430 On obtaining rapid Adjustments with Wollaston's Goniometer, 



eight hours, it is more probable that, unless some way be discovered 

 for taking into account the motions of the spots themselves with 

 reference to the mass, centuries will elapse before direct evidence 

 can be had either for or against the anticipated acceleration of 

 the sun's rotatory motion. 



LIII. On a Method of obtaining rapid Adjustments with Wol- 

 laston's Goniometer. By C. Greville Williams*. 



CHEMISTS who have been in the habit of using WoUaston's 

 goniometer are aware of the trouble and sometimes diffi- 

 culty of making each face of the crystal so reflect the black lines, 

 that, on moving the instrument until both approximate, they shall 

 be truly parallel, and at length, as the movement is continued, 

 perfectly coincide. 



Most operators find it difficult, in moving the crystal with the 

 fingers on the wax, to prevent disturbing the first adjustment 

 while making the second. With some crystals this is compara- 

 tively easy, with others great loss of time is occasioned by it. 

 The fact is, that the movements of the fingers are too coarse, and 

 it occurred to me that it would be extremely easy to make an 

 instrument that should possess one motion for one face of the 

 crystal, and a second for the other. -p- j^ 



Fig. 1 represents the contrivance I have 

 adopted before being attached to the gonio- 

 meter, fig. 2 shows it in its place. 



It will be seen that any chemist can con- 

 struct it with the tools to be found in every 

 laboratory. 



A small ring of brass is pierced with two grooves exactly 

 opposite each other, through which passes an axle supporting 

 in its centre a small ball, which in its turn has a hole drilled 

 through it, and tapped so that a vertical screw carrying two 

 milled heads can be inserted. One of these milled heads sup- 

 ports the crystal, the other serves to move it, and thereby com- 

 municate a horizontal motion. A lateral motion is obtained by 

 the horizontal axle, which enables it to be moved to the left or 

 right. The whole system is screwed into the small brass plate 

 usually used to support the crystal ; the entire arrangement is 

 seen in fig. 2. The pivot in fig. 1 is made to move stiffly by 

 means of two small plates screwed tight on to the grooves in 

 which it works ; moreover, from the vertical rod being formed 

 from a screw, it can be depressed so as to make the face of the 

 crystal lie exactly in the axis of the instrument. 



* Communicated by the Author. 



