PREFACE. XVli 



which we pass from the known elements to the phenomena; the former treat 

 of many most important problems which prepare the way to inverse pro 

 cesses. Since these very phenomena result from a certain artificial and intri 

 cate complication of the elements, the nature of this texture must be thor 

 oughly examined before we can undertake with hope of success to disentangle 

 the threads and to resolve the fabric into its constituent parts. Accordingly, 

 in the First Book, the means and appliances are provided, by means of which, 

 in the second, this difficult task is accomplished ; the chief part of the labor, 

 therefore, consists in this, that these means should be properly collected to 

 gether, should be suitably arranged, and directed to the proposed end. 



The more important problems are, for the most part, illustrated by appro 

 priate examples, taken, wherever it was possible, from actual observations. 

 In this way not only is the efficacy of the methods more fully established 

 and their use more clearly shown, but also, care, I hope, has been taken that 

 inexperienced computers should not be deterred from the study of these sub 

 jects, which undoubtedly constitute the richest and most attractive part of 

 theoretical astronomy. 



GOTTINGEN, March 28, 1809. 



