ON THE MAGNITUDE OF THE SOLAR SYSTEM. Ill 



hitherto imagined? Probably the existing observations for the deter- 

 mination of most of these quantities are as exact as any that can ever 

 be made with our present instruments, and if they were freed from 

 constant errors they woukl certainly give results very near the truth. 

 To that end we have only to form a system of simultaneous equations 

 between all the observed (j[uantities and then deduce the most probable 

 values of these quantities by the method of least squares. Perhaps 

 some of you may think that the value so obtained for the solar parallax 

 would depend largely upon the relative weights assigned to the various 

 quantities, but such is not the case. With almost any possible system 

 of weights the solar parallax will come out very nearly 8.809" ± 0.0057", 

 whence we have for the mean distance between the earth and the sun 

 92,797,000 miles, with a probable error of only 59,700 miles; and for 

 the diameter of the solar system, measured to its outermost member, 

 the planet Neptune, 5,578,400,000 miles. 



