64 Mr Wightman on the Advantages of the 
pense, got my first crane built, I consulted with a gentleman 
of considerable mechanical knowledge and experience as an 
engineer, who, after examining it, strongly advised me to 
break it up, without even a trial; and, from my confidence 
in his opinion, it was put aside a whole month, before I ven- 
tured to put it up for trial. 
Its decided superiority, easy management, and its capacity 
for forming an almost infinite variety of concentric circles 
(so much required in extensive building operations), were, in 
a short time, so manifest, that I had applications from seve- 
ral most respectable builders, to be allowed the use of the 
patterns for sets of castings. From this period my improved 
crane began gradually to come into general use; and I may 
be permitted to state, that the most of the bridges and via- 
ducts on the Edinburgh and Glasgow Railway were built by 
its means. I have seen it most successfully applied to ship- 
building, the derrick being no less than 70 feet in length, 
and capable of placing a heavy timber plank on any part of 
a large ship, besides commanding an extensive range of the 
yard for picking up timber. 
Fig. 1. is intended to represent the improved moveable- 
derrick crane, in its full proportions, as generally used; but 
as the mast and derrick may be increased or diminished to 
suit circumstances, there can be no fixed rule for the length 
of either. I have never used any mast less than 25 feet, or 
any derrick more than 55 feet; and where they are used for 
any purposes which require them to be frequently removed, I 
would recommend that the length of the derrick should not 
exceed 40 feet (unless the nature of the work require it), and 
that the derrick should never be lowered to a greater angle 
from the mast than 65 degrees, as the strain upon the der- 
rick-chain and stays of the mast, even at that angle, becomes 
very great. 
The size of the chain for raising or lowering the derrick 
is usually of the best cable iron, three quarters and one six- 
teenth of an inch diameter ; and the purchase or lifting chain 
of the same iron, but eleven sixteenths of an inch in diameter. 
With these, if judiciously stayed, the crane will lift or depo- 
sit, anywhere within its range, a weight of 4 tons. One thing’ 
