88] Microscopic Illustrations^ 



to put a fly's eye before the object-glass, and a fool's eye before 

 the eye-piece ; with many other things equally curious, important, 

 and interesting j and if perchance, I shall succeed in teaching 

 thee how to deal with the instrument under consideration, toge- 

 ther with the Amician reflector, the management oi all others thou 

 canst meet with will be as easy to thee, as the guidance of a cock- 

 boat to the seaman who can work a line-of-battle ship." — p. 61. 



** Courteous reader, I have endeavoured to supply the place of 

 a viva voce lecture on the instrument, and to infuse into thee 

 such knowledge as I possess, touching the management of the 

 aplanatic engiscope, &c. I hope it will be found sufficient for 

 ordinary objects ; but under the head of Test Objects, I shall enter, 

 into the subject still more minutely, and give still more precise 

 and specific instructions, as the case may seem to require. I 

 cannot help thinking, however, that the directions already given 

 will be found much more explicit, clear, and intelligible, as well 

 as more full, particular, and diffuse, than any others hitherto 

 given in print. Valeant quantum valere possimt. By their as- 

 sistance, thou shaltbe enabled to enter into a course of researches, 

 very nearly as profitable to thyself and fellow-creatures, as if thou 

 Avert engaged in the sublime and important occupation of deter- 

 mining whether the small star of e Bootis is of a greenish-blue, 

 or bluish-green, or whether some nebula is very gradually, or 

 very suddenly, much brighter in the middle." — p. 90. 



On Thorina. By Professor Berzelius. 



[Continued from p. 302 of last Volume..] 

 2. EXAMINATION OF THORINA AND ITS METALLIC RADICAL. 



Thorina is reduced neither by carbon nor by potassium ; but 

 thorium can be isolated either when the double fluoride of 

 horium and potassium, or when anhydrous chloride of thorium 

 s mixed with potassium and heated. The latter mode succeeds 

 best, and gives the purest thorium. Chloride of thorium is 

 prepared from thorina, by mixing with carbon, and heating to 

 redneijs in a stream of chlorine gas. The decomposition of 

 the chloride of thorium takes place with a very slight detona- 

 tion, accompanied, if the chloride of thorium be altogether free 

 from water, only by the development of heat without light, 

 and it can be safely enough performed in glass. Even the 

 fluoride produces with potassium a very slight detonation. 



To satisfy myself that thorina is not reduced by potassium, 

 I mixed anhydrous sulphate of thorina with potassium in 

 slight excess, and heated the mixture in a covered porcelain 

 crucible. The decomposition took place, with an exceedingly 



