REVIEWS. 
299 
number of these empirical dicta, with just sufficient explanatory matter to 
secure cohesion. Professor Unwin, however, as might have been expected, 
takes a much more lofty view of his subject, and while giving a collection 
of rules needful in the workshop, spares no pains to expose the theoretical 
aspect of machine construction. Between the man who works by mere rule 
of thumb and the man who follows scientific principles, there is of course all 
the difference in the world. As long as the same type of machine is being 
constructed, the old rules serve their purpose well enough ; but let new 
materials or new forms of construction be introduced, and the mere u prac- 
tical man ” finds himself immediately at sea. It surely needs no mean 
amount of scientific knowledge to determine how the parts of a complex 
machine should be duly proportioned, so as to best resist the action of forces 
acting both from within and from without. Machine design has indeed 
been raised to the rank of a science, mainly by Redtenbacher ; and in the 
work before us Professor Unwin has given an excellent compendium of the 
science in its present state. 
Evidence of labour conscientiously spent in the preparation of this work 
is unquestionably stamped upon its pages. While the author clearly 
explains the art of machine design, he takes care also to explain the prin- 
ciples on which the art is based; and as a necessary consequence of this 
treatment his pages bristle with formulae. Yet they are not in any wise 
formidable, and will present no difficulty to a student of ordinary intelli- 
gence. Scientific men might, perhaps, wish to see the metrical system of 
units introduced, but the old system here employed recommends itself by 
being familiar in all workshops. The work forms one of Messrs. Longmans’ 
series of “ Text-Books of Science,” and falls well within the original aim of 
the series — that of providing especially for the^ needs of candidates for 
Whitworth Scholarships. 
THE AMATEUR MECHANIC/ 
W ORKING with a lathe is so popular an amusement that Mr. Hobson’s 
little book will, no doubt, be welcome to many an amateur. It gives 
us, in very plain language, a good deal of information about lathes and 
lathe- tools, drilling and planing machines, vices and other appendages to 
the bench ; and it even touches upon the subject of brass-founding. As we 
read how to do this or that bit of work, we feel that we are being taught 
by one who has really handled the tools, and takes enthusiastic interest in 
his subject. Anyone attending to Mr. Hobson’s teaching ought certainly to 
be able to construct for himself a model of a steam-engine ; and, what is 
more than can be said of all home-made engines, when constructed it would 
probably work. 
* “The Amateur Mechanic’s Practical Hand-book, describing the dif- 
ferent Tools required in the Workshop, the Uses of them, and how to Use 
them ; also Examples of different kinds of Work, with full Descriptions and 
Drawings.” By Arthur H. G. Hobson. London : Longmans. 1877. 
x 2 
