76 On a Self-acting 



a positive significance in the formation of mineral deposits. 

 In a reef near Wellington, New South Wales, I discovered 

 quartz traversed by thin veins of agalte, and with fortifica- 

 tion agate in small geodes in the mass. Inside one of these 

 geodes was a lining of quartz crystals, and concerning this, 

 to my mind, remarkable example, I think you will admit 

 that there is something very interesting to be unriddled in 

 those natural changes which can fill the crevices and in part 

 the cavities of a massive quartz reef with colloidal silica, 

 and afterwards fill up the interior of the colloidal deposit 

 with crystals of quartz. 



EXPLANATION OF ACCOMPANYING PLATES. 



FIRST PLATE. 



1. Annular residue, from evaporation of a drop of water from interior of 



enhydros ; real size. 

 2 and 3. Microscopic view of portions of the margin of this residue. 

 4. Examples of crystalline foims, obtained by recrystallizing the residue 



obtained from iifteen drops of water from enhydros. 

 6. Residue of silicic acid, patches left ou the glass capsule, as though a 



pellicle of colloidal silica bad dried up. This residue is insoluble, or 



nearly so, in distilled water. 



6. The same film broken up, and floa'ing in shreds in water added to it. 



7. Impress of crystals in this coloured colloidal residue. 



The parallel ruled lines, in figures 6 and 7, represent a pale ochreous 

 tint in the original drawing. 



The second plate shows crystalline structure of laminte forming walls of 

 the enhydros. 



Art. XXIII. — On a Self-Acting Hydrostatic Chime and 

 Clock Weight By Alex. K. Smith, G.E., F.R.S. S.A. 



[Read 8th May, 1871.] 



A considerable amount of time and labour, and conse- 

 quently expense, is required under the system at present 

 in use, to wind up the heavy driving weights of large 

 clocks, chimes, &c. ; the expense being further increased 

 by the necessity of making special preparation for a long 

 descent of the driving-weights in the tower or building 

 where the' clock or chimes are situated ; -and as the 

 weights are in most instances very heavy there is more 

 or less danger attending their use. 



During the time that clocks and chimes for the New 

 Post Office and Town Hall were under consideration, I 

 thought over the subject at some length, with the view of 

 altogether dispensing with the laborious process of winding 

 up the heavy driving-weights generally used, and for that 

 special purpose designed the plan I now submit to you. 



Whilst the Post Office clock was being constructed under 



