Author: Sir William Augustus Tilden

Publisher: Theclassics.Us

Published: 2013-09

Total Pages: 28

ISBN-13: 9781230860466

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 edition. Excerpt: ...another as the atomic weights of the radicles in successive terms of a homologous series, the analogy is very remarkable. A single example will suffice: Now the several short series of elements when placed in parallel columns, as in the table given above, stand towards another in much the same positionas heterologous series of carbon compounds; except, of course, that while the latter can be transformed into one another, the former cannot. The periodic law, then, is based upon and includes the results of the earlier attempts at classification of the elements. All classification is founded upon the recognition of resemblances and differences, upon finding similarity in the midst of diversity; but to be useful a system must be based upon a record of as many points of resemblance as possible. Classification, therefore, implies, first, the practical process of observation, and, secondly, the survey of many observations, with a view to finding resemblances, so constituting the logical process of induction. In looking for indications of relationships, some considerable experience is necessary in many cases in order to select rightly among the phenomena observed and to assign to each its share of importance, so as to escape from the delusions to which the observer is exposed who gives too much attention to differences of colour, of density, or of mechanical condition. It is probably difficult for a young student to recognise at first the close relation subsisting between such substances as chlorine, bromine, and iodine. That a green gas should have much connection with a black shining solid, or even with a red liquid, doubtless appears at first a difficult proposition; and the conception that these three substances form a family having common...