I. MICROSCOPES. 921 



3619. Camera for Microscope. 



Geneva Association for the Construction of Scientific In- 

 struments. 



3620. Two B.OSS Compressors, for the Microscope. 



(Ordinary models.) 



Geneva Association for the Construction of Scientific In- 

 struments. 



3621. Compressor, by Schick, for the Microscope. 



(Ordinary model.) 



Geneva Association for the Construction of Scientific In- 

 struments. 



3622. Microtome, with inclined plane for producing micro- 

 scopic sections of extreme tenuity and regularity. 



Geneva Association for the Construction of Scientific In' 

 strumcnts. 



3623. Microtome by Professor Wilhelm His. 



Geneva Association for the Construction of Scientific In- 

 struments. 



Many instruments for making microscopic sections exist, but most of them 

 have been distrusted by scientific men. This distrust was more or less justified 

 by the imperfection of the apparatus known hitherto, and it was mostly pre- 

 ferred to operate simply by hand, without its being possible to calculate with 

 positive accuracy the thickness of the section. 



During the course of his studies upon vertebrated animals, Professor W. 

 His, of Basle, found the absolute need of an instrument for rapidly effecting 

 sections of positive uniformity in thickness. 



It is from his suggestions that the Geneva Association for the Construction 

 of Scientific Instruments has constructed a Microtome, which has now the 

 complete approbation of the scientific men who have had occasion to use it. 



The requirements were : 1, that the knife should be directed very securely 

 while remaining independent of the apparatus ; 2, that the object to be 

 sliced should be movable in a parallel line under the knife, and that the amount 

 of the displacement should be read with great accuracy ; 3, that the object 

 should be fixed firmly in any position. 



The instrument consists of a table, 75 mm lorg and 60 mm wide, capable of 

 being inclined at will upon its foot. The table has a small tongue which is 

 movable in parallel line by means of a micrometric screw indicating 1 ^- ths 

 of a millimetre. To the tongue is affixed a stay, having a tightening screw, 

 under which is placed the object to be sliced. Above the table is a kind of 

 steel arch bearing a plane, perfectly adjusted, perpendicular to the table. It 

 is upon this surface that the knife, of which one side is also adjusted with the 

 greatest care, is made to slide by hand. 



3624. Professor Vogelsang's Apparatus, serving to raise 

 the temperature of Microscopic Objects. 



From the Collections of the Royal Polytechnic School at 

 Delft, Prof. J. Bosscha. 



By this instrument it was shown that the air bubble in the liquid carbonic 

 acid contained in quartz crystals ceased to be visible at a temperature of 

 about 32 C. (Poggendorffs Annalen, vol. 137, table III., fig. 2.) 



