t^ 



AN ESSAY 



on THE 



PRESENT STATE OF ASTRONOMICAL CERTAINTY, 



WITH REGARD TO THE 6UANTITY OF THE EARTH'S MAGNITUDE, THK DISTANOE OF 



THAT PLANET FROM THE SUN, AND THE ABSOLUTE LIMIT OF THE 



SMALLEST POSSIBLE INTERVAL FROM THE SUN TO 



ANV ONE OF THE FDCED STAKS. 



By the Kev. J. A. HAMILTON, D. D. DEAN of CLOYNE. 



.s^Q^O^^^ 



Observatory, Armagh. 



To ascertain the dimensions and distances from each other, 

 of the various bodies that compose our solar system, is a pro- 

 blem Avhich, we find, has exercised the ingenuity of Astrono- 

 mers, from the period of the earhest records we have, of the 

 application of trigonometrical calculations to the improve- 

 ment of their useful and sublime science. To determine the 

 various questions involved in this enquiry, an actual know- 

 ledge of the distance of the earth from the sun, is first re- 

 quired; an element of great importance in this, and, indeed, 

 in many other branches of astronomical calculation. As the 

 works of Ptolemy make no mention of any Chaldean or In- 

 dian attempts at the solution of this problem, it is probable 

 that none such existed in his time, as there can be no doubt, 



that 



