920 SEC. 18. BIOLOGY. 



3616a. Sorby's Standard Interference Scale, for 



measuring the position of absorption -bands in spectra. 



R. $ J. Beck. 



3616b. Sorby's Volute Diaphragm, for regulating the 

 amount of light for the spectrum microscope. R. <fy J. Beck. 



3617. Early Form of Machine, with Knife, for making 

 microscopical sections of wood, &c., devised by Andrew Pritchard, 

 F.R.S.E., prior to 1835. Dr. Urban Pritchard. 



The block of wood for section, if large enough, is fixed in the movable 

 triangular chamber by means of the little screw. The larger screw at the 

 bottom gradually elevates the whole, and the knife, held in both hands, shaves 

 off thin sections as the wood is raised. Should the piece of wood be too small 

 to be placed in the triangular chamber, it must be glued on, to a block of 

 convenient size. 



The whole machine is made to screw on to a bench. 



3613. Freezing Apparatus. A simple form for preparing 

 soft tissues for microscopical examination, consisting of a solid 

 copper cylinder with wooden handle and felt cap to fit over 

 cylinder. Dr. Urban Pritchard. 



Mode of use : Immerse cylinder in mixture of ice and salt for a few 

 minutes ; then remove and wipe, place tissue to be cut, after being moistened 

 with gum, on metallic end. Put felt cap over cylinder ; tissue will be frozen 

 and ready for cutting in two or three minutes. 



3614. Glass Microtome for microscopical sections o 

 hardened or frozen tissues. Dr. M. E. Mulder, Groningen. 



The hardened tissue, previously imbedded in a cylindrical mass of wax, 

 consisting of a mixture of Stearine - - 30 



[Hogs 'lard- - 24 



White wax - 16 



is introduced into the glass tube of the microtome, which is polished at 

 its upper margin. 



Any rotation or movement of the wax cylinder, which is exactly of the same 

 size as the tube, is prevented by the four pins. The wax cylinder can be 

 moved up or down by means of a screAv, and sections are made by passing a 

 knife over the polished surface of the tube. 



The thickness of the sections is indicated by the lines on the screw. (Every 

 line is -^ mm.) 



When the microtome is used for freezing, the glass tube is unscrewed and 

 replaced by the freezing box. The tissue, imbedded in a solution of gum 

 arabic, is frozen by filling the freezing-box with snow or ice and salt. 



3618. Apparatus for muintaining an even Temperature 

 in Microscopic Observations. 



Geneva Association for the Construction of Scientific In- 

 struments. 



This instrument is intended for performing microscopic operations in a 

 perfectly even temperature by means of hot water circulation. A small spirit 

 lamp is placed under the reservoir at the extremity of the apparatus. A 

 thermometer placed inside the instrument serves to regulate the temperature* 



