136 



ROGERS AND McLEOD ON THE 



6 = a constant due to the unsteadiness of the stellar image arising from atmospheric dis- 

 turbances. It is the same for all telescopes and is greatest near the horizon. 



c ^ a constant dependent upon the sense of sight, and which varies therefore with the 

 magnifying power. 



n = the magnifying power of the telescope with which the constant c, considered as a 

 standard of reference, has been determined. 



m = the magnifying power of the telescope used. 



q the parallactic angle. 



"Wagner (" Observations de Poulkowa," Vol. L, p. 85) has giA'cu for the maguiiying 



power of 206. the equation 



w= /(0'.067) + (0%016)-sec- rt\ 



And the general equation 



— y (0^06-)- + \-~^^ (0^01(î)■^ sec- d\ 



In the '■ Coast Survey Report for 1880," p. 3G, there is given a determination of the 

 relative weights which attach to the particular class of instruments described. The 

 following useful table is transcribed from this volume. 



Relative "Weights. 



