This engine was made by Harvy and Co., Hayle Foundry, Cornwall, in 1864, was at work for six months at Chiverton Mine, after which it was removed, was purchased by Mr. Hall, brought by sea to Newcastle, and erected at the Lead Mine at Settlingstones in the year 1868, where it has been working ever since.

The engine is of the usual type of Cornish engine which is quite familiar to all engineers, and does not require any drawing to illustrate it. (See Plate 88, Vol. XIX., Page 202.)

The cylinder is 60 inches diameter, and is surrounded with a steam jacket covered with six inches of soil, cased with 9 inches of brick. The usual stroke of the piston is 10 feet.

The beam is 17 feet 4 inches long inside the house, and 15 feet 8 inches outside, giving a stroke of nearly 9 feet to the pumps.

The engine is worked by two double-flue Lancashire boilers 80 feet long, 7 feet diameter each, with two fire tubes 3 feet diameter. The fire-bars are 5 feet long. The flues are constructed in the ordinary way, and the boilers are covered with clay to a thickness of 12 inches above their tops.

The pressure of steam on the boiler is usually about 35 lbs. to the inch, and the gauge attached to the condenser stands at about 28¼ inches.

The engine makes about three strokes per minute, which is sufficient for the amount of work to be done, and at this speed developes about 36 horse-power, which is considerably within the power it could be made to exert.

Attached to the short end of the beam is a small 7 inch lifting set at the bottom pumping to 12 fathoms.

Next two 13 3/8ths lifting-sets pumping to 17 fathoms, and supplying the plunger set.

Again, one 18 inch plunger-set pumping to 37 fathoms.

It will be remarked that in the lifting-sets the weight of the two 13 3/8th columns per foot is 116 lbs. heavier than the weight of the single 18 inch column of the plunger-set, and as this 11.6 lbs. has to be lifted 102 feet, there is a loss of 1183 foot pounds per stroke.

These lifting-sets must, however, be somewhat larger than the single plunger-sets they supply, in order to prevent any possibility of the latter pumping on air at any time.

Two indicators about 4 feet apart were put on the forcing-set, one at A above the suction clack, and one at B above the delivery clack, Fig. 2, Plate X., and when at rest the pressure due to the column was found to be at A and B — 95 and 93 lbs. respectively. Immediately after the plunger had finished its upward stroke, it fell 2 inches before it became at rest, and the pressure at A went up to a mean of 127 lbs., the extreme range of the pointer reaching 160 lbs. (Plate XI., Fig. 1), it then dropped to 95 lbs., remaining there till the end of the downstroke, when it dropped to a mean of somewhere about 65 lbs., possibly through some small leakage of the suction valve; during the up-stroke the pressure became nil.

The vibration of the pointer was probably caused by its vis viva, after receiving a sudden shock.

The gauge at B reached an average of about 119 lbs. (Plate XI., Fig. 2), the extreme range of the pointer going up to 145 lbs., when the plunger was at the top-stroke, and came down to 93 lbs. before it began to descend, it remained there during the descent of the plunger, and then suddenly dropped about 20 lbs. as the plunger came to rest, going up to 93 lbs. during the rest at the bottom and the upward stroke.

Two indicators were similarly placed (see A B, Fig. 3, Plate X.), about 13 feet apart in the lifting-set, and the static pressure due to the column was found to be 37 and 30 lbs. at A and B respectively.

Immediately after the bucket had finished its upward stroke, it fell 2 inches before it became at rest, and the pressure at A went up to a mean of 62 lbs. (Plate XII., Fig. 1), the extreme range of the pointer reaching 8? lbs., it then dropped to 37 lbs., remaining there till the end of the down-stroke, when it fell to 32 lbs., probably through some small leak in the suction valve; during the up-stroke the pressure became nil. The guage was remarkably steady after the bucket began to descend.

The guage at B reached an average of about 49 lbs. (Plate XII., Fig. 2), the extreme range of the pointer going up to about 68 lbs., when the bucket was at the top-stroke, and came down to 30 lbs. before it began to descend it remained there during the descent of the bucket and the rest that followed, and then suddenly rose to about 53 lbs. on an average, the extreme range of the pointer going up to about 75 lbs., when the bucket began to ascend.

The indicator diagram, taken from the cylinder Fig. 1, Plate X., shows that the steam never rises above 16 lbs. to the inch, although the pressure in the boiler is 35 lbs. The throttle valve, which is 8 inches diameter, and which to give its fullest area should open 2 inches, is in fact only opened 3/8ths of an inch. It would seem, therefore, that a greater economic effect would be produced by cutting off still earlier and keeping the throttle valve full open. But the insufficient size of the suction clacks of the lifting-sets prevents this being taken advantage of. The vacuum in the cylinder is also not so good (11½ lbs.) as might he expected from the indication of the gauge 14 lbs., owing to the packing of the piston having been somewhat worn at the time the experiments were made; otherwise the diagram is most excellent, and gives at three strokes per minute 35 horse-power. The feed water is usually at a temperature of 600.

The economical working of the apparatus is not, however, in the application of the steam but in its production. The principles of slow combustion are carried out so fully that in bright sunshine it is difficult to see if the fire is alight or not.

In an experiment during 32 hours, the engine counter giving 5,640 strokes, 26 cwts. of small semi-bituminous coal from Fourstones Colliery were burnt, which is equal to .516 of a pound of coal per stroke of engine.

There was no direct means of ascertaining the exact quantity of water evaporated during this time, but if the water is calculated from the pressure, volume and quantity of steam used per stroke, theoretically the amount, though not exact, will err on the safe side; that is, practically, more water will be used than the calculation will give.

At the end of the stroke the pressure of steam above zero is 9.5, which gives a volume of 2551. The cubic contents of the cylinder (196 feet) divided by this gives .0770 cubic feet of water, or 4.8 lbs., or adding 5 per cent. for passages, 5.052 lbs. of water evaporated by 516 lbs. of coal, or 9.78 lbs. of water at 60 degrees, evaporated by one pound of small coal, or 10 lbs. of water at 100 degrees, the Government standard, taking the latent heat of steam at the pressure of the atmosphere at 988 degrees. This result is most exceptionably good, and will compare most favourably with the best result obtained by the Governments at Devonport in 1863. (See Transactions, Vol. XIV., which gave 10.71 lbs. of water at 1000 to 1 lb. of Davidson’s best Hartley, burnt in an ordinary marine tubular boiler without cleading.

When using large splint from Mickley this result was reduced to 9 lbs. of water at 100 degrees per pound of coal.

The following table gives a comparison between this engine and the Cornish engine described by Mr. Simpson in Vol. XIX., pages 203 and 219:—

On reference to Vol. XVII., page 22, it will be found that Mr. Steavenson stated that Mr. Henwood, at Huel Towan, after measuring the actual quantity of water delivered by a pump, estimated the deficiency at 7 to 8 per cent. of the calculated contents of the pump, and that from experiments of his own his deficiency ranged from 4 to 10 per cent.

This offers an explanation to the various pressures observed in the gauges placed in the pumps at the various portions of the stroke given in the table.

From many causes it is absolutely impossible, during the time occupied by the stroke, to fill with water a space suddenly exhausted by the rapid sweep of a bucket or a plunger.

In the case of the ascent of the bucket, as described, the whole column rests on the rods till the return stroke; and, at the moment of reaching the top, a rising column is rushing up through the suction valves towards the bucket.

At this point the bucket and the colunrn resting on it drops suddenly two inches and meets the column of water rushing into the pump, which it strikes with great violence and produces the extraordinary pressure indicated, which in this case is 1.7 times the static pressure due to the column.

Precisely the same result is obtained when the plunger of the forcingset drops the two inches and meets the water rushing up through the suction valve, producing a pressure in this case 13 times that due to the static pressure of the column. It will be remarked here that the blow takes place at a time when the column above the delivery valve is and has been at rest for some time.

There is, how ever, a physical difference in the nature of the two blows, the one caused by the free fall of a heavy column of water so many inches striking a column rising at the rate of possibly 5 or 6 feet a second with little or no elastic medium between them; the other, the blow of a certain weight of plunger and spear more or less balanced and restricted in velocity.

The effect of this is seen in the pressure increasing 1.7 times with the bucket, and only 1.3 times with the plunger at the turn of the stroke.

The causes which prevent a pump from filling itself perfectly full at each lift are various. Amongst others,

1st. — The suction clack valves fall as soon as the stroke is completed, and during the fall a certain portion of water falls with them.

2nd. — The friction of the water entering the snore holes.

3rd. — The sufficiency of the packing of the bucket.

The loss from these causes may be all increased by bad proportions.

There is one remedy which is generally most effective in preventing the violent blow caused by the return stroke, viz., the admission of a small quantity of air into the pump at each stroke. This can be effected either by a separate valve admitting the air but preventing the water from flowing out during the return stroke, or, in the case of a plunger, by slacking the stuffing box.

All pumps connected with fast working engines, such as are used on board ship, are provided with such valves, the absence of which would produce serious damage.

In conclusion, the author has endeavoured to describe fully the whole of the circumstances under which the engine performs, and will be most happy to add any further particulars that may be suggested during the discussion, if they can be practically arrived at.