156 Mr Buchanan on ihd Strength qf' Materials. 
tried deviation from established rules : and, on this account, the 
progress of improvement must necessarily be slow, but there can 
be no doubt, that in this, as in other similar cases, principles, just 
in themselves, must, as heretofore, prevail in the end over our 
natural timidity, and be accommodated to practice ; and nothing 
can tend to promote such an improvement as a just and accurate 
knowledge of the laws of equilibrium, and of strength. To this 
alone can we look for that more perfect state of human acquire- 
ments described and anticipated by Dr Young, where principle 
is authorised to guide the operations of the artificer, instead of 
“ watching with servility the progress of his labours.” 
Throughout the various other public works, and the vast esta- 
blishments for which this country is so distinguished, we find 
every where equal reason to admire the application of the prin- 
ciples of strength, as well as to look for still more striking im- 
provements. But there is one department which merits parti- 
cular attention, and presents indeed, in itself, a wide and inex- 
haustible field for the talents of the engineer, namely the con- 
struction of machinery, and of the various kinds of moving en- 
gines. Professor Robison, in his valuable paper in the Ency~ 
dopcedia Britannlca^ and which has done more, perhaps, than 
any other work to promote the study of this subject, observes, 
there is nothing in which “ ignorance of principle is so frequent- 
ly observed, as in the injudicious proportions of the parts of 
machines, and other mechanical structures, proportions, and 
forms of parts, in which the strength and position are nowise 
regulated by the strains to which they are exposed, and where 
repeated failures have been the only lessons.” Much has been 
done since the above remark was made, but much still remains 
for future attempts. The strains which occur in machinery, are 
often of a very complex nature, and require, therefore^ consider- 
able attention and skill, both to appreciate their amount, and to 
oppose them with true and proper elfect. Here, also, every un- 
due weight of material is to be avoided, not merely from motives 
of economy, but as it clogs the motions of the machine ; and 
there are cases where this consideration becomes doubly import- 
ant. In those locomotive engines, for example, which have 
been introduced on railways in the coal-districts round Newcas- 
tle, their great weight and cumbrous structure, forms in itself a 
