172 THE MICROSCOPE. [August, 



or illuminators with heliostats, lime-lights or electric lanterns, 

 well adapted to this work. 



Photomicrographs in great number and variety and of every 

 degree of excellence were displayed upon the walls and crowded 

 in the cases not only of the main hall but also in a separate room 

 devoted to them. 



Thirteen prizes, of several different grades, were awarded in 

 this department. The first of these would certainly have been 

 voted to Dr. Van Heurck for his photographs of diatoms, on 

 account of the clearness and general excellence attained in treat- 

 ing subjects chosen for their extreme difficulty ; but, though not a 

 member of the jury of awards, his prominent connection with the 

 enterprise as the originator of the exposition and the leader of its 

 management led him, with very good taste, to decline to be 

 considered a competitor for any prize. 



One grand prize was awarded, to Dr. Giorgio Roster of 

 Florence, who exhibited four dozen extremely fine photographs 

 of natural-history objects, including diatoms, and of pathological 

 subjects. These were models of good photography and mount- 

 ing and of scholarly labelling and arrangement. 



Four diplomas of honor followed : one to Prof. J. D. Cox of 

 Cincinnati and Mr. C. Houghton Gill of England, who conjointly 

 with Dr. Van Heurck exhibited a number of diatom photographs, 

 magnified from 500 to 1,500 times, displaying the structure of the 

 shells in a decisive manner by means of edge views of broken 

 fragments of valves with their areola filled in with silver 

 sulphide, mercurous sulphide, or platinum ; one to Mr. 

 Andrew Pringle, and one to Mr. Thomas Comber, both 

 of England, for fine diatom photographs ; and one to F. Thevoz 

 & Co., of Geneva, for a large and excellent variety of " photo- 

 types." impressions suitable for book illustrations, from photo- 

 rnicrographs of diatoms, infusoria, microbes, and natural-history 

 objects generally. 



A novel and remarkable series of photomicrographic transparen- 

 cies suitable for the magic lantern was shown by Antoine Lumiere 

 & Son, of Lyons, France. The gelatin bromide of silver trans-* 

 parencies were cleared and stained, by some process claimed as 

 original, so that the color of the object as seen in the field of the 

 microscope was exactly reproduced. Thus desmids, for instance, 

 were stained a natural green, while microbes, animal tissues, or 

 plant sections, which are usually stained for the microscope, were 

 colored to correspond. The transparencies when lield up to the 

 light, or displayed by hanging in the w^indows. represented vividly 

 tlie field of view in the microscope itself, and in the magic lantern 

 or with a sufficiently low power of the projection microscope 

 they produced that effect well upon the wall. At a lecture in the 

 amphitheatre many of these views, including a series representing 



