Xra i.TirKOVEMENTS INT THE TELESCOPE. 271 



of each of the illustrious observer's memoirs, containing 

 a detailed indication of the improvements or corrections 

 tluit the progressive march of science has brought on. 

 But in order to avoid an exorbitant length in this biog- 

 raphy, I have been obliged to give up my project. In 

 general I shall content myself with pointing out what 

 belongs to Herschel, referring to my Treatise on Popular 

 Astronomy for the historical details. The life of Her- 

 schel had the rare advantage of forming an epoch in an 

 extensive branch of astronomy; it would require us 

 almost to write a special treatise on astronomy, to show 

 thoroughly the importance of all the researches that are 

 e to him. 



IMPROVEMENTS IN THE MEANS OF OBSERVATION. 



The improvements that Herschel made in the construc- 

 and management of telescopes have contributed so 

 ly to the discoveries with which that observer en- 



jhed astronomy, that we cannot hesitate to bring them 

 forward at once. 



I read the following passage in a Memoir by Lalande, 

 printed in 1783, and forming part of the preface to vol. 

 viii. of the Ephemerides of the Celestial Motions. 



" Each time that Herschel undertakes to polish a 

 mirror (of a telescope), he condemns himself to ten, or 

 twelve, or even fourteen hours' constant work. He does 

 not quit his workshop for a minute, not even to eat, but 

 receives from the hands of his sister that nourishment 

 without which one could not undergo such prolonged 

 fatigue. Nothing in the world would induce Herschel 

 to abandon his work ; for, according to him, it would be 

 to spoil it." 



The advantages that Herschel found in 1783, 1784, 



