MARINE ENGINES. 469

3-9 x 2'6 i = io - i7", say 10", and allowing for two end abutment coils,say 11 34 ." = the length of spring before compression.

In cases where it is desirable or perhaps necessary to employsprings acting at the ends of levers, the same formulas can be em-ployed for determining the proportion of springs, bearing in mindthat the lift of the end of the lever where the spring is attached, isto be taken instead of the simple lift of valve.

The above illustrative calculations have all reference to springsmade of round steel, and used in compression. In many cases twoor more springs, one within the other, may be used with advantage.

After consideration of the whole of the experimental informationobtained, and the necessities required in practice, the committeehave come to the following conclusions:—

ist. The present practice in this country of constructing safetyvalves of uniform size for all pressures is incorrect.

2d. The valves should be flat-faced, and the breadth of face neednot exceed one-twelfth of an inch.

3d. The present System of loading valves on marine boilers bydirect weight is faulty, and ill adapted for sea-going vessels, a con-siderable quantity of steam being lost during heavy weather, inconsequence of the reduced effect of direct load—the result of theangle or list of the vessel, and also of the inertia of the weightitself, the latter not being self-accommodating at once to the down-ward movements of the vessel, and, moreover, the impossibility ofkeeping the valves when so loaded in good working Order.

4th. That two safety valves be fitted to each marine boiler, oneof which should be an easing valve.

5th. The dimensions of each of these valves, if of the ordinaryconstruction, should be calculated by the following rule:—

A =

18 x GP~

or A =

0-6 x HSP

A = Area of valve in square inches.

G = Grate surface in square feet.

HS = Hearing surface in square feet.

P = Absolute pressure in lbs. per square inch.

6th. The committee suggest that only one of the valves may beof the ordinary kind, and proportioned as above, and that it shouldbe the easing valve. The other may be so constructed as to liftone quarter of its diameter without increase of pressure. Valvesof this kind are now in use, and one such valve, if calculated by