the orifice Rt, R' t'; that resistance is represented by the 12 lbs. pressure on the surface of the concentre head of the valve.

Conceive T to have made its escape, there is now no resistance in front of D and H, and therefore there can be no fulcrum, and D and H will fall freely from P' to P, and from P" to P, at the same time their respective peripheries roll along R t, &c., and so long as the gauges show a pressure of above 12 lbs. so long will T be offering more or less resistance to D and H, but on the gauges registering 12 lbs., it is evidence that T is escaping freely, and the fulcrum of molecular force is entirely taken up and represented by motion of D and H along the line FO, representing the centre line of the current of escaping steam, and the lift of the valve being such that the stricture orifice just carries away as much steam as the seating orifice can supply to the chamber C, and F P having become a neutral line of force, the stricture orifice having become a perfect molecular vortex, the valve exists in the state of the balance. The spring now asserts its right to be master of the ceremonies, and closes the valve in virtue of the duty assigned to it.

Through the kindness of Mr. Thomas Gray, Assistant Secretary to the Board of Trade, I am enabled to supply you for publication the official report of the behaviour of the valve in question, on board the ss. Hoopoe, engined by Jack and Rollo of Liverpool, and, borrowing the dictum of the "surveyor," it will be seen by the rapid rise of the pressure that the boilers were excellent generators of steam.

(M. 8428.)

"Board of Trade, Whitehall Gardens,
"6th September, 1875.

"Steamships.

"Sir, I am directed by the Board of Trade to enclose herein, for your information, a copy of a report made by one of their officers as to the test for accumulation of pressure of the Spring Safety-Valves fitted to the steamship Hoopoe.

"Sir,-In accordance with M. 8428, I have the honour to report that on the 11th inst. I tested, under steam, Adams' Spring-loaded Safety

Valves as fitted to the boilers of the steamship Hoopoe, of Cork, with the results hereafter submitted :—

"Before beginning this test I had the fires put in the best possible order for generating steam, as the Board will see by the rapidity with which the steam rose during the twenty minutes' trial.

"These valves are, without exception, the most sensitive in their action of anything of the sort I have ever witnessed, the highest accumulation of pressure over the load being but

lb.

"I have to inform the Board that these valves are not quite in accordance with our rules, there are two valves on each boiler 34" diameter, and each boiler has got about 403 feet of grate surface, so that they should be 34", this fact I have acquainted the builders of.

It will be seen from this report of Mr. Herriot's, that an engineer sitting at the further ends of the earth, and with the Nautical Magazine before him, can tell whether the boilers were good or bad, whether

the coal was good or bad, whether the stokers were doing their duty or not, and whether the valves were efficient or non-efficient. Everything that he requires to be informed of on the subject is there before him. But although two valves are fitted to each piece of boiler, having 40 square feet of grate, only one valve was in action; the second valve being loaded 1 lb. above the other was not called upon to perform. It will also be seen that these valves are 7 per cent. less than the Board of Trade regulation prescribes; this was the result of a mistake, not that I wish to countenance any departure from the Board of Trade size of valve, for I can discharge a greater quantity of steam through the orifice of a Board of Trade valve than any other with which I am acquainted.

But good as these results are, they were beaten on board the steamship Britannia, belonging to the Pacific Mail Company, on the 18th inst. This ship has four pieces of boilers having 108 square feet of grate surface in each piece, and being fitted with a pair of 53′′ diameter valves to each boiler. These valves blew off at 65 lbs., and closed at 64 lbs., only a quarter of a pound between the greatest and least pressures, and only one valve in action, and not one solitary ounce of accumulated pressure could be got during the test, which was severe enough to satisfy the most ardent apostle of hot fires, for had his sulphuric majesty paid a visit to the stokehole while the surveyor and the Company's superintendent were there, he could have done none other than said, "Well done, good and faithful servants." These gentlemen, in physique fine specimens of the human race, stripped and entered the stoke-hole with composure, but with a will and determination which knew nothing but "duty" for the time being. Addressing Mr. Morrison, the Company's superintendent, the surveyor says, "Are your valves set ?"-" Yes." "What do you blow off at ?""65." " Well, get to the other end of the stoke-hole and wire-in. Here, stoker; hand me that shovel." And no knight of the shovel ever handled it to better advantage, for they made it ply between the bunker and firedoors with the dexterity of mountebanks tossing balls in the air. "Reach me that 'slice,'" says he, to another professional of the stoke-hole. He applied it, and the whole ship trembled under the draught of the fires, which continued for about twenty minutes, and finding they could not get the gauge above the blowing-off pressure, they gave in, filled the boilers up with water again, and then commenced his official "test;" at the expiration of which, they declared they had never seen the like of it in their lives.

This is a special and a marked ship for record, because she was fitted with certain other Patent Spring Safety-Valves, and was tested by the same surveyor. The other valves were loaded to blow off at 55 lbs., and when subjected to the Board of Trade test, the pressure rose to 85 lbs., and

was still going up, when the doors had to be opened to allow it to fall; when it fell to 40 lbs., at which pressure the valves closed-45 lbs. being the difference between the greatest and least pressures, just 180 times greater than the author's valve. The Board of Trade, very wisely, ordered their removal.

ON THE INCLINATION OF THE ANGLES OF THE ORIFICE FOR A MAXIMUM DISCHARGE OF STEAM.

Fig. 5.-Let A B be any orifice, of which Fig. 6 is a plan, discharging

seven molecules of steam at once, each one forms an angle of 60° with its neighbour, which entirely prohibits them from passing an orifice in a straight line. Their path is that of a helix.

Let B be any molecule making its exit at the orifice A B. Then BMB is the path of that molecule towards the orifice from the inside of the valve, and C D, Fig. 4, is the area over which the molecules must be collected in order to feed the orifice A B; it contains 37 molecules; but if the relative area of C D to A B be either contracted or enlarged, the result will be a depreciation of the value of A B; but B D must also bear a relative proportion to A B and C D, and if that proportion be disturbed,

the result is a depreciation of the value of A B as an orifice for discharging steam, and these proportions resolutely fix a relation between diameter and lift of valve.

ON THE "BOARD OF TRADE RULE

OF A HALF SQUARE INCH OF AREA

OF VALVE TO ONE SQUARE FOOT OF GRATE AREA.

Let Fig. 11 be the author's valve (applied according to the Board of

3",

Trade rule) up from its seat and in the act of blowing; it is a 3" diameter valve. It is required to find the opening of orifice which will discharge the greatest quantity of steam. Let A B be the diameter of valve = and a b be half the area of valve = 21", then the area A" will be equal to the area a". Draw the lines a a' b b'; draw ed e' d', equal to 36° from the horizontal line; draw da' intersecting a a' in the point a', such that e d d a' is proportioned to A C, C D in Fig. 5. Draw also a' N such that e N is proportional to A B in Fig. 5. The steam will pass out at e N in an orderly manner, because the velocity and quantity of steam passing by arrow 1 is equal to that at arrow 2, and the upper half of the orifice is equally as well fed as the lower half, and a uniform flow of steam through