CONTRIBUTIONS TO MICRO-MINERALOGY. 281 



to try it, and it answered its purpose admirably ; thus two 

 persons were working out the same principle at the same 

 moment (as has frequently happened before in the records of 

 Science) quite independently of each other ; and I think Dr. 

 Leeson* can as fairly claim this form of Microscope for 

 England as Professor J. L. Smith may for America. 



The principle of introducing- reflecting prisms into the 

 construction of the Microscope was, I believe, first employed 

 by Chevalier of Paris, who used a triangular prism in the 

 body, over his lenses, these being attached at right angles to 

 the body and pointed down to tlie stage ; here, however, the 

 prism was a more tlian useless intervention, the prism only 

 being justified (on account of loss of a small portion of light) 

 when the object-glass is to be placed under the object, as in 

 cases where vapours would arise, and thus dim or attack 

 lenses placed over them ; this specially obtains when chemical 

 solutions are to be examined, and where heat must be em- 

 ployed. If, however. Chevalier, by a modification of his 

 arrangement, used, as I believe he did (though I have never 

 seen his instrument), the lenses under the object, then the 

 PRINCIPLE is due to him ; the advantageous modification of the 

 angle at which the body is placed, and the resulting position 

 of the stage, to Professor Smith and Dr. Leeson ; the econo- 

 mical adaptation of Soleil's and other instruments, and the 

 general improvement in the arrangement and adjustments to 

 myself. 



In the beginning of 1851 1 sent a coloured drawing of the 

 instrument as I required it modified, and as represented in 

 fig. 3, to M. Nachet, who, however, from press of business, 

 could not get it made for me as quickly as I wanted, and I 

 afterwards got it executed in this country ; Kobell's Stauro- 

 scope I have, of course, added since. 



The instrument Professor Smith calls the Inverted Mi- 

 croscope, I, in its modified form and from its more general 

 application to crystallologic al researches, call the Minera- 

 LOGiCAL Microscope, which I shall now proceed to describe. 



The instrument is shown in fig. 3, as arranged for ordinary 

 structural observations, whilst in fig. 4 it is represented in 

 section, arranged for the optical characters of mineral bodies. 



The Ba*c — on a Central pivot, screwed into a solid circular 

 base, rotates a plate that carries the body, prism-box P, object- 

 glass and fine adjustment A ; to the side of the base is firmly 

 attached a square bar G, that carries the principal stage with 



* Dr. Lecsou has never described this, or laid any claim to the iuvcn- 

 Lioii as yet. 



