30 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



from which is read off the area of any figure whose outHne 

 has been followed by the tracer of the instrument. When 

 the cone was employed as a multiplier it was easy to fix 

 upon the proper proportions, so that the number of revolutions 

 of the index-wheel in relation to those of the moving wheels 

 and of the cone, being always directly in proportion to its 

 distance from the apex of the cone, the area of the figure 

 would be indicated. No Planimeter, however, had been in- 

 vented in which the errors arising in using the instrument had 

 been entirely got rid of, such as the retardation of the index- 

 wheel by the compound sliding and revolving motion in the 

 back-action. 



FOURTH MEETING. 



Fourth Meeting, 27th November, 1886, the President in 

 the Chair. 



Exchanges since last meeting, 45. 



F. Chamberlain, B.A., and George Andrew McKinnon, 

 were elected members. 



F. T. Shutt, M.A., F.C.S., read the following paper on 



CANADIAN APATITE. 



Amongst the economic minerals that enrich the Dominion of 

 Canada, Apatite (commonly known as "Phosphate") holds a promi- 

 nent position. 



The vast deposits of this valuable mineral, which occur in various 

 parts of Canada, are now, and liave been during the last fifteen years, 

 extensively worked, until now phosphate mining is recognized as 

 standing in the front rank of our mining industries. The annual 

 " out-put" steadily increases, for while in 1875 only 3,701 tons were 

 exported, in 1884 nearly 25,000 tons were mined. These figures 

 go to show that this industi-y is fast becoming one of great commei'- 

 cial importance, and, considering the value of " Superphosphate " as 

 a fertilizer, one which demands the highest scientific treatment. 



The name "Apatite," derived from the Gi^eek verb anarduj, I 

 deceive, was first given from the great similarity which this mineral 



