jg26.1 Analyses of Books. 281 



sliffht decomposition by the action of hydrosulphuric acid, as 

 may be easily imagined ; but, what is not so obvious, is, that 

 the carbonates, according to the same observer, are rnore diffi- 

 cultly decomposed by hydrosulphuric acid than the hydrosul- 

 phates by carbonic acid. 



Article XI. 



Analyses of Books. 



1 Philosophical Transactions of the Royal Society of London, for 



1825. Part IL 



{Conclude.d fro}mp. 223.) 



In the next number of the Annals, we shall give a general 

 account of the present state of science, on the subject ot the 

 magnetism developed in various substances by rotation, embrac- 

 ino- the principal contents of the four papers on that subject 

 contained in this part of the Philosophical Transactions. 

 Articles XIV. and XVI. therefore, being the papers on the mag- 

 netism of iron arising from its rotation, by Messrs. Barlow and 

 Christie, we shall at present pass over; and Art. XV. is the 

 paper by Sir H. Davy, which we have inserted in the present 



"^XVn Some Account of the Transit Instrument made by AB: 

 .Dollond, and lately put up at the Cambridge Observatory. By 

 Robert Woodhouse, Esq. AM. FRS. 



The dimensions of this instrument are nearly the same as those 

 of the Greenwich transit made by Mr. Troughton. 



Ft. In. 



Its focal length is 9 10 



Its aperture ^ ^ 



The lensth of the axis between the piers 3 b 



The weight of the instrument is 200 pounds. It was counter- 

 poised • but after repeated trials, Mr. Woodhouse has been 

 oblic^ed to abandon the counterpoises for the present, for 

 instead of relieving the instrument, they rendered it unsteady. 

 The whole leno-ths (two inches) of the pivots rest on the Is. 

 Seven fixed wires are placed in the focus of the object glass, 

 and two other wires moveable by a micrometer screw; the 

 interval of which wires is equal to the interval between any two 

 •of the fixed wires, and, equatorialh/, is 17-88. Two small gra- 

 duated circles, with their spirit levels, are fixed near to the eye 

 .piece for the purpose of finding a star's place in the meridiani 

 .Each circle is furnished with two verniers ; one for polar, the 

 other for zenith distances. 



