of any kind. Opaque objects may be 

 illuminated by the buH's-eye condenser, 

 and transparent objects by one or two 

 concave mirrors, aided perhajis by two 

 diaphragms or screens. At night two 

 candles may be used conveniently with 

 one mirror. To illuminate lor the higher powers a single achromatic 

 condenser suffices. 



Megaloscopy.* — Under this heading M. Boisseau du Rocher writes 

 as follows : — 



" I will first indicate the optical principle that has guided me in 

 the construction of a series of instruments for the inspection of cavities, 

 notably the stomach, bladder, and rectum (/xe'yas, large, ct/cwi', image, 

 crKOTrciv, to see^. 



The problem was to pass through a tube 7 mm. in diameter and 

 50 cm. long, the image of a very near object of the dimensions of 

 20 cm. To accomplish this I reduced the image of the object to 

 microscopical dimensions by means of a suitably placed objective. 

 This image, visible in the lower part of the instrument, is then 

 examined with a telescope, which I call a megaloscopic telescope. 

 It will be understood that with lenses of suitable focal length the 

 reduced image of the object can be magnified, and consequently 

 observed with the normal dimensions of the object. 



The application of the principle is as follows : — The instrument is 

 in the form of a tube or probe, terminated at its extreme end by a 

 lantern in which is fixed an incandescent lamp. Above it is the 

 optical arrangement which reduces to microscopical dimensions the 

 image of the mucous membrane to be observed. This is composed 

 of a right-angle prism ; above arc two plano-convex lenses with their 

 convex surfaces facing each other, whicli have given the best results, 

 whether in regard to the diminution of the image and of the field of 

 view, or to distortion wliich is thus absent. At the other end of the 



• Comptes Rendns, ci. (188:)) pp. .']2f>-,30. 

 8er. 2.— Vol. V. 



3 Z 



