344 
iron has hitherto been used, mass and stiffness due there- 
to, are required, rather than great tenacity and ductility, 
and there is, therefore, likely to be a simultaneous 
demand for castings of both steel and iron. Concurrently 
with steel castings, steel forgimgs have gradually been 
coming more and more into general use for fine and delicate 
work, where cost is no consideration, and homogeneity 
and capacity to harden of the very greatest importanre. 
“Steel has practically no grain, and is as strong in one 
direction as another; thus it is eminently suitable for 
such work, and is natural’, superseding iron completely. 
The conclusion of the !’resident on the subject of the 
employment of iron and steel in the arts is one in which 
upon full consideration all must agree—viz. that the laws 
of gradual change, and of the survival of the fittest, apply 
equally in the arts as in nature, and that in the long run 
the fittest material will prevail according to the peculiar- 
ities and necessities of each particular case. 
The first paper read at the meeting was by Mr. J. Ruston, 
M.P., descriptive of Dunbar and Ruston’s steam navvy. 
This machine may be described generally as consisting 
of a strong rectangular wrought-iron frame mounted on 
wheels. On the back end is placed the engine; at the 
front end rises a wrought-iron tower carrying the top 
pivot of a crane jib, the lower pivot resting on girders 
fixed to the main frame. The jib is of twin construction, 
being composed of two sides united only at the post and 
at the outer end or point ; between them is a long slot, 
in which swings an arm of adjustable length, depending 
from a fulcrum fixed on the upper member of the jib ; and 
at the base of the post is a circular platform, on which a 
man stands to regulate by means of a hand-wheel the 
“reach,” or length of radius of the arm. The scoop or 
bucket is fixed at the lower end of the arm, and is raised 
or lowered by the main chain passing over the extremity 
of the jib. The whole of the movements are controlled 
by two men, called the “driver” and the “ wheelman.” 
The driver raises the scoop while making its cut, swings 
it round into position for discharging, and back again 
afterwards, and lowers it down. The wheelman regulates 
the depth of the cut, releases the scoop from the face of 
the bank, and opens the door or bottom for discharging 
its contents. 
Supposing the navvy to be in position, the mode of 
working is as follows :—The bucket having been lowered 
till its arm is vertical, the wheelman regulates the length 
of the arm by means of his hand-wheel, so that the 
cutting edge of the bucket shall get its proper grip of the 
soil. The driver throws the main chain-drum into gear, 
and the scoop is dragged forwards and upwards by the 
chain, describing a circular arc of about 80 degrees. By 
the time it reaches the top it is fully loaded, and the 
driver, throwing the drum out of gear, holds it with a foot- 
brake ; at the same instant the wheelman by easing his 
footbrake allows the bucket to fall back so as to clear 
itself from the face of the bank. The driver next swings 
the jib round till the bucket is over the waggon, when the 
wheelman releases the latch by means of a cord, and the 
door falling open, the contents instantly drop through. 
The driver then swings the jib back again, and at the 
same time lets go the footbrake of the chain drum, thus 
causing the bucket to descend through a sort of spiral 
course, until he brings it up sharply by the brake again. 
The wheelman at the same moment adjusts the fall by 
means of his brake, so as to lower the bucket to its first 
position with just the right reach of arm for the next cut. 
During the fall the door of the bucket closes and latches 
itself automatically by its own weight; and all is then 
ready for repeating the operation. 
Upwards of a hundred of these machines are now in 
use, the majority in Great Britain, and the remainder in 
various parts of the world. 
In the discussion of this paper the various speakers 
testified to the success with which the navvy did its work 
NATURE 
[August 13, 1885 
when excavating materials of various degrees of hardness 
and toughness. 
Mr. John Richardson’s paper on recent adaptations of 
the Robey semi-portable engine was an extension of a 
paper read in 1873. The engine is erected on a massive 
wrought-iron foundation plate, to whichall the working parts 
are fixed, together with one of the drum-shaft bearings, 
and the brackets for carrying the brake-straps and levers. 
The whole of the strains due to the working of the 
machinery are contained within the base plate, and are 
brought, as they should be, near to the position of greatest 
stability—namely, the ground line ; while the boiler is 
set free from all mechanical strain, and is left to its legiti- 
mate purpose of making steam. A specially light engine 
has been designed for use in countries where there is 
little facility for transport, wrought iron and steel have 
been substituted as far as possible for cast iron, with the 
result of a large saving in dead weight and consequent 
saving in cost of transport. 
A paper on private installations of electric lighting, by 
Mr. Ralph Neville, is interesting as descriptive of an 
application in which existing engine power was utilised 
and modifications made in the governing of the engine to 
suit the purpose of driving a dynamo machine, in which, 
as is well known, the action on the engine has to be 
prompt, the electric lamps acting as visible instantaneous 
galvanometers. The dynamo employed was a Siemens 
S9,the lamps being mostly 100 volt 20 candle-power of 
Edison and Swan make. The current generated is led 
from the dynamo to a set of switches, by which it can 
be distributed into five separate circuits, the first exciting 
the field magnets of the dynamo itself and the others 
furnishing current for lights in various parts. Certain 
points are taken as lighting centres, and the electromotive 
force between them is kept constant ; for this purpose 
small wires are connected with the mains at the required 
points, and the current to actuate the governor is taken 
off there, instead of direct from the terminals of the 
dynamo. The original governor attached to the engine 
was found to have so great an inertia that its position 
would remain the same for a very considerable variation 
of speed, so the author set up an electrical governor. 
The regulating part of this governor consists of a double 
solenoid magnet, placed vertically and wound with 
insulated copper wire, within which works a double core ; 
and to the cross-piece at the bottom of the cores is linked 
the long arm of a lever, the short arm of which presses 
upon the spindle of a double-beat Cornish valve that con- 
trols the admission of the steam to the steam-chest. For 
incandescent lighting in parallel, the wire on bobbins is 
placed in shunt circuit between the main leads; and the 
size of wire used is adjusted according to the electromotive 
force which itis desired to maintain between the mains, so 
that when the electromotive force is at the right point the 
cores are suspended within the solenoids by their attrac- 
tion. Inasmuch as the resistance of the solenoids is 
fixed, any increase in electromotive force causes an in- 
creased current to flow through them, whereby the cores 
are immediately attracted with an increased force, and 
are caused to move upwards, thereby acting through the 
lever to close the valve until the electromotive force has 
been brought down again to its normal amount. The 
required movement of the valve is exceedingly small ; 
and this method appears to be the best suited for electric 
lighting. An automatic expansion-gear, on which the 
governor might be caused to act, has the disadvantage 
that, when but few lights are burning, the steam is cut 
off at so early a period of the stroke that, unless the fly- 
wheel is exceedingly heavy, a fluctuation occurs in the 
the light during the revolution of the fly-wheel. In an 
engine where economy of coal has to be considered 
probably the best way would be to have an expansion- 
gear actuated by hand, which can be set approximately 
to the expansion required leaving the throttle-value to 
