SCIENTIFIC SUMMARY. 
323 
process, tlius : — A uniformly distributed load was applied on the girder, and 
ihe tension of every tie ascertained. Then a travelling weight was intro- 
duced, in addition, and hung at any one point, and the tension of every 
string was again taken, the difference of the tensions in the two cases being 
the thrust or tension due to the given travelling load. This beautiful 
acoustical method will no doubt be frequently employed, and for practical 
purposes leaves little to be desired. It does not, however, entirely get over 
the difficulty of ascertaining the effect of the rigidity of the arched boom of 
bowstring bridges. In the experiments Mr. Airy has made he has found 
the tension or thrust of every string to be proportional to the weight 
causing it, and the effect of several weights to be equal to the sum of the 
effects of the weights separately, and this is a confirmation of the accuracy 
of the method. 
• Liquid Fuel for Steam Boilers . — Capt. Selwyn, R.N., read a paper on this 
subject, before the Institute of Naval Architects, advocating the use of 
creosote, or ‘^dead earth oil.” This hydrocarbon does not inflame below 240°, 
and being heavier than sea- water, was, in his opinion, free from the dan- 
gerous properties which militated against the use of petroleum as a fuel for 
steam ships. The present price of creosote is 13s ^d. per ton. Its present 
production in the British Islands, as a waste product, probably reaches 60 
million gallons annually. In heating power Capt. Selwyn estimates 1 ton 
of creosote to be equal to 3 tons of coal, and he stated that an ordinary 
Cornish boiler had been at work, night and day, since Christmas, doing 
more duty with 230 gallons of liquid fuel per day, than it had previously 
done with 3 tons of coal. The evaporation of water amounted to 28 lbs. 
per pound of fuel. In another instance a still higher efficiency was 
reached. Mr. C. J. Richardson has formed a theory that the water, or 
steam, introduced with the liquid fuel, and which seems necessary to its 
successful use, is decomposed, and the heat of combustion of the hydrogen 
added to that of the liquid hydrocarbons. He has constructed a grate, in 
which he says the decomposition of the water, and the burning of its gases, 
can be seen. It is difficult to conceive that any additional heating effect 
can be gained in this way, but it is the theory of one who has worked 
earnestly and practically at the question, and whose experience has led him 
to believe that within twenty years, a locomotive or marine engine using 
coal or coke as fuel, will be looked upon as a curiosity, a relic of the olden 
time, as well as a rare piece of stupidity.” 
Gun-hoat ‘‘ Staunch.'^' — Messrs. Stephenson have constructed a small gun- 
boat, to prove that heavy guns may be carried by small craft for harbour 
defence, without incurring the disadvantages of unseaworthiness which so 
much marred the usefulness of the older gunboats. The Staunch ” is only 
150 tons displacement, with a mean draught of 6 ft. She carries a 12| ton 
Armstrong gun, which can be raised from or lowered into the hold b}”- a 
donkey engine actuating four screws simultaneously. A screen of iron plates 
sufficiently strong to protect the men working the gun from rifle shot, is 
constructed across the bows, but the vessel is otherwise imarmoured. The 
vessel has twin screws, and the gun is trained by turning the vessel. 
Governor adjustahle to various speeds. — In the Fngineer for April 24, will 
be found a paper by Professor Rankine on a governor for steam engines, 
