IV. DRAWINGS. 33 



These are specimens of a series of models designed for illustrating the 

 various propositions in descriptive geometry. They are especially designed 

 for lecturing purposes, for which their simple construction, and the capability 

 which they possess of folding into small compass, well adapts them. 



166. Stereoscopic Figures, for demonstration and use in 

 the study of stereometry and spherical trigonometry. Edited 

 by Julius Schlotke. L. Friederichsen and Co., Hamburg. 



167. The principal Problems of Descriptive Geo- 

 metry, represented by stereoscopic figures, by Julius Schlotke. 



L. Friederichsen and Co., Hamburg. 



168. Stereoscopic representation of a number of the most 

 important crystals, their combinations, &c., by Julius Schlotke. 



L. Friederichsen and Co., Hamburg. 



The stereoscopic figures of Schlotke are as yet the only ones of their kind 

 in use for illustrating instruction in descriptive geometry and crystallography, 

 in polytechnic and other higher educational institutions, where they are much 

 appreciated. 



More particularly the division of crystallography is recommended, as it 

 renders unnecessary the usual expensive models, and, better than those 

 models, demonstrates the combinations and growth of crystals. 



A stereoscopic apparatus is placed near the objects. 



39508, 



