11 



37. Apparatus for examining crystals at a high tem- 

 perature. 



E. 84A. 1885. Made by E. Fuess, Berlin. 



Consists of a metal box, supported on two uprights with three 

 windows in the central part, one for the light from the signal to 

 enter and the other two for the telescopes. The box has a circular 

 perforation below to fix over the adjusting portion of the gonio- 

 meter ; its two ends are provided with hollow tubes of iron to be 

 heated in Bunsen burners, thereby heating the air within the box 

 and thus also the crystal, which is held by a pair of pincers in the 

 centre. The temperature is read off by two thermometers fixed 

 in perforations on the top. 



38. Wollaston's reflecting goniometer. 



B. 85. 1885. Made by E. Fuess, Berlin. 



In three separate parts fixed to a marble stand. One part is a 

 mirror turning about an axis ; opposite to this is the telescope, 

 sliding parallel to the same axis and provided with cross wires in 

 the eye-piece. The third is the silver graduated circle with 

 vernier and telescope, with the crystal holder rotating on the same 

 axis on an inner tube and provided with two screws at right 

 angles to the axis for adjustment. 



39. Wollasfcon's reflecting goniometer, belonging to and 

 used by the late Dr. Whewell, D.D., F.R.S., Master of 

 Trinity College, Cambridge, when Professor of Mineralogy. 



1876. Lent by Eev. Nicholas Brady, M.A. 



Early form, such as that described by Bauerman (Systematic 

 Mineralogy, p. 192), and in most treatises on Mineralogy. 



40. A simple substitute for a goniometer. 

 Contrived by the late Professor W. E. Miller, Cambridge. 



1876. 



The instrument consists of a long piece of wood with smooth 

 sides, to one end of which is screwed a vertical piece of brass 

 wire bent horizontal at the top and passing through a cork. 

 Through this cork is passed another horizontal brass wire at right 

 angles to the first, and its end is bent down vertically, and passes 

 into a third cork ; all these are movable about their axes, so that 

 a crystal fixed to the third cork can be turned about three axes 

 at right angles and made to take up any position. By means 

 of this a crystal can be measured by Wollaston's method, and the 

 angle of an edge determined by the determination of the angle 

 between two lines drawn on paper along the wooden part of the 

 instrument in its two different positions. 



