562 Reviews. | July, 
cyanogen. And here he appears to us to follow exactly the right 
course. But we do not understand why he has preferred to treat only 
of the metalloids in a work “intended as a handbook in Chemistry for 
students in Medicine and Engineering.” Any group of elements, no 
doubt, may furnish ample material for a volume addressed to scientific 
readers ; but what a beginner in chemistry needs is a sketch, however 
slight, of the whole subject; and it seems better that this should be 
presented to him in a continuous form than in a manual of the metal- 
loids, and, if such a work is to follow, a manual of the metals. 
A difficulty attendant upon the first steps taken in any science, is 
that of remembering or feeling an interest in the facts before acquir- 
ing some notion of the general principles under which they have been 
arranged, and on the other hand, of understanding the general prin- 
ciples without a knowledge of the facts. In chemistry, at any rate, 
there need be no hesitation as to the alternative a beginner ought to 
adopt. Dr. Apjohn has followed the usual practice in prefacing his 
detailed account of particular substances with an introduction, in which 
he deals with the laws of chemical combination, atomic weights, the 
classification of the elements, &c. We venture to think this practice 
inexpedient. Every teacher of chemistry must have had occasion to 
observe the bewilderment of a beginner, who attempts to read a 
manual in which this order has been followed. A curious compro- 
mise is adopted in the useful volume on chemistry, written by the 
late Professor Wilson for Chambers’s Educational Course. The first 
fifteen pages are occupied by an excellent account of the method of 
chemistry, and its relation to other sciences. Then follow fifty pages 
of theoretical explanations, also good, but to a beginner probably un- 
intelligible. In the preface, the reader is advised to skip these fifty 
pages, and pass on to the account of oxygen and hydrogen. The plan 
of first communicating some of the facts of chemistry, and then at- 
tempting their explanation, was adopted by Fownes, and is followed 
also by Dr. Bernays, in his ‘ First Lines in Chemistry.’ We cannot 
express too strongly our conviction, that in teaching natural science, 
the historical method should be followed as far as possible. The 
order of discovery, and of the development of scientific ideas, is 
obviously not fortuitous, but depends upon a natural connection be- 
tween one substance, or one mode of thought, and another ; and it is in 
this order that each learner will best advance from facts and ideas 
which he has already gained to others which to him are new. 
One difficult problem which the authors of scientific compendiums 
have to solve, is that of taking a comprehensive view of a large 
subject, and using the detail necessary for clearness, within the 
limits of a manual. They ought therefore to be jealous of admitting 
to their pages any matter, however useful, which will not directly 
serve the purpose of conveying to beginners a knowledge of the 
science. Too often the science lies buried beneath a mass of useful 
information. The process of purging itself of its applications is, 
we suppose, one that every science must go through at a certain stage 
of its development. Each kind of knowledge, before it has become 
extensive, and before it has imposing generalizations to show, is valued 
