140 Analyses of Books. [Feb, 



till about ten in the evening. In the winter, the intensity is 

 much stronger than in summer. The greatest intensity appears 

 to happen n\ the month of January ; the least happened this 

 year (1820) on the 13th of July. The daily variations are much 

 greater in summer than in winter. 



" Great irregularities occur at times, especially on those days, 

 when the moon passes the equator, or on the quarter days of the 

 moon. Similar great changes I have observed during the equi- 

 noxes. The influence of the northern lights, as already observed 

 by Mr. Humboldt, is very remarkable, and frequently it does not 

 regain its former strength till after the lapse of 24 hours." 



" I have hkewise found in the same manner that every per- 

 pendicular object, of whatever materials ; for instance, a tree, 

 the wall of a house, &c. has a magnetic north pole at the foot, 

 and a south pole at the top." — T. T. 



A?i Essay on Chemical Analysis, chiefly translated from the 

 Fourth Volume of the last Edition of the Traitt de Chimie 

 Elementaire of L, J, Thenard, ivith Additions, cOmjnehending 

 the lattst Discoveries and Improvements in this Branch of the 

 Science. With Plates, By John George Children, FRSL. 

 andE. FAS.&c. &c. 



Chemical analysis, owing to the great number of simple sub- 

 stances with which the science has been enriched, and the con- 

 sequent increase of compounds, is now rendered a subject of 

 considerable difficulty and complexity. These have, however, 

 in many instances, been fortunately diminished by the discovery 

 of the doctrine of definite proportions, which the chemist may 

 now avail himself of in proof of the justice of his views, and the 

 correctness of his analyses. It must, however, at the same time be 

 admitted, that this discovery, vast as its importance is, is liable 

 to be, and probably has been, misused by some who have deter- 

 mined what the composition of a body ought to be, rather by a 

 comparison of numbers than by the slow and tedious process of 

 analysis. It is, however, to be remarked that the doctrine of 

 definite proportions, although it may be called in to prove the 

 correctness of an analysis, ought never to supply the place of 

 one — I do not mean that it is not allowable to form conjectures 

 as to the composition of bodies by the aid of the atomic theory; 

 I only mean that these conjectures should not be stated as facts 

 to be absolutely relied on. 



Mr. Children has stated so clearly the motive which induced 

 him to undertake the present work, that I shall give his own 

 words on the occasion : " On reading the fourth volume of 

 M. Thenard's Traite de Chimie Elementaire, Theorique et 

 Pratique, which treats exclusively of chemical analysis, and in 

 a manner much more satisfactory and complete than any other 



