CHAP, i.] MIRRORS AND RKFLECTING INSTRUMENTS. 219 



as the surface changes through any cause. 1 Let us hope that this new 

 instrument, in the hands of skilful observers, will justify the expecta- 

 tions raised by the discoveries and astronomical researches which it 

 renders possible. 



1 The siderostat was made by M. Eichens, under the superintendence of MM. 

 Wolf and A. Martin. 



