452 Notices respecting New Books. 



The crystal showed, resembling in that also a magnetic 

 needle, strong polarity; the same end being always directed 

 to the north. I think this may be b. polarity of the opto-mag- 

 netic 2)ower. Two questions too may easily be answered : — 

 1st. Is the north pole indicated by the forms of crystalliza- 

 tion ? 2nd. Did the crystal obtain, when formed, its polarity 

 by the magnetism of the earth ? Between the poles of the 

 strong electro-magnet the permanent polarity disappeared as 

 long as the magnetism was excited. 



I am obliged, by the new facts mentioned above, to take up 

 my former memoir ; I must reproduce it under a quite new 

 shape. I will examine again the rock-crystal, which, being 

 acted upon weakly by a magnet, induced me to deny in that 

 memoir, what I ascertain now and what I thought most pro- 

 bable, as soon as I received the first notice of your recent re- 

 Searches. [That you will find in the memoir given to M. Pog- 

 gendorff two or three months ago.] Perhaps the exceptional 

 molecular condition of rock-crystal, as indicated by the passage 

 of light through it, will produce a particular magnetic action. 



I should be very much obliged to you, if you would give notice 

 of the contents of my present letter to M. De la Rive, when he 

 calls on you, as he intended to do. I showed him several of 

 my experiments when he passed through Bonn the 12th of 

 May. The following day I obtained the different results men- 

 tioned above. 



My best wishes for your health. 



Very truly yours, 



Plucker. 

 Bonn, the 20th of May 1849. 



LXVIII. Notices respecting New Books. 



Outlines of Astronomy. By Sir John F. W. Herschel, Bart., K.H., 

 8(C. 8vo. London : Longman and Co., 1849. 



THE treatise on Astronomy by Sir John Herschel, published in 

 1833 as a Part of the Cabinet Cyclopaedia, is familiar to every 

 student of that science, and justly prized as containing one of the 

 most lucid and eloquent expositions of its facts and principles ever 

 given to the world. A new edition of this popular and standard 

 "work, brought down to the present day, had become necessary by 

 the progress of discovery. In the course of the sixteen years which 

 have elapsed since the original publication, astronomy in all its 

 branches has been assiduously and successfully cultivated. Six new 

 planets have been added to the solar system (and w^hile we write 

 a seventh is announced) ; a satellite to Saturn, and one or two to 

 the recently discovered large planet ; a multitude of comets have 



