31/53 Let ML be perpendicular to CL. And because I suppose the eyes R_r_ to be distant about a foot or so from the crystal, and consequently the angle RS_r_ very small, VB may be considered as equal to the semi-diameter CQ, and DP as equal to CL; then as N is to CQ so is CQ to DS. But N is valued at 156,962 parts, of which CM contains 100,000 and CQ 105,032. But CL is 99,324, being the sine of the complement of the angle MCL which is 6 degrees 40 minutes; CM being supposed as radius. |