HIS IMPROVEMENTS IN THE TELESCOPE. 271 
of each of the illustrious observer’s memoirs, containing 
‘a detailed indication of the improvements or corrections 
that 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 7reatise 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 
due to him. 
IMPROVEMENTS IN THE MEANS OF OBSERVATION. - 
The improvements that Herschel made in the construe- 
tion and management of telescopes have contributed so 
directly to the discoveries with which that observer en- 
riched 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, 
