Son; Have, you seen any other thing to convince you the air passed in and out of the strata?-Father: Yes; a number of men under my charge were working one day near to the workings of an old colliery. They holed into the old workings. When they had got a hole through, air passed through the hole into the old workings like air rushing to an up-cast near at hand. This enabled me and others to travel a great distance on the tramroads belonging to the old workings. The men with me were at a loss to know why air entered through the hole into the old workings; but, as I knew it was only a return of the weight or pressure of the atmosphere, I told them not to be surprised if to-morrow blackdamp rushed out of the hole from the old workings.

"

Son: And was that the case?-Father: Yes. One day we were able to travel into the old tram-roads a great distance; another day we were not able to get to the hole from whence damp came out. It was like a weather-glass for the men.

How or Why a Change in the Weather Affects the Workings of a Mine with Gases.

Son: Why are mines affected by a change of the weather? -Father: Because the weight of the atmosphere which presses gas in the strata is diminished. When a change in the weather takes place the weight of the atmosphere is diminished from 15lbs. to near 14lbs. This diminishing weight of the atmosphere causes an extra discharge of gas, as an extra discharge of steam would blow out of a boiler if a little weight was taken off the valve. The moment the pressure of the atmosphere is reduced, gas expands from every place into which it is compressed.

W

寫

Son: Do not miners often say, on seeing a cloudy wet morning, they will not be able to work that day? and also say so when the wind blows in a certain direction?-Father; Yes; the miner knows the weather affects his working place, but he

has not the knowledge to know how the weather affects his place.

A

Son: Are all working places so affected as not to allow the men to work when a change of weather takes place ?Father: All are more or less affected, but all are not so much as to prevent men from working in them.

Son: Why are not all affected alike ?-Father: Because some mines have very little air for ventilating purposesonly just sufficient to take away the gases on those days when little accumulates. Therefore, when a change of the weather takes place, the air is not sufficient for the extra quantity of gas generated.

2

1

Son: I see much caution and care is required to prevent explosions. Is there any forerunner to give notice to the men of a change in the weather, so as to have a knowledge of the extra accumulation of gases?-Father: The barometer will show when a change takes place, but will not show before the extra accumulation of gas commences. The change in the two is seen at one and the same time. Therefore, there is nothing to give notice beforehand.

де

Son: I think, father, I have a good knowledge, now, how mines accumulate gases. I shall be glad to know how mines are ventilated, and also to know the best way of ventilation to prevent loss of life; as there is often great loss of life by explosions, and great loss of life caused by not ventilating properly?-Father: I will give you a knowledge of several

م

ways of ventilating mines before I have done, as well as a knowledge of the best way, and what I say I know no one can contradict.

The cause why Air is Propelled down, through, and around the Workings of a Mine.

Son: Are not mines ventilated by a large furnace at the bottom of the upcast shaft?-Father: Yes; but there is the steam-jet, the bellows, and the fan employed also for ventilating mines.

Son: Well, but they do not, I presume, draw or pull air like the furnace through the workings of a mine?-Father: Air is not drawn through the workings by the furnace.

Son Miners often say that the larger the furnace, the more it will pull air through holes and places nearest the up-cast.-Father: I know miners often say and think so; they know no better.

Son: If air is neither drawn nor pulled, how is it caused to pass through the workings ?-Father: Heat, you know, will make almost everything expand, and, as air is elastic, cold air expands very much by heat; therefore, the furnace produces ventilation by making air hot at the bottom of the upcast.

Son: Then, when air expands, does it become lighter in proportion to its bulk with the cold air?-Father: Yes. If one foot of cold air expands by heat into two feet, the two feet, you know, will only weigh the same weight as one foot.

Son: Then heat makes air so light, that it rushes like a balloon up the upcast and out of a mine?-Father: Yes. And, with the air rushing up one shaft, the great weight of air in the other is too great to remain in its place; therefore,

it falls down or rushes forward to occupy the place of the hot air.

Son: I see; a furnace is like a pump emptying a shaft of water-as the water is pumped out it receives a fresh supply, which rushes in from the other shaft to occupy the place of that pumped out.-Father: Yes. If two shafts and the workings were full to the surface, with water, the yard of water nearest to the bottom would be pressed upon by the whole weight of water above it, and the water in the workings between the shafts would be pressed upon by the water from each shaft with an equal force. And it would remain stagnant, or motionless, unless an outlet was made for it, because the pressure of water in one shaft would be equal to that in the other. So in like manner will air press towards the up-cast as the pressure diminishes between the two.

Son: Air is not pulled, then, as miners often say, like something pulled or drawn with a rope, but is pressed into the upcast by the great weight of cold air in the downcast? But how does a steam-jet, a bellows, and a fan ventilate mines, as air is not made hot by them?

Father: Well, as you have asked me questions, all of which I have answered to the best of my ability, I will now ask you a few questions.-Son: I fear I shall not be able to answer your questions.

Father: The questions I require you to answer will be very simple.-Son: If so, I will try to answer them.

Father: By way of illustration, then, I will suppose you to have a pair of scales, with a 15lb. weight in one scale, and a 15lb. weight in the other: will the weight of one overbalance or weigh down the other weight?-Son: No. The

scales would be at a standstill, because the weights would be equal in the two.

ان

Father: Well, but if you add 1lb. more to one of them, making 16lbs. in one and 15lbs. in the other?-Son: That being the case the 16lbs. weight would be sure to weigh down the other.

1

こ

Father: But suppose you take off 1lb., making 15lbs. in one and 14lbs. in the other?-Son: If so, the 15lbs. weight would weigh down the 14lbs. with the same speed as the 16lbs. weighed down the 15lbs.

Father: Very well. By this I wish you to understand that the atmosphere presses with a weight of 15lbs. into and upon the top of the up-cast as well as into and upon the top of the down-cast, and as two 15lbs. will not overbalance each other, but be at a standstill, so in like manner will air in mines be at a standstill with an atmospheric weight of 15lbs. pressing at the top of each shaft, unless the weight is diminished or increased at either the one or the other. That is to say, all that is required to cause air to pass down one shaft and up another, is either to add to or diminish the weight of the atmosphere at either the one or the other shaft.

Son: Will the steam-jet, bellows, and fan diminish or increase the atmospheric weight at the top of either shaft?Father: It will send in a greater pressure, or force out the air at the top of the up-cast to diminish the pressure. Therefore, in proportion to its force it diminishes or increases the pressure of the air by which ventilation is produced.

Son: How wonderful, father, is ventilation, and yet so clear that if a blind man cannot see it he is as dark as midnight. But may a steam-jet or fan, &c., be fixed to work at the top of either