132 NEW OBJECTIVE. 



among the fixed stars is eastward till the end of May, when it 

 begins to retrograde. 



Satuini is very near Reguhis, the bright star in Leo. It 

 recedes very slowly westward from that star until the 29th of 

 April, when the distance will be about 2 degrees ; it then 

 approaches and overtakes the star on May 30, and, passing it, 

 continues its course eastward. 



An Italian astronomer, Schiaparelli, has been carefully observ- 

 ing the markings on the disc of the planet Mei'cury^ and has come 

 to the conclusion that the planet rotates on its axis in the same 

 time that it revolves round the sun. If this be the case, we 

 have the singular arrangement of a planet with a great part of one 

 hemisphere in total darkness, and a great part of the other 

 exposed to perpetual sunshine. It is to be hoped that with some 

 of the large telescopes now in use this remarkable conclusion will 

 be tested. 



mew ©bjcctivc of 1-63 m.H. 



THOSE of our readers who may have become possessed of 

 one of the recent Apochromatic Objectives of 1*4 N.A., 

 will be interested in hearing of a lens of still wider aperture. 

 This new objective of i"63 N.A. has been constructed accor- 

 ding to the formulae of Professor Abbe, in the optical 

 factory of Carl Zeiss. The immersion is not really homo- 

 geneous, but is of monobromide of naphthaline, whose index is 

 I '65, the front lens of flint glass (index 1.72), while the cover- 

 glass, into which the preparation has to be melted, is of the same 

 material. The condenser must, of course, as indeed should be 

 the case with all objectives, be of the same aperture. The covers 

 have to be ground down to the required fineness, and carefully 

 polished ; hence they are very costly. So far, diatom valves have 

 been found the most suitable objects for such a method of 

 mounting, owing to their practical indestructibility. The only 

 difficulty in the way of increasing even this wide aperture, lies in 



