Megadiascope. 



1211 



of the rotating and centrable vulcanite stage, the stand is also supplied with cross stage or microphoto- 

 graphic stage. The prices are given in the second part of this catalogue. 



The microscope stand is mounted on a special slider with fixing bridge (F i g. 9) which is fixed 

 o the optical bench by means of a turnbuckle. Fillets on the slider maintain the stand in the correct 

 position. The bridge and a nut hold the foot of the stand firmly on the slider so that the stand cannot 

 fall through. 



In many cases preparations are used with the object glass in a horizontal position, and the 

 microscope must therefore assume a vertical position. In such cases a special arrangement is employed 

 for placing the microscope stand higher on the optical bench (F i g. 10). A special mirror is then 

 necessary for the purpose of illuminating the object; also an erecting mirror, placed on the tube of 

 the microscope, and a rectifying prism: the latter being essential when it is desired to work with oculars. 



The optical outfit which we recommend is that catalogued as "Complete Optical Outfit" in this 

 list. We shall be pleased, however, to quote for simpler outfits. 



All disturbing light is held off by a curtain fitted on to a drop board. 



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7. Projection of Stable. Flowing and Liquid Crystals (Fig. 11). 



For demonstrating crystallisation (an important and interesting section of physics and physical 

 chemistry) a special Projection Microscope is requisite which permits of the preparation remaining 

 in a horizontal position and renders it possible to heat and cool the preparations 

 as desired, and which can be fitted with electric leads for electrolytic experiments. 

 An arrangement has been provided whereby a polariser and analyser can be 

 rapidly interposed in the passage of the rays: it is thus possible to show the peculiar 

 structure of the liquid crystals, which cannot be demonstrated in ordinary light. 



With this object we have constructed a Projection Microscope based on the 

 suggestions of Prof. O. Lehmann (Karlsruhe), the discoverer of liquid crystals, 

 and we supply all the necessary accessories as well as chemicals, preparations, col- 

 lections of preparations: also diapositives from photographs which have been 

 taken during the process of crystallisation, and especially of the phenomena of 

 liquid crystals, which have been closely studied by Prof. Lehmann. These 

 phenomena have shown that considerable analogies exist between the liquid 

 crystals and many of the lower animalculae. Prof. Lehmann observed, for in- 

 stance, that certain of the liquid crystals as it were devour each other; others 

 grow together and form a large subject of similar shape; in the case of some of 

 the crystals buds form in the liquid state, and new independent shoots grow from 

 these buds. Many needle shaped crystals distribute themselves like bascillae in 

 a number of smaller needles, which continue to grow and finally themselves acquire 

 the property of distributing themselves. There are liquid crystals having the 

 shape of snakes and earth worms, which as it were endowed with life move back- 

 wards and forwards, turn themselves about their vertical axis or execute ser- 

 pentine movements. With the aid of this apparatus it is possible to demonstrate 

 before the very eyes of the audience the fact that regular shaped crystals which 

 have lost their complete form 'on account, say, of mechanical influences have 

 their broken ends restored -- their injuries, so to speak, healed. In addition, the 

 crossing of various kinds of crystals, the existence of mixed crystals, the prevention 

 of the growth of the crystals in solutions to which foreign bodies are added, that 

 is to say, a kind of poisoning can readily be observed by the intermediary of the 

 apparatus stated. We might make mention here of the following publications by Prof. Lehmann 

 dealing with the subject: ..Fliissige Kristalle'', Leipzig 1904; ,,Fliissige Kristalle und die Theorien des 

 Lebens". Leipzig 1906; ,,Die scheinbar lebenden Kristalle, Anleitung zur Demonstration". Esslingen 

 I'.tuT: Frick-Lehmann ,,Physikalische Technik", Vol. I, Part 2, and Vol. II, Part 1, Brunswick 1905 

 and 1007 respectively. 



We shall be pleased to send a complete descriptive list, with prices, on application. 



Fig. 11. 1 :9. 



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